Electrical services,testing,contracting,design

 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 moulded 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 work
stations 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 specialists
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 high
level 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 of
luminaires 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 they
can 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 unlimited
number 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 an
unsuspecting 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 (BS
EN 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 8A
Final circuits using BS 1363 socket-outlets and connection units
Minimum conductor cross-sectional area
Type of circuit
Overcurrent protective device Rating A Copper Conductor thermoplastic or thermosetting nsulated cables mm2 CopperConductor mineral insulatecables mm2
Maximum floor area served m2
1 2 3 4 5 6
A1 Ring 30 or 32 2.5 1.5 100
A2 Radial 30 or 32 4 2.5 75
A3 Radial 20 2.5 1.5 50
It 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 a
suitably 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 develop
other 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.

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 brain
washed 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 buildings
As well as Domestic
At this point I would like to make it clear that I am not against ring circuits, there is a
place for them in modern installations provided they are properly designed in
accordance with BS 7671, carefully installed and tested as detailed in IEE Guidance
notes 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 – 433-02-04
BS 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 is
often impractical to apply. This regulation requires the load to be distributed around
the circuit so that the current in any part of the ring does not exceed the installed
rating of the cable. This means that in a circuit intended to supply a washing
machine, tumble dryer and a dishwasher the points need to be wired so that the load
current 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 washing machine, 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 543-02-09
Regulation 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 a
metal 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 505
A 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 10
A test shall be made to verify the continuity of all conductors
(including the earth-continuity conductor) of every ring circuit.
No test methods given
IEE Wiring Regulations – 15th Edition 1981 Regulation 613-2
A test shall be made to verify the continuity of all conductors (including the protective
conductor) 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 and
became 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 713-03
A test shall be made to verify the continuity of all conductors (including the protective
conductor) 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 phase
loop 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 each
point twice takes too long.
None of the test results schedules that I have seen provide for the ‘interconnected
conductors’ 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.