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.
