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When is a Ring Main not a Ring Main?
Ring main is a term which has been used for years, and will continue to be used for many more years, but it is incorrect, it’s just easy to say!
The correct terminology for Ring Main is either Final Ring Circuit or Ring Circuit, however, now you know that we will continue to refer to it in the most common parlance as seen all over the internet.
Please also see our project on the New Wiring and Cable Colours. Before attempting any electrical work at home, please read our project called Part P Building Regulations and also make sure you have isolated any circuit you are working on.
What is a Ring Main or Ring Final Circuit or Final Circuit?
A ring main, or final circuit, is exactly what it says on the tin. It is a ring of cables, usually 2.5mm carrying twin and earth wires, circling your home, carrying the mains electricity to sockets on the way. It gets the power from the consumer unit and delivers it to the sockets.
How Does a Final Ring Circuit or Ring Main Work
As both ends of the ring are connected to the same terminals at the consumer unit, the current runs in both directions imposing less of a load on the cables. Electricity loses power over long lengths of cable and trying to put too much power through a cable which is not designed for it is dangerous, so a ring main delivers power from both ends to keep the load as light as possible.
The other type of circuit used to power your home is a radial circuit. They are not so common in the UK but are used extensively abroad as the ring main, or final ring circuit does have it’s drawbacks.
The radial circuit can be turned into a ring circuit by completing the wiring back to the consumer unit and similarly the ring main, or final circuit ring can be turned into two radial mains by removing a section of the ring.
This is one of the failure points of a ring main or final ring circuit which is identified below in the pros and cons of using a ring or radial circuit.
If you would like to find out more about these circuits, see our project on radial circuits.
How Can I Tell if my House has Radial Circuits or Ring Mains (Final circuits)
We would like to thank one of our forum members for answering this question in our busy electrical forum and you can see the answers to many more questions there.
Identifying a radial circuit and a final ring circuit requires a test. A sparky (electrician) will disconnect the wires in the consumer unit and test continuity between the two cables on the live and return terminals.
Sockets on a ring main have at least two sets of wires connected to them, but spurs may also have two sets of wires and so do sockets on a radial circuit, all except the last one anyway so counting cables on the back of sockets is not a safe way to identify a ring circuit or ring main.
Ring circuits are normally fed with a 30 or 32 amp fuse or MCB, but if feed is supplied through a 4mm cable then the spurs could also be feed with 30 or 32 amp fuse or MCB.
If the circuit was originally a ring main but this has become broken and is now a spur or radial main then it could be fed with 2.5mm and 32 amp fuse.
Even though the sockets are connected to two cables or 2.5mm and supplied by a 32 amp fuse or MCB it cannot be guaranteed that it is a ring main or final circuit.
In short if you cannot correctly test whether the circuit you have is a ring main or a radial circuit then you should not, under any circumstances be working on it. The UK is the only country in the world to work with Ring Mains, or Final Ring Circuits and without the correct testing equipment and knowledge of procedures it is impossible to tell the difference.
Testing for a Ring or Radial Circuit
As we all know, electricity is dangerous and potentially lethal, so you have to have the necessary knowledge in order to work with it.
If you understand this paragraph then you are able to test yourself. If you do not, leave it alone.
Put two block connectors on the two cables feeding a socket and tested both blocks with both earth loop and PSC to ensure it is part of a ring main before adding a spur
Restrictions on a Ring Main or Ring Circuit
There are still restrictions on how much power and for how long, a ring main or final ring circuit may carry. This is reflected in the maximum distance a cable may be used for and the fuse rating it is given. Please see cable length restrictions below for more information.
A separate ring main is usually installed on every floor of a given property to make sure things are kept safe and it is only when, for example, a spur socket (additional socket) is added on an upstairs ring main, to feed a socket or light on a downstairs circuit, that things can get tricky. For the rules that govern how tis can be dne, please see our Part P project linked to above.
Using a ring or radial circuit to power lighting requires the use of a fused spur which is fused independently of the circuit the power is coming from. You can see more about how a switched or fixed fused spur works in our project here.
A switched fused spur is also used when connecting a cooker hob, dishwasher, washing machine or fridge to the circuit. It allows the appliance to be switched on and off from a position above the worktop, or at least a more easily reachable position than the socket they are plugged into (which is normally located below worktops and behind the appliance). The switched fused spur interrupts the socket and allows it to be switched on and off.
Cable Used for a Ring Main or Final Ring Circuit
A ring main uses 2.5mm cable comprising of a live, neutral and earth. This is called two core and earth cable. The 2.5mm is the measurement of the cross sectional area of the cables.
An example of this cable type can be seen below and shows the live, neutral and earth wires.
Floor Area for a Ring Main or Final Ring Circuit
The floor area a ring main serves is also governed. This is because the regulation people have some idea of how much power and lighting we can expect to use in such an area. The maximum area for a ring main is 100 square meters.
An average house has a footprint of about 64-70 square meters so this allows for the continuation of the ring into a porch or garage etc. The ring main must be protected by a 30amp fuse if it is on a cartridge fuse board, or a 32amp MCB fuse.
The cable itself can be up to 60 meters long if it is protected by a cartridge fuse and 50 meters long if protected by an MCB.
There is no limit to the number of sockets you can have on a ring main but there is a limit to the number of spurs you can have from those sockets or from the wiring between them. If you would like to know how to add a spur to an existing ring main, see our project on adding an extra socket.
It is also possible to extend a ring main if you need to. For help and information on how to do this, please see our extending a ring main project here.
Once you have identified whether you have a ring main (final ring circuit) or a radial circuit) you can add only one spur socket for every socket on the final ring. Be very careful and test properly to see if any other sockets have been added to the circuit by means of a junction box, such as the one below.
Cooker and Electric Shower Circuits
Units or appliances which use a lot of power, like cookers and showers, must be installed on their own circuits so please check the appliances you are considering using on your ring main.
It is also a regulation that any socket which is capable of being used to supply power outside of the house is protected by an RCD (residual current device). Most modern consumer units will provide this protection but again it is vital that you get a qualified electrician to check and approve any installation you may consider.
Length of Cable Limitations in Ring and Radial circuits
Please also check the rules very carefully for ring mains and radial circuits. You are limited in the length of cable you are allowed to use in both circuits and long spurs could make you exceed the limit.
If this is the case you are asking the circuit to use much more energy than it is designed for. More energy = more heat and cables can catch fire. Part P of the new building regulations could involve a check on any additional circuitry by qualified electricians when you sell your home. This can affect your sale, you could be breaking the law and your house insurance may not be valid. Please be absolutely sure you know what you are doing and get all of your work checked by a qualified electrician.
There are also rules on how height sockets can be placed on walls and other surfaces. For regulations governing this, please ourSocket Height Regulations project page here.
Other helpful electrical projects that may be useful if you are looking into information on ring mains are as follows:
- Adding extra sockets
- Blowing light bulbs
- Consumer units
- connecting an electric shower
- dimmer switches
- earth bonding in bathrooms
- electrical safety
- Extending a ring main
- flexes wires and cables
- garden and outdoor lighting
- lighting circuit
- lights and switches
- Part P Building regulations
- radial circuit
- replacing a light fitting
- Stripping wires and cables
- wiring a junction box
- wiring in wall lights
If you like a read then there are quite a few decent reference books on electrics and domestic wiring, some that we would recommend can be seen below: