Ringmains = Good

The Advantages of the 32A Ring Final Circuit ©IEE/Miet 2007.

 The 230 volt ring circuit has been with us now in excess of 60 years. It was developed after the Second World War to minimise the use of copper in the massive reconstruction that followed the conflict. It was one of those simple ideas that now seems obvious, yet at the time was innovative.This installation methodology was introduced in 1947 following many years of debate which began in June 1942 with the first meeting of “The Electrical Installations Committee” of the IEE. The committee was formed by the Minister of Works and Planning, Lord Reith, “with the object of securing a comprehensive and co -ordinated review of building techniques for the guidance of those who would be responsible for the direction and organisation of building after the war”. The committee held 22 meetings between 1942 and 1944 which resulted in the publication of “Post War Building Study No. 11 – Electrical Installations” in January 1944 and the Supplementary Report in July 1944. The study led to the development of the Ring Circuit as we know it and also the BS 1363 fused plug and socket system. The study was remarkable in terms of its foresight. It refers to topics such as Energy Efficiency and Environmental Protection, topics which are much more relevant now than they were in 1944. The advantages are clear. To feed a given number of socket outlets using a ring main requires less copper and fewer protective devices. The benefits, however, do not stop there. The concept of the BS 1363 fused plug allows the devices connected to the ring to be appropriately protected on an individual basis. The standard fuses available are 13A, 5A & 3A, which covers the requirements of domestic devices from washing machines to reading lamps and commercial devices from copiers to calculators. Prior to the development of the BS 1363 fused plug and socket system we were using differently sized 2A, 5A and 15A outlets, which led to different circuits for the different outlets and a multiplicity of plugs and sockets. Oddly enough, that remains the current situation in Europe, but many countries that have historic links with the UK have adopted the BS 1363 Fused Plug.2.0 Application of Ring Circuits

2.1 Domestic Premises:

In the years since 1945 the types of appliances in use in our houses have changed dramatically. From 1945 up to the early 60’s, 3KW heaters would be used to supplement open fires. Light current devices would be restricted to reading lamps and radios. From the early 60’s onwards we saw quite a dramatic change in domestic usage. The one having most impact was the gradual introduction of central heating, which removed the need for supplementary electric heating. Increasing prosperity led to the purchase of labour saving devices such as fridges, washing machines, toasters, record players and alarm clocks. Generally the effect was to reduce demand during the winter months and lead to a more level demand profile through the year. Present domestic demand is tending to reduce even more with the move to the use of energy saving devices. Washing machines, fridges, freezers,tumble dryers and electric irons all display their energy saving credentials.These devices tend to be grouped in the kitchen area whereas the rest of the house uses low current devices such as television sets, music centres,computers, printers, radio alarms, reading and standard lamps, and wireless telephones.All these devices are economically catered for and protected by the 32 amp ring main and BS 1363 fused plug. It is now the trend that the devices are supplied with a molded plug fitted with the appropriate fuse.The 32A ring main has stood the test of time and is well placed to serve the needs of our homes for the foreseeable future.

2.2 Commercial Premises:

The use of electrical equipment within commercial premises has also changed considerably over the last 60 years. Mechanical typewriters have been replaced, initially by electric typewriters then by computers. Carbon copies have been replaced by the photocopier. All employees are now provided with computers. Desks have become work stations requiring multi- point outlets to power computers, monitors and local printers.Designers are continuing to use ring circuits to support small power requirements in offices where the power requirements are moderate and a benefit can be gained from the use of rings. 20A or 32A radial circuits are seldom used in the UK.Where demand is high and frequent ‘churn’ of personnel, desks and workstations occurs, outlets are increasingly powered from under floor bus- bar trunking systems with multiple and regular tap off facilities.Ring mains continue to be used to provide circuits for cleaning equipment.The diversity on such circuits is high and the use of a ring guards against voltage drop problems on distant outlets.

2.3 Retail Premises:

In the retail area we have seen the demise, to a large extent, of individually owned corner shops and the emergence of supermarkets. American style shopping malls are present in most of our towns and cities. Out of town retail parks provide outlets for DIY stores, white goods retailers, Hi-Fi special lists and computer retailers.A mixture of ring and radial circuits are used dependent on the consequences arising from circuit failure. Freezers in a supermarket are fed individually from the distribution board to minimise losses on circuit failure. Designers will generally use ring mains for non – critical circuits.

2.4 Industrial Premises:

Office areas will be treated as Commercial premises. Outside office areas the provision of 230 volt outlets will generally be restricted to those needed for hand tools and cleaning systems. The outlets will be widely spaced and a highl evel of diversity in operation can be anticipated. Ring circuits are again beneficial over radial circuits, both to reduce voltage drop and to reduce the number of protective devices needed at the distribution boards.

2.5 Additional uses for Ring Circuits:

The 230 Volt 32Amp ring circuit has proved beneficial in reducing the cost and increasing the flexibility of small power provisions within buildings in the UK.The use of rings need not be restricted to this particular function and designers are using them for other purposes.Examples of additional uses for ring circuits are:

-2.5.1 External Lighting:External lighting to a building may cover an extremely large area, including walk ways and landscaped area. Providing radial circuits to strings ofluminaires may be relatively expensive because of the need to reduce voltage drop to acceptable levels. Connecting the luminaires in a ring gives a useful option for reducing voltage drop to required levels at relatively low cost.

2.5.2 Hi – Bay Lighting:Hi – bay lighting in industrial buildings, warehouses, and even some supermarkets or retail park outlets may cause problems in terms of voltage drop. The use of ring circuits can alleviate the problem in the same manner as that described for external lighting.Designers have found ring circuits beneficial for other applications where theycan be used to reduce cable sizes and switchgear provision.

3.0 Operational Experience:

The UK has been using the 230 volt 32A ring system to meet the small power requirements of a wide range of buildings for over 60 years. It is sensible to look at the experience we have gained to see if the system can be improved to advantage.Experience indicates few problems. The test procedures ensure that all circuit conductors are properly connected and that no bridges exist across the ring.
The Wiring Regulations “Onsite Guide” describes the how the tests should be carried out and also defines the parameters governing the use of the circuit,such as area to be served and number of sockets allowed. An unlimitednumber of sockets are allowed in any 100 sq m area.4.0 Potential Faults. There are potential installation faults, which are caught by the test procedures.
4.1 Disconnected cable, leading to lack of circuit continuity.
4.1.1 Live or neutral cable.If either the live or neutral cable is discontinuous at any one point, the ring will still function at all outlets, but the circuit is now two parallel feeders connected to a 32A protective device.If the break is at the centre of the ring and the load is distributed evenly around the ring there would be little problem. If, however, the break is towards one end of the ring, one cable will be taking the majority of the load current and risks over load. Testing in accordance with recommended procedures will find any break in the ring and allow remedial action to be taken.Experience of the last 60 years has not revealed this to be a common problem, which is down to the skills of our electricians and the vigour of the testing regime.On a radial circuit such a problem would be apparent to users since outlets down stream of the fault would not function.
4.1.2 Earth Continuity Cable If the earth continuity cable is disconnected at a point around the ring, there will still be earth continuity at each socket. To this extent the ring is safer than the radial circuit. Loss of an earth continuity conductor on a radial circuit may not be noticed until a shock is received.
4.2 Bridging. If a bridge is introduced across a ring circuit, the cost efficiency of the installation is diminished and current is shared between two parallel paths.This is not dangerous in normal use but could cause problems to a nun suspecting electrician working on the circuit in the future. Again testing will identify any such error.The testing regime has been proven to work effectively and problems seldom arise on either ring or radial circuits.5.0 IEE Wiring Regulations Guidance on Final Circuits. The IEE guidance on Standard Circuit Arrangements for Final Circuits used to be in the body of the Wiring Regulations, but is now located in Appendix 8 of the “On Site Guide”. The Standard Circuits covered are:• Final circuits using socket outlets complying with BS 1363-2 and fused connection units complying with BS 1363-4• Cooker final circuits• Final radial circuits using socket outlets complying with BS 4343 (BSEN 60309-2)Final circuits using socket outlets complying with BS 1363-2 and fused connection units complying with BS 1363-4.The options on offer are tabulated in Table 8AFinal circuits using BS 1363 socket-outlets and connection units Minimum conductor cross-sectional areaType of circuit Overcurrent protective device Rating A Copper Conductor thermoplastic or thermosetting insulated cables mm² Copper Conductor mineral insulated cables mm² Maximum floor area served m21 2 3 4 5 6A1 Ring 30 or 32 2.5 1.5 100A2 Radial 30 or 32 4 2.5 75A3 Radial 20 2.5 1.5 50It is clear from the table that the specification of Ring final circuits will result in the use of less copper and less circuit protective devices than will the use of either type of Radial circuit.It is important to note that the guide also states “Circuit arrangements other than those detailed in this appendix are not precluded when specified by asuitably qualified electrical engineer, in accordance with the general requirements of Regulation 314-01-03.”This allows the designer to develop final circuits covering different floor areas and using different ratings of protective devices if he determines that the current drawn by devices connected to the circuit and the diversity in use between the devices would allow different circuit arrangements to be used with benefit.It is also important to note that the “On Site Guide” does not express any preference between ring or radial circuits. Both circuits are available to designers for use on their systems as they see fit.Conclusions. It is my firm belief that the present guidance provided by the IEE Wiring Regulations is sound in concept and in practice. Advice is given on the use of Radial and Ring Final Circuits and no preference is assigned to any circuit.Designers are free to choose any of the three standard circuits or develope the circuits to suit any particular need.For my part I will continue to favour the Ring Final Circuit for the following good reasons
1. It reduces the amount of copper used in an installation
2. It reduces the number of circuit protective devices
3. It helps to reduce voltage drop
4. It has proved its value over the last 60 years
5. It promotes sustainability in design
6. It is good for the Environment I know many of my colleagues agree with the above principles and will continue to include Ring Final Circuits in their designs.I invite you to join with me and use the Ring Final Circuit to the benefit of the consumer, the environment and the economy.

Ringmains = Bad

Ring Circuits – The Disadvantages by Roger Lovegrove Introduction

Have we got it right or is this yet another UK outdated insular custom? In this paper I intend to show you the disadvantages of using ring circuits. Opinions I have formed as a result of problems experienced during many years of inspecting and testing electrical installations and training people to do it. David has pointed out that the original thinking behind the development of the 13 amp plug and socket system was for domestic premises – economy homes. Having read David’s paper, it seems to me that the introduction of ring circuits was almost an afterthought and that the original intention was for a socket to be used on a radial circuit. In my view it should have stopped at domestic premises. Other premises were only mentioned once in the history paper. However, over the years people have been brainwashed into believing that 13A sockets mean ring circuits.I have just recently even found a ring circuit supplying a single socket for a heating boiler. Hardly dangerous but demonstrates a complete lack of understanding by the installer, who incidentally was Part P registered.
Usage. Ring circuits are used almost everywhere in this country, and some others:Schools - laboratories and workshops Offices both large and small Hospitals – wards and surgical/treatment areas Retail premises, although some will not have ring circuits because of additional dangers and costs. Public buildingsAs well as Domestic At this point I would like to make it clear that I am not against ring circuits, there is aplace for them in modern installations provided they are properly designed inaccordance with BS 7671, carefully installed and tested as detailed in IEE Guidancenotes 3 or the On-Site Guide. If all three were properly applied some of the disadvantages would disappear.

Main Issues.
Safety is the main issue and safety being important becomes one of the main disadvantages. Ring circuits are misused and abused. They are installed without proper consideration as to their purpose and loading, additional points are frequently added as spurs without considering the existing layout of the circuit.They are used for heating circuits and IT circuits again, without considering the load or the need for secure protective conductor connections or reinforced cpcs.The ring circuits cost more to install than two radial circuits. Regulations – 433-02-04BS 7671. There are only four regulations that state requirements for ring circuits.The critical regulation is 433-02-04 which is probably largely ignored because it isoften impractical to apply. This regulation requires the load to be distributed aroundthe circuit so that the current in any part of the ring does not exceed the installedrating of the cable. This means that in a circuit intended to supply a washingmachine, tumble dryer and a dishwasher the points need to be wired so that the loadcurrent in both legs of the ring is shared as equally as possible. More often than not if you look around a kitchen you will find the washingmachine, dryer and dishwasher grouped around the sink, for obvious reasons. And if the sink does not happen to be more or less in the centre of the ring, one leg will carry more current than the other.

Disadvantage:
Not easy to achieve. Regulation 543-02-09Regulation 543-02-09. This regulation requires the protective conductor of a ring circuit to be wired in the form of a ring, unless it is formed by metal covering or ametal enclosure. Most people ignore the metal covering part and run separate cpcs for each circuit. Hence metal trunkings become half filled with green and yellow cables that are unlikely to ever see an amp in their whole existence. Disadvantage: Waste of cable and labour.Safety Many rings are wired incorrectly particularly by DIY persons. Sometimes however electricians can get it wrong. I have had electricians say to me “I can’t believe I did that” Even competent people make mistakes at times. Another disadvantage.A lack of understanding of the system is another problem. Unless a ring circuit is wired correctly with spurs restricted to 1 double point per spur,there is an increased fire risk due to overheating of cables and connections.If there are breaks in the conductors or loose connections in terminals there are both fire and shock risks.Testing The safety of a ring circuit relies on proper testing. It is a vital part of the installation process. If the correct testing method is not fully applied defects with the circuit are unlikely to be identified and corrected. This applies to both initial testing as well as periodic inspection and testing.Testing is however a time consuming and expensive operation, hence it is very often not done fully as prescribed in GN 3.History IEE Wiring Regulations - 13th Edition 1955 Regulation 505A test shall be made to verify the continuity of all conductors of every ring circuit installed in accordance with Regulation 114 (b)IEE Wiring Regulations - 14th Edition 1966 Regulation D 10A test shall be made to verify the continuity of all conductors (including the earth-continuity conductor) of every ring circuit.No test methods givenIEE Wiring Regulations – 15th Edition 1981 Regulation 613-2A test shall be made to verify the continuity of all conductors (including the protectiveconductor) of every ring final circuit. See Appendix 15.Appendix 15 showed a very detailed test method.WHY?There must have been a reason to introduce a specific test method in Appendix 15.Could it have been that the industry and consumers were having safety problems? It is clear to me that in the 25 – 30 years following the introduction of the ring circuit there must have been safety problems that were referred to the IEE for resolution andbecame the driver for the test we have today. I am sure that it could not have been simply 'a good idea at the time’ IEE Wiring Regulations – 16th Edition 1991 Regulation 713-03A test shall be made to verify the continuity of all conductors (including the protectiveconductor) of every ring final circuit.The test method was transferred from Appendix 15 to Guidance Notes 3.Test Methods The method introduced into the 15th edition called for a resistance measurement to be made at every outlet point first between phase and neutral and then between phase and cpc, with the conductors joined together at the distribution board. The text said that the resistance at the centre point of the ring would be equal to the sum of the phaseloop resistance and the neutral or cpc loop resistance, divided by four.This sent everybody running around like headless chickens looking for the mid-points of ring circuits. Consultants were marking the mid-points on drawings or instructing contractors to label the socket at the mid-point, or marking the mid-point on the ‘as installed’ drawings.What a lot of nonsense.If the text had said that the highest value of resistance measured between phase and neutral, or cpc, with the conductors joined at the distribution board, should be a quarter of the sum of the conductor resistances added together, and all other points would be of lesser value, it would have saved the industry a great deal of unnecessary work time and cost. Happily this method was changed for the 16th edition.The 16th Edition Method.The recommended and only proven method of testing involves breaking the ring,separating the conductors at either the distribution board or at a point, doing the tests and re-assembling the circuit after completing the tests. How can one be sure that the ring is complete after reassembly? Still a funny way of doing things! Is this a disadvantage? In many instances, probably most, ring circuits are not properly tested.Most people testing will test the ring ‘end to end’, many cannot be bothered to do the‘interconnected conductors’ test. Electricians freely admit this because testing eachpoint twice takes too long.None of the test results schedules that I have seen provide for the ‘interconnectedconductors’ test value to be recorded. This is an important record that demonstrates:a) the test has been done and b) the circuit is correctly wired.If suitable provision were made in the schedules of tests results there is a chance that the testing would be done properly.

Typical Faults Found

The most dangerous fault:
Cross connections between two ring circuits or a ring and a radial so that the over-current and fault current protection is compromised becoming as much as 60 or 64 amps, disconnection times are completely blown and circuit isolation relies on 2 devices rather than a single device. Interconnections occur usually in distribution boards but can easily occur when ring circuits cables are installed in trunkings.
In one hospital, sockets mounted in dado trunking were intended to be connected alternatively to essential and non-essential supplies distribution boards. The circuit cables were inter-connected between the two boards. Would have had an interesting result if the circuits had been connected to different phases.
Other Faults
Incomplete ring on one or all circuit conductors – broken loops Part of a ring missing, a link cable having been left out, resulting in two 2.5mm2
cables being protected by a single 32 A protective device
Loose Connections due to conductors crammed into back boxes that are too small, especially for spurs, one cable not secured and overcrowded distribution boards.
Too many spurs on a ring, and spurs on spurs - risk of over-heating
Spur cables too long. A ‘ring’ wired as a figure of eight, risk of overloading 1 leg of the ring
Break or loose connections in the live conductors, 3 conductors in one terminal, one loose. Overheating likely to cause a hot spot at a termination that may eventually burn out or cause a fire.
Break or bad connection in the cpc due to loose screws or over zealous tightening, thus increasing Zs of the circuit so that the limiting value is
exceeded and the 0.4 second disconnection time is not achieved.
Incorrect polarity. All these could cause danger and are therefore serious disadvantages. They would be eliminated by applying the correct testing methods.
Testing ring circuits can take 5 or 6 times longer than testing radial circuits, and if any of the above defects are present fault finding can take a considerable time and become very expensive. Fault finding on radial circuits is relatively simple and quick.
Big disadvantage to the installer. Who pays in the long run?
Disadvantages galore, can’t happen with radials Installation
Consider the disadvantages with circuit wiring:
A 32A ring circuit serving 100m2 uses more cable and therefore takes longer to install
than 1 x 32 A radial circuits serving 100m2
A 32A ring circuit serving 100m2 uses more cable and therefore takes longer to install
than 2 x 20A radial circuits each serving 50m2 the latter having a higher loading
capacity of 40A.
Ring circuits wired with 3 single core 2.5 mm2 cables drawn into a straight run of
conduit or trunking take much longer to install than radial circuits wired with 3 single
core 4.0 mm2 cables.
Each of these situations use less of the worlds resources of copper.
To my mind, in offices, workshops, classrooms and laboratories the only justification
for installing a ring circuit is where a single circuit is run completely around the room.
If it is necessary to install all 6 conductors in a single run of conduit or trunking then 2
radial circuits are much more practical and cost effective.
I have discussed this with many engineers who all agree with this philosophy. I know
that some engineers will not consider using ring circuits in commercial installations.
Additional points. Domestic and commercial consumers have a multitude of low-current
appliances. New installations need many sockets and flexibility is needed to
allow furniture to be moved around and for future alterations and additions.
Extending or breaking into a ring circuit is not a straight forward exercise.
Many domestic ring circuits have been modified incorrectly by DIY persons
and are no longer a ring and are probably unsafe.
More often than not, particularly in domestic premises, additional points are installed
as spurs from the ring or spurs from spurs, with total disregard for the existing load
and usage. This can, depending on the load, change the balance of the circuit.
I am sure that nobody ever tests the ring continuity and layout prior to installing an
additional point. I am equally sure that very few people install an additional point by
diverting the ring cables to include it in the ring. Furthermore I am certain that very
few people, especially DIY, ever apply the ring test after installing the additional
point.
Unless thorough testing is carried out on a new or particularly a modified ring
circuit, wiring faults may go undetected and invalidate the basic safety
principles of the system.
Another potential danger and disadvantage.
Training
It has been said many times that if electricians are trained properly the problems
would not exist. I do not disagree with that. An apprentice who is brought up with the
system should understand the correct installation methods, however testing is a
different issue. I have found that some electricians, who may be exceedingly good
tradesmen, have great difficulty in grasping the test method and the benefits of doing
the test, and are likely to give up. Others swallow it whole and become very
competent testers.
We have big labour problems in this country. There is a dearth of competent home
grown time served electricians.
Much of our labour comes from agencies and you get what you are sent. In London
you hardly ever hear English spoken on construction sites. Electricians trained in EU
countries other than Ireland will not have heard of ring circuits. They may be very
good competent tradesmen in their own countries but never-the-less are not competent
to install socket circuits in this country.
Europeans do not understand ring circuits. This also applies to Australians, New
Zealanders and South Africans many of whom come to this country to make a
fortune.
To my knowledge, agencies do not apply a trade test before taking such people on
their books. They may require proof of qualification, unlikely, but that is all. It is
hardly surprising that there are problems. In these circumstances independent testing
is essential, but is it done? It becomes expensive for the contractor and ultimately the
client.
A big disadvantage for some.
Other Options: Radial and Tree Circuits
There are good reasons for considering the use of other types of circuits
IEE Guidance Notes show radial circuits in the conventional circuit arrangements.
• 32 A ring – 7 kW – 100 m2
• 32 A radial – 7 kW – 100 m2
• 20 A radial – 4.5 kW – 50 m2
In my view
• 2 x 20A radials better than 1 x 32A ring
A 20 A circuit to serve 50 m2 floor area and a 32 amp circuit, 100 m2. These are
based on the maximum anticipated load in these areas not exceeding 5 kW or 7 kW
respectively.
The limiting factor in such areas is the cable length - voltage drop and the earth loop
impedance of the circuit. Voltage drop is unlikely to be a problem neither will earth
loop impedance because in the near future all such circuits will require RCD
protection. The limiting factor need only be the maximum anticipated load that would
be used in the area. It is now recommended that kitchens are treated as a separate entity and have at
least one ring circuit. 2 x 20 A radial circuits in a kitchen will use less cable than a ring circuit and
provide greater capacity as long as care is taken to ensure that fixed loads such
as washing machines, driers etc are not all on one circuit.
Tree Circuits
A tree circuit is simply a radial circuit with branches. A 20 A tree circuit wired with
2.5 mm2 cables would be far more versatile than a straight radial circuit and probably
far more practical. Points could be placed economically wherever they may be used,
the limitation would still be the maximum load likely to be used in the area, not the
number of sockets.
Controls Ring circuits do not readily facilitate separate control of groups of socket
outlets. Radial and Tree circuits do.
This added bonus gives an opportunity to control sections of the circuit separately
with switches and timers.
In Commercial buildings by Building management systems
In domestic buildings – Smart Homes – Home Bus Systems, automatic and telephone
control.
Applications
Typically a standard 3 bedroom domestic property could be adequately served by
2 x 20 A 2.5 mm2 radial or tree circuits, and
1 x 32 A 4.0 mm2 radial or tree circuit in the kitchen.

Now that the UK electrical industry has finally seen the latest changes to the 17th Edition of the IEE Wiring Regulations (BS 7671), Alan Roadway, Product Manager for ABB's Low Voltage Distribution Products business, explores the new mandatory use of Residual Current Devices (RCDs) and the consequent effects:

Ammendment 1 comes into force January 2012

Whilst residual current devices (RCD) have been in use for many years, the new 17th Edition requires electricians to consider the use of RCDs in many more applications than the current standard requires in order to improve building protection.

The basic function of an RCD is to trip and disconnect the supply of electricity in the event of an earth fault in order to prevent electric shock and fire risk. It does this by detecting the imbalance of currents between the live and neutral lines caused by a fault to earth. Drawing attention to the importance of using RCDs in the right context and with the right equipment, the IEE Wiring Regulations provides guidance on how RCDs should be incorporated in new builds.

One example is the requirement for cables concealed in a wall/partition at a depth of less than 50mm in domestic installations. Such cables will need to be protected by an RCD rated at 30mA or below, even if they are in a safe zone. This has implications for lighting circuits, which - under the still current 16th Edition - have no requirement for RCD protection. Note that both 16th and 17th Editions are run in parallel until full implementation on July 1st 2008, after which all new installations, alterations and additions designed on or after 2nd July will need to comply with the new requirements.

The only exception to this will be if the cables are enclosed in an earthed metallic covering / conduit or equivalent protection capable of resisting nails, screws etc. This is also the case for cables installed in metal-framed walls - a very popular construction technique at the moment.

30mA RCD protection for ALL sockets:

Additionally, all socket outlets rated at 20A or below within a domestic building will require 30mA RCD protection*. This means that all ring main circuits from consumer units will either need to be fed from the RCD side of a traditional split load board or have individual residual current breakers with overload (RCBO) ways.

Because the RCD is sensitive to current imbalances, it is not practical to fit just one device to protect an entire house. If a fault develops within one circuit, all circuits would be switched off immediately. By using individual and grouped RCD protected ways in combination with one another, the required protection can be provided whilst maintaining continuity of supply to other non-affected zones within the installation

Much more detail required:

However, this does mean that, for architects, builders and electricians, much more detail must be put into the design and implementation of any new building supply. Now, utility rooms and storage areas will require specific design and consideration based on the devices installed. Bathrooms are under particular scrutiny. The new regulations will require RCD protection for all circuits supplying electrical equipment within Zones 0, 1 and 2 (Zone 3 is being removed). In addition, all cables buried in walls surrounding bathrooms must have 30mA RCD protection - regardless of the points they are supplying. This could have significant implications on the routing of cables to avoid crossing these zones within ceiling voids and adjoining walls.

Many of the changes to the 16th Edition are part of a harmonisation process to create commonality of installation standards throughout Europe and the world. Whilst the 17th Edition sees an increase in the use of RCDs, it is unlikely that the products themselves will change dramatically as they are have been designed and manufactured to the harmonised and 'normalised' European and worldwide standards in any case.

With more regulations to consider, the IEE Wiring Regulations encourage communications across the industries and enable a more harmonised approach towards building. Now, builders, electricians, designers, manufacturers and our clients will all need to be able to discuss the practices required to meet the new regulations and ensure greater health and safety for any building's inhabitants.

For more information about the RCD options available from ABB, please email \n This email address is being protected from spambots. You need JavaScript enabled to view it. "> This email address is being protected from spambots. You need JavaScript enabled to view it. or call 0800 269 371 to request further information.

*For all socket outlets for use by 'ordinary persons' i.e. a person who is not a skilled or instructed person.

THE USE OF THE ARMOUR OF STEEL WIRE ARMOURED CABLES AS A PROTECTIVE CONDUCTOR

Please read all pages!

The Problem Encountered

1. The use of the steel armouring as a CPC with the cable terminated at each end in brass glands.
2. The use of an internal core as a CPC in addition to the SWA with both ends terminated in brass glands.
3. The use of an external green/yellow single core PVC CPC run in parallel with the SWA cable with the cable terminated in brass glands.
4. The use of an internal core of the SWA cable as a CPC with no cable glands and the cable ends inserted in to enclosures.
5. The use of the steel wire armouring as a CPC with no brass glands and “Tenby” type bonding clamps on to the exposed steel armouring with a green/yellow single core PVC CPC on to the clamp.
6. The brass glands terminated with and without the earthing ring ( Banjo).

Information Requested

I have asked experienced electricians in the field and students at the college where I teach why external CPCs are used and why cable cores are used for a CPC. The answers varied wildly both with and without logical reasoning. I have particularly probed the respondents with the question of the use of 3 core cable on single phase circuits. The cable is manufactured in both old and new harmonised colours for 3 phase. The use of this cable requires the over sleeving of cable cores to single phase colours and green/yellow for the CPC. Often this over sleeving is not provided. I have tested the advocates of the use of 3 core cables on single phase as to why they think 2 core cable is correctly coloured for single phase use.

The STUDENTS responses to questions can be reduced to those listed below or a combination of these.

1. The steel wire armouring cannot be relied on as a CPC.
2. The use of the armouring is as a CPC is not allowed in the “regs” (BS7671).
3. An external CPC is needed as the SWA is not big enough.
4. An internal core is needed as a CPC as the SWA is not big enough.
5. The SWA does not need to be earthed as it is not an exposed conductive part.
6. It is not good workmanship to use the SWA as a CPC.
7. I have always done it that way.
8. Banjos are not needed as the brass gland is the same as terminating conduit or MICC cable.
9. You cannot use the SWA as a bonding conductor.
10. It is dangerous to terminate both ends of the SWA

Defining Protective Conductor

Protective Conductor is defined in BS7671 under Part 2 Definitions as:-

A conductor used for some measure of protection against electric shock and intended for connecting together any of the following parts:

1. Exposed conductive parts.
2. Extraneous-conductive parts.
3. The main earthing terminal.
4. Earth electrodes.
5. The earthed point of the source, or an artificial neutral.

Protective Conductors are divided in to 4 main categories in BS7671

1. Earthing conductor.
2. Main equipotential bonding conductor.
3. Supplementary bonding conductor.
4. Circuit Protective Conductor.

Sizing of Protective Conductors BS7671

543 -01-01 states that the cross sectional area of every protective conductor , other than an equipotential conductor, shall be:

1. Calculated in accordance with Regulation 543 – 01 – 03, or
2. Selected in accordance with Regulation 543 – 01 – 04.

So if the SWA were to be used as a protective conductor, other than an equipotential bonding conductor, it would have to be suitably sized using either the adiabatic equation in 541-01-03 or selected from the appropriate tables.

The use of SWA as a Protective Conductor BS7671

The permitted types of protective conductor are listed in 543-02-02 and SWA is identified in sub section (v) as:

A metal covering, for example, the sheath, screen, or armouring of a cable.

It can therefore be verified that the SWA can be used as a protective conductor in compliance with BS7671.

However there are conditions on the use of SWA as a protective conductor defined in BS7671.

1. It must be adequately sized to meet the requirements of section 543-01-01.
2. If the armour is used as a CPC then any accessories have to be connected to the associated enclosure’s earth terminal by a separate CPC (flying lead) to comply with 543-02-07.
3. If the SWA is used as a main equipotential conductor other than on a PME system it must have a CSA of not less than half the cross sectional area of the associated earthing conductor and not less than 6mm² to comply with 547-02-01. If the installation is PME then the CSA of the SWA must comply with table 54H. If the conductor material is other than copper the material has to have the equivalent conductance to copper.
4. Where a number of installations have separate earthing arrangements any protective conductors common to these have to be suitably sized to carry the maximum current likely to flow through them OR insulated from the other installation at one end to comply with 542-01-09.
5. If the SWA is to be used as a combined CPC and main bonding conductor it must meet the requirements of both 547- 02-01 and 543-01.

Is the wire armouring an exposed conductive part?

The wire armouring is steel and therefore is conductive. However the steel is covered by an exposed oversheath of insulation so is not exposed. The cable is terminated on most installations with brass glands which are conductive. These parts are therefore exposed conductive parts but these may also be covered with PVC shrouds.

The function of the armouring is to protect the cable against mechanical damage and to allow the cable to be run out of safe zones. Should a sharp conductive object such as a drill bit or garden fork penetrate the cable it is critical that the armouring is connected to earth to enable the supply to be automatically disconnected by the circuit protective device under this fault condition.

The use of bonding clamps as an alternative to glands.

Bonding clamps are designed for clamping on to solid pipes. The force required to make a reliable tight joint on to a SWA cable would effectively deform the cable and may loosen over time due the continued deformation of the cable.

Cross sectional area and conductivity of SWA.

The CSA of the armouring of various SWA cables is set out in tables D9, D10A and D10B of IEE GN1. These are for thermoplastic PVC cables operating at 70⁰C, 90⁰C thermosetting cables operating at 90⁰C and 90⁰C thermosetting cables operating at 70⁰C respectively. These tables also very usefully indicate where these cables meet with the requirement of table 54G of BS7671 for the adequacy of the CPC CSA.

I have produced below the information for thermoplastic and thermosetting cables operating at 70⁰C.

The figures shown in brackets do not meet the requirements of table 54G however if the adiabatic equation for the prospective fault current and the circuit protection device used is calculated then the armour might comply with 543-01-03. If the armour is found to be undersized then a full sized separate CPC must be provided.

Table for 70⁰C Thermoplastic PVC SWA cables.

Table for 90⁰C Thermosetting SWA cables operating at 70⁰C.

Terminating the cable ends of SWA cables.

BS7671 has a fundamental requirement set out in regulation 133-01-04 for every electrical joint and connection shall be of proper construction as regards conductance, insulation, mechanical strength and protection.

This requirement would preclude the termination of the cable ends of SWA with bonding clamps for the reason given above. It would also preclude the termination of the cable by inserting it into an enclosure without a gland as the steel armouring earth continuity could not be reliable.

Cable manufacturers supply and recommend the termination of their SWA cables in glands correctly selected for the individual size of the particular cable. These glands are supplied for internal use and alternative exterior glands rated at IP66 for external use.

The manufacturer’s gland kits are provided with suitably sized earth rings which are commonly known as “Banjos”. These earth rings are used to enhance the contact surface area of the gland and are also provided with a bolt hole for connection of an auxiliary CPC.

The cable glands can be directly used without the earth ring in the same manner as conduits and MICC cables are terminated in metal enclosures. As with conduits and MICC cables the paint around the enclosure hole must be removed to expose bare metal. The gland lock nuts must then be suitably tightened to maintain conductivity.

Some enclosures are provided with removable gland plates and in these circumstances the earth continuity relies on the gland plate fixing screws. It is recommended in these circumstances that the earth ring is used with a suitably sized CPC connected to the main earth bar. This is never done with conduit or MICC in my experience which also relies on these fixing screws for earth continuity. An alternative would be to drill the gland plate and bolt a CPC to it connected to the main earth bar.

where an SWA cable enters a plastic enclosure then an earth ring would be needed to maintain earth continuity.

It goes without saying that the steel wires of the armouring should all enter the tapered socket of the cable gland and the gland nut should be adequately tightened.

In the same way as the regulations do not require a separate CPC to be used with metal conduits it would seem good practice to always use an earth ring. This ring to be separately bolted to the enclosure and a CPC with a crimped eyelet connected to this bolt. The CPC then connected to the earth terminal of the enclosure. If the enclosure is outside or exposed to moisture then it would be preferable to place the earth ring on the inside of the enclosure. This will permit the paint or other coating to be removed under the ring without compromising the environmental protection for the enclosure.

Environmental Conditions

There is a general requirement for all electrical equipment to be suitable for the environmental conditions prevailing for that installation set out in BS7671. There is also an additional requirement for earthing systems set out in 542-01-07 which requires, “ they are adequately robust or have additional mechanical protection appropriate to the assessed conditions of external influence”.

I have found one reference in IEE GN7 that would preclude the use of the armouring as a CPC when SWA cables are used. This is in Marinas and the guidance states, “Due to the possibility of corrosion, the galvanised steel armouring of cables must not be used wholly or in part as a circuit protective conductor (cpc) for the floating section of marinas. A separate protective conductor should be used which, when in accordance with Regulation 543-01-02 can be common to several circuits if necessary. The armour must still, however, be connected to protective earth”.

If the SWA cable ends are terminated outside or in areas where water is present then the exterior IP66 glands should be used.

TNCS (PME) Installations

Where the supply company will not permit the export of the means of earthing to the supplied premises outside of those premises then special precautions will need to be taken for SWAs supplying remote buildings or equipment outside the supplied premises.

The reason for this restriction is to prevent the danger of exposed conductive parts and extraneous conductive parts connected to the installation outside the main equipotential zone becoming live in the event of the loss of the neutral under fault conditions. Also with long cable runs their will be a potential difference between the supplied earth from the neutral terminal and the general mass of earth.

In these circumstances it is preferred to connect the steel armouring of the SWA to earth at the main supplied premises and insulate the armouring at the remote end of the cable. This allows the SWA cable to be protected by the circuit protection device that is protecting the phase conductor(s) of the cable. At the remote building the SWA is terminated in a plastic box and only the live conductors are then connected to the remote installation. The remote installation is converted to a TT system with a suitably selected RCD main switch and the provision of an earth electrode.

It may also be possible with the consent of the supply company to extend the main equipotential zone to the remote building. This can be done by using the SWA armouring as a combined CPC and main bonding conductor. All extraneous metal work in the remote building is connected to a common terminal known as the Building Earth Marshalling Terminal (BEMT). The armouring must be sized to comply both with Regulations 547-02-01 and 543-01. In addition with a PME system there may be currents flowing normally in the protective conductors which may raise the temperature of the SWA cable. In these circumstances the cable will need to be derated to accommodate this temperature rise. An alternative may be to run a parallel PVC green/yellow cable of suitable size with the SWA. If this parallel CPC is buries then it would need to be a minimum of 16mm² to comply with Regulation 542-03-01 unless it is mechanically protected.

If the remote building has an alternative means of earthing then the SWA armour or separate CPC would need to be rated to permit the maximum current flow likely to comply with Regulation 542-01- 09.

Earth Loop Impedance

Where the measured value of earth loop impedance (Zs) at the end of a final circuit is found to be to high to achieve automatic disconnection by the circuit protection device in the required disconnection time Regulation 413-02-04 permits the use of supplementary bonding to achieve an acceptable measured value of Zs. This in my view is a compensatory measure for poor initial design of the circuit and incorrect selection of the cable. If the cable was correctly selected at the design stage with due regard to the required value of Zs for the final circuit, the Zs of the distribution board, the R1 + R2 calculated value for the size and length of cable and any temperature correction then compensatory measures would not be required. If supplementary bonding is required then the use of a spare core of an SWA cable could be used or an additional CPC run in parallel with the cable.

Supplementary CPCs.

Where it is determined that a selected cable size will not provide sufficient CSA for the CPC a supplementary CPC can be run in parallel with the SWA cable. This CPC should be adequately sized to handle the full potential earth fault current not just to provide sufficient additional capacity to the SWA armour to meet the required CSA. This is required as the currents flowing under fault conditions would not be equally distributed over the cables due to differences in impedance.

Conclusion

The use of internal cores, of both thermoplastic and thermosetting SWA cables, as a CPC and/or the use of separate parallel CPCs are not required for SWA cables to comply with BS7671 provided.

1. The operating temperature of the cable does not exceed 70⁰C.
2. The CSA of conductor cores does not exceed 95mm².
3. The cable is not installed in the floating section of any marina.
4. The cable is correctly selected for the correct value of R1 + R2 for the circuit protection device protecting the cable.
5. The cable does not connect different installations together which have separate means of earthing unless sized for the potential earth fault current.
6. The cable is not used as a combined CPC and bonding conductor on a PME installation unless suitably sized.
7. The cables are properly terminated in correctly sized manufactures brass glands selected for the external influences prevailing.
8. Where a removable gland plate is present on the enclosure to which the cable is attached the earth ring ( banjo) supplied with the gland is used and is connected to the earth terminal in the enclosure with a separate CPC. This CPC terminated in an eyelet to a bolted connection to the earth ring.
9. Any protective coating on the enclosure surface is removed under the contact surfaces of the gland and associated earth ring to expose bare metal.
10. All the wires of the armouring enter the gland and the gland nut is adequately tightened. The cable is adequately supported up to the gland with cable cleats to prevent mechanical strain on the gland.

References

1. BS 7671:2001 amended to 2004 Requirements for Electrical Installations.
2. IEE Guidance Note 1 Selection and Erection.
3. IEE Guidance Note 7 Special Locations.

Thanks to: ©John Peckham 2006

Places a legal responsibility on employers and employees, as duty holders, to ensure that electrical systems used at work under their control are safe.

Legal Requirements

To achieve compliance with the legal requirements of the Electricity at Work Regulations 1989 requires proof that an electrical system is safe, which involves amongst other things, proper inspection and testing of a system by competent people and the creation and maintenance of records.

Electricity at Work Regulations 1989 is law in the United Kingdom.

Electricity At Work Regulations 1989 (EAWR)

The regulations as stated below are an overview of the UK regulations. For a comprehensive guide please refer to the latest version of the HSE document "Memorandum of Guidance on the Electricity At Work Regulations" - available from HMSO or technical bookshops.

PART I

INTRODUCTION

Citation and commencement
1. These Regulations may be cited as the Electricity at Work Regulations 1989 and shall come into force on 1st April 1990.

• "approved" means approved in writing for the time being by the Health and Safety Executive for the purposes of these Regulations or conforming with a specification approved in writing by the Health and Safety Executive for the purposes of these Regulations;
  "circuit conductor" means any conductor in a system which is intended to carry electric current in normal conditions, or to be energised in normal conditions, and includes a combined neutral and earth conductor, but does not include a conductor provided solely to perform a protective function by connection to earth or other reference point;
  "conductor" means a conductor of electrical energy;
  "danger" means risk of injury;
  "electrical equipment" includes anything used, intended to be used or installed for use, to generate, provide, transmit, transform, rectify, convert, conduct, distribute, control, store, measure or use electrical energy;
  "firedamp" means any flammable gas or any flammable mixture of gases occurring naturally in a mine;
  "injury" means death or personal injury from electric shock, electric burn, electrical explosion or arcing, or from fire or explosion initiated by electrical energy, where any such death or injury is associated with the generation, provision, transmission, transformation, rectification, conversion, conduction, distribution, control, storage, measurement or use of electrical energy;
  • (a) any coal mine; or
    • (i) there has occurred below ground an ignition of firedamp; or
      • "system" means an electrical system in which all the electrical equipment is, or may be, electrically connected to a common source of electrical energy, and includes such source and such equipment.
      (ii) more than 0.25% by volume of firedamp is found on any occasion at any place below ground in the mine;
    (b) any other mine in which-
  "safety-lamp mine" means-
  (a) a numbered regulation or Schedule is a reference to the regulation or Schedule in these Regulations so numbered;
  (b) a numbered paragraph is a reference to the paragraph so numbered in the regulation or Schedule in which the reference appears.
Interpretation
2.—(1) In these Regulations, unless the context otherwise requires-
(2) Unless the context otherwise requires, any reference in these Regulations to-

• (a) employer and self-employed person to comply with the provisions of these Regulations in so far as they relate to matters which are within his control; and
  (b) manager of a mine or quarry (within in either case the meaning of section 180 of the Mines and Quarries Act 1954 to ensure that all requirements or prohibitions imposed by or under these Regulations are complied with in so far as they relate to the mine or quarry or part of a quarry of which he is the manager and to matters which are within his control.
  (a) to co-operate with his employer so far as is necessary to enable any duty placed on that employer by the provisions of these Regulations to be complied with; and
  (b) to comply with the provisions of these Regulations in so far as they relate to matters which are within his control.
Persons on whom duties are imposed by these Regulations

3.—(1) Except where otherwise expressly provided in these Regulations, it shall be the duty of every-

(a) employer and self-employed person to comply with the provisions of these Regulations in so far as they relate to matters which are within his control; and

(b) manager of a mine or quarry (within in either case the meaning of section 180 of the Mines and Quarries Act 1954 to ensure that all requirements or prohibitions imposed by or under these Regulations are complied with in so far as they relate to the mine or quarry or part of a quarry of which he is the manager and to matters which are within his control.

(2) It shall be the duty of every employee while at work-

(a) to co -operate with his employer so far as is necessary to enable any duty placed on that employer by the provisions of these Regulations to be complied with; and

(b) to comply with the provisions of these Regulations in so far as they relate to matters which are within his control.

GENERAL

Systems, work activities and protective equipment
4.—(1) All systems shall at all times be of such construction as to prevent, so far as is reasonably practicable, danger.

(2) As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger.

(3) Every work activity, including operation, use and maintenance of a system and work near a system, shall be carried out in such a manner as not to give rise, so far as is reasonably practicable, to danger.

(4) Any equipment provided under these Regulations for the purpose of protecting persons at work on or near electrical equipment shall be suitable for the use for which it is provided, be maintained in a condition suitable for that use, and be properly used.

Strength and capability of electrical equipment
5. No electrical equipment shall be put into use where its strength and capability may be exceeded in such a way as may give rise to danger.
• (a) mechanical damage;
  (b) the effects of the weather, natural hazards, temperature or pressure;
  (c) the effects of wet, dirty, dusty or corrosive conditions; or
  (d) any flammable or explosive substance, including dusts, vapours or gases,
Adverse or hazardous environments
6. Electrical equipment which may reasonably foreseeably be exposed to-shall be of such construction or as necessary protected as to prevent, so far as is reasonably practicable, danger arising from such exposure.
• (a) be suitably covered with insulating material and as necessary protected so as to prevent, so far as is reasonably practicable, danger; or
  (b) have such precautions taken in respect of them (including, where appropriate, their being suitably placed) as will prevent, so far as is reasonably practicable, danger.
Insulation, protection and placing of conductors
7. All conductors in a system which may give rise to danger shall either-
Earthing or other suitable precautions
8. Precautions shall be taken, either by earthing or by other suitable means, to prevent danger arising when any conductor (other than a circuit conductor) which may reasonably foreseeably become charged as a result of either the use of a system, or a fault in a system, becomes so charged; and, for the purposes of ensuring compliance with this regulation, a conductor shall be regarded as earthed when it is connected to the general mass of earth by conductors of sufficient strength and current-carrying capability to discharge electrical energy to earth.
Integrity of referenced conductors
9. If a circuit conductor is connected to earth or to any other reference point, nothing which might reasonably be expected to give rise to danger by breaking the electrical continuity or introducing high impedance shall be placed in that conductor unless suitable precautions are taken to prevent that danger.
Connections
10. Where necessary to prevent danger, every joint and connection in a system shall be mechanically and electrically suitable for use.
Means for protecting from excess of current
11. Efficient means, suitably located, shall be provided for protecting from excess of current every part of a system as may be necessary to prevent danger.
• (a) cutting off the supply of electrical energy to any electrical equipment; and
  (b) the isolation of any electrical equipment.
Means for cutting off the supply and for isolation
12.—(1) Subject to paragraph (3), where necessary to prevent danger, suitable means (including, where appropriate, methods of identifying circuits) shall be available for-
(2) In paragraph (1), "isolation" means the disconnection and separation of the electrical equipment from every source of electrical energy in such a way that this disconnection and separation is secure.

(3) Paragraph (1) shall not apply to electrical equipment which is itself a source of electrical energy but, in such a case as is necessary, precautions shall be taken to prevent, so far as is reasonably practicable, danger.

Precautions for work on equipment made dead
13. Adequate precautions shall be taken to prevent electrical equipment, which has been made dead in order to prevent danger while work is carried out on or near that equipment, from becoming electrically charged during that work if danger may thereby arise.
• (a) it is unreasonable in all the circumstances for it to be dead; and
  (b) it is reasonable in all the circumstances for him to be at work on or near it while it is live; and
  (c) suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury.
Work on or near live conductors
14. No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless-
Working space, access and lighting
15. For the purposes of enabling injury to be prevented, adequate working space, adequate means of access, and adequate lighting shall be provided at all electrical equipment on which or near which work is being done in circumstances which may give rise to danger.

Persons to be competent to prevent danger and injury
16. No person shall be engaged in any work activity where technical knowledge or experience is necessary to prevent danger or, where appropriate, injury, unless he possesses such knowledge or experience, or is under such degree of supervision as may be appropriate having regard to the nature of the work.

---

 

REGULATIONS APPLYING TO MINES ONLY

Provisions applying to mines only
17.—(1) The provisions of regulations 18 to 28 and Schedule 1 shall apply to mines only; and the provisions of that Schedule shall have effect in particular in relation to the use below ground in a coal mine of any film lighting circuit (as defined by paragraph 1 of that Schedule) at or in close proximity to a coal face.

(2) Expressions to which meanings are assigned by the Mines and Quarries Act 1954 shall, unless the contrary intention appears, have the same meanings in regulations 18 to 27 and Schedule 1.

Introduction of electrical equipment
18. Before electrical equipment (other than equipment approved for the purposes of regulation 20(1)) is first introduced into any underground part of a safety-lamp mine to which the Coal and Other Mines (Surveyors and Plans) Regulations 1956 apply, the manager shall submit to an inspector a copy of the ventilation plan required to be kept for that part by regulation 9 of those Regulations, on which the intended locations of that equipment shall be shown, together with a copy of any schematic diagram relating to that part prepared for the purposes of regulation 24(1).
• (a) equipment of a kind approved for that purpose;
  (b) equipment approved pursuant to regulation 20(1);
  (c) equipment the use of which was lawful in such zones immediately before the coming into force of these Regulations;
  (d) equipment which has received a certificate of conformity or a certificate of inspection in accordance with Council Directive 82/130/EEC on the approximation of the laws of the Member States concerning electrical equipment for use in potentially explosive atmospheres in mines susceptible to firedamp, as adapted to technical progress by Commission Directive 88/35/EEC:
  (e) equipment such as is specified in regulation 21(2);
  (f) equipment which is not capable of producing incendive electrical sparks in normal use; or
  (g) electrically- powered equipment not permanently installed in the mine but required occasionally for monitoring, testing, recording and measurement, and used where the concentration of firedamp is 0.8% by volume or less in accordance with suitable rules drawn up by the manager to ensure that danger will not thereby arise, which rules shall in particular include provision for personal supervision of that equipment by a competent person and testing for firedamp when it is in use;
Restriction of equipment in certain zones below ground
19.—(1) At every safety-lamp mine containing any zones below ground in which firedamp whether or not normally present is likely to occur in a quantity sufficient to indicate danger, there shall be prepared a suitable plan identifying such zones.

(2) Electrical equipment shall not be energised in such zones unless it is-and any lights which conform with this paragraph shall be permitted lights in any mine such as is specified in paragraph (1).

• (a) cut off the supply of electricity to any electrical equipment situated at the place where the said concentration was detected; or
  (b) (where this is not possible) take all reasonably practicable steps to make such equipment safe; or
  (c) (if the taking of the measures specified in sub-paragraphs (a) and (b) above does not fall within the scope of his normal duties) report the matter to an official of the mine who shall ensure that those measures are taken;
Cutting off electricity or making safe where firedamp is found either below ground or at the surface
20.—(1) Where any person at a mine detects firedamp in a concentration exceeding 1.25% by volume in the general body of the air either below ground at that mine or at any place on the surface thereat where any exhauster in a firedamp drainage system is installed, firedamp is monitored or its heat content measured, he shall forthwith-except that the provisions of sub-paragraphs (a) to (c) above shall not apply if the electrical equipment is approved for the purpose of remaining energised in such circumstances or (in the case of a safety-lamp mine) is electrical equipment such as is specified in regulation 21(2).

(2) If the supply of electricity to electrical equipment is cut off or the equipment made safe in accordance with paragraph (1), it shall remain in that condition until the senior official on duty at the mine having determined that it is safe to do so, directs that such precautions are no longer necessary.

(3) If the supply of electricity to electrical equipment is cut off or the equipment made safe in accordance with paragraph (1), details of the time, duration and location shall be recorded.

Approval of certain equipment for use in safety-lamp mines
21.—(1) Subject to paragraph (2), no electric safety-lamp, gas detector, telephone or signalling equipment or other equipment associated therewith or required for the safety of persons shall be taken or used below ground at any safety-lamp mine unless it is equipment which has been approved pursuant to regulation 20(1) or (in the case of electric safety-lamps) is of a type for the time being approved pursuant to section 64(2) of the Mines and Quarries Act 1954.

(2) Nothing in paragraph (1) shall prevent the taking or use below ground at any safety-lamp mine of any electrical equipment which was, before the coming into force of these Regulations, approved pursuant to regulations 20 and 21A of the Coal and Other Mines (Electricity) Regulations 1956.

Means of cutting off electricity to circuits below ground
22. At every mine at which electrical equipment which may give rise to danger is installed below ground and is supplied from a power source at the surface of the mine, switchgear shall be provided at the surface for cutting off the supply of current to that equipment, and adequate provision shall be made for the operation of that switchgear, including such means of communication as will, so far as is reasonably practicable, enable the switchgear to be operated in case of danger.
Oil-filled equipment
23. Electrical equipment using oil as a means of cooling, insulation or arc suppression shall not be introduced below ground at a mine.
• (a) be prepared and kept in the office at the mine; and
  (b) show the planned settings of any circuit electrical protective devices.
Records and information
24.—(1) Suitable schematic diagrams of all electrical distribution systems intended to be operated at the mine (other than those operating at a voltage not exceeding 250 volts) shall, so far as is reasonably practicable-
(2) Copies of such portions of the schematic diagrams prepared pursuant to paragraph (1) as are necessary to prevent danger and which show at least those parts of the electrical system which are served by switchgear operating at a voltage in excess of 250 volts shall be displayed at each place where such switchgear is installed.

(3) Plans on a suitable scale shall be kept in the office at the mine showing, so far as is reasonably practicable, the position of all permanently installed electrical equipment at the mine supplied at a voltage in excess of 250 volts.

Electric shock notices
25. Where, at any place at a mine, electric arc welding is taking place or electrical energy is being generated, transformed or used at a nominal voltage in excess of 125 volts a.c. or 250 volts d.c., a notice shall be displayed in a form which can be easily read and understood and containing information on the appropriate first-aid treatment for electric shock and details of the emergency action to be taken in the event of electric shock.
Introduction of battery-powered locomotives and vehicles into safety-lamp mines
26. No locomotive or vehicle which uses an electrical storage battery, either partly or wholly, as a power source for traction purposes shall be introduced below ground at a safety-lamp mine unless it is an approved locomotive or vehicle.
Storage, charging and transfer of electrical storage batteries
27. At any mine in which electrical storage batteries are used below ground, those batteries shall, so far as is reasonably practicable, be used, stored, charged and transferred in a safe manner.

 

Disapplication of section 157 of the Mines and Quarries Act 1954
28. Section 157 of the Mines and Quarries Act 1954 (which provides a defence in legal proceedings and prosecutions in certain circumstances) shall not apply in relation to any legal proceedings or prosecutions based on an allegation of a contravention of a requirement or prohibition imposed by regulations 18 to 27 or by or under Schedule 1.

 

MISCELLANEOUS AND GENERAL

Defence
29. In any proceedings for an offence consisting of a contravention of regulations 4(4), 5, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 25, it shall be a defence for any person to prove that he took all reasonable steps and exercised all due diligence to avoid the commission of that offence.
• (a) any person;
  (b) any premises;
  (c) any electrical equipment;
  (d) any electrical system;
  (e) any electrical process;
  (f) any activity,
  (a) the conditions, if any, which it proposes to attach to the exemption; and
  (b) any other requirements imposed by or under any enactment which apply to the case,
Exemption certificates
30.—(1) Subject to paragraph (2), the Health and Safety Executive may, by a certificate in writing, exempt-or any class of the above, from any requirement or prohibition imposed by these Regulations and any such exemption may be granted subject to conditions and to a limit of time and may be revoked by a certificate in writing at any time.

(2) The Executive shall not grant any such exemption unless, having regard to the circumstances of the case, and in particular to-it is satisfied that the health and safety of persons who are likely to be affected by the exemption will not be prejudiced in consequence of it.

Extension outside Great Britain
31. These Regulations shall apply to and in relation to premises and activities outside Great Britain to which sections 1 to 59 and 80 to 82 of the Health and Safety at Work etc. Act 1974 apply by virtue of Articles 6 and 7 of the Health and Safety at Work etc. Act 1974 (Application outside Great Britain) Order as they apply within Great Britain.
• (a) the master or crew of a sea-going ship or to the employer of such persons, in relation to the normal ship-board activities of a ship's crew under the direction of the master; or
  (b) any person, in relation to any aircraft or hovercraft which is moving under its own power.
Disapplication of duties
32. The duties imposed by these Regulations shall not extend to-
Revocations and modifications
33.—(1) The instruments specified in column 1 of Part I of Schedule 2 are revoked to the extent specified in the corresponding entry in column 3 of that Part.

(2) The enactments and instruments specified in Part II of Schedule 2 shall be modified to the extent specified in that Part.

(3) In the Mines and Quarries Act 1954, the Mines and Quarries (Tips) Act 1969 and the Mines Management Act 1971, and in regulations made under any of those Acts, or in health and safety regulations, any reference to any of those Acts shall be treated as including a reference to these Regulations.

 


Signed by order of the Secretary of State.

Patrick Nicholls