Most people have heard of the term ‘ring main’, although it’s not a terribly exciting topic for the masses. If you’re reading this, then the chances are you have a fault or require a new socket installation and you want to know more about how this sort of stuff works. This article aims to give some general information on the two types of socket installation you will come across in your home.
In the UK, most domestic socket outlets will be configured in a ring with a cable coming out of the main fuse box or Consumer Unit (CU) and visiting every socket in turn before returning back to the same fuse/breaker in the CU. A single ring can have an unlimited number of sockets directly connected (in theory) but should not exceed 100m2 of floor area. A small dwelling may only have one ring servicing all sockets while a larger property may have separate rings for different floors, extensions or for certain rooms such as kitchens and utility rooms where there may be several high-load appliances. By contrast, lighting circuits in the home are radial rather than ringed with a single cable leaving the CU and looping off each light fitting in turn until the last light in the chain where it terminates.
Sockets connected in a ring running from a single 30A fuse or 32A breaker in the consumer unit
Connecting sockets in a ring is pretty uncommon in the big wide world with only the United Arab Emirates and, to a lesser extent, Ireland connecting up their sockets in the same way as us Brits. Most other countries use the radial method for their socket outlets. By connecting the last socket in the chain back to the CU to form a ring, an alternative path is provided for the current so, in theory, loads on the left of the ring should be fed by the left cable while loads on the right should be fed from the right cable. In a radial circuit, the total load capacity needs to be supported by the whole cable throughout the installation.
Two radial socket circuits. Each would have its own protective fuse or breaker
Historically, we have the ring thing because after World War 2 Britain had to undertake a massive rebuilding programme and copper for cabling was in short supply. By splitting the socket loads in a ring formation, thinner copper cables could be used with fewer cables 'spidering' out from the consumer unit.
There are disadvantages to the ring method. If the ring is broken, you’re not likely to know about it as your sockets will continue to operate, however those thinner cables on one side of the ring may now be taking more load than they're safely rated to. Loads should also be balanced to ensure one side of a ring is not overloaded, however this doesn't happen in practice and heavy load items such as dishwashers, washing machines and dryers are often located in the same room with sockets that aren't split across the two sides of the ring. It is also possible to have a situation where a loose or dirty connection at the back of a socket means an appliance uses a live from one side of the ring and a neutral from the other side.
Because a ring has two paths, it typically has a higher number of socket outlets than a radial equivalent and a greater over-current protection of a 30A fuse or 32A breaker. Radial circuits fed by the same size cables tend to have fewer sockets and have lower rated 16A or 20A breakers depending on factors including the length of cabling and method of installation. Only if a radial socket circuit is being fed by cabling of (usually) 4mm2 or greater should it have a 32A breaker. Your average ring-fitted semi-detatched house in the UK may have two rings fed by wires with a csa of 2.5mm2 and each protected by a 32A breaker, whereas the same size property on the continent may have multiple radial circuits with each protected by 10, 16 or 20A breakers as appropriate. This makes for smaller consumer units in the UK and larger or more numerous consumer units required elsewhere.
It's for this reason British plugs contain 3, 5 or 13A fuses to protect an individual appliance rather than relying on the high rated circuit protective device. You’ve probably noticed American or continental plugs are smaller and less clunky than their UK counterparts and that’s because they don’t need to contain this user-accessible fuse. In the event of a faulty appliance, this local fuse may blow while the rest of the ring remains energised, while in countries without plugtop fuses a faulty appliance will trip the breaker and take out the whole radial circuit knocking out any other gadgets that may also be attached. This also means our American and European cousins can have a trickier task of tracking down which appliance is causing a trip. If there's no outward sign of a fault, they have to unplug everything on the circuit and reconnect things one at a time to see what upsets the breaker.
Ring circuits only tend to be used for socket outlets, while cookers, showers, water heaters and lighting all require their own radial circuit with their own circuit breaker and appropriate sized cabling. If you’re doing some DIY in the home, for goodness sake don’t try and hook up your new electric cooker or shower into your nearest socket ring!
Radial circuits with lower-rated breakers may not be suitable for certain applications. I met someone who was having building work done and was using the conservatory as a makeshift kitchen. The trouble was, there were only four sockets and a ceiling light in the conservatory, all running off a 16A radial circuit. The load of the lighting and fridge meant the additional load from the kettle or microwave was enough to trip the breaker. It wasn't that the sockets in the conservatory were unsafe or faulty, but rather that the circuit just wasn't designed to handle the simultaneous connection of high load motors, compressors and heating elements in that particular room.
If you have a damaged ring and repair is too difficult or impractical, or you want to remove an internal wall which contains sockets and a ring return path, it may be possible to cut the existing ring into separate lower-rated radial circuits. If a new socket circuit is required, for example in an extension, either ring or radial options can be considered. Either option is valid.
When it comes to running spurs off the ring, what usually happens is a single cable with cores of a CSA of 2.5mm2 is used to supply the spur. In that eventuality, the regulations permit only one single or twin gang socket be fitted. A single spur should not have further spurs run from it as the cable may become overloaded. If more than one outlet is requried on a spur, then a fused connection unit should be fitted first to prevent the load of all subsequent sockets/appliances from ever exceeding 13A and overloading the cable.
My crystal ball appears to be a little unreliable when I use it to try and guess the results of the EuroMillions, however gazing into it now I wouldn’t be surprised if the UK started following the rest of the world eventually with new builds utilising multiple radial socket circuits instead of rings. I also wouldn’t be terribly surprised to see hybrid UK/EU sockets appearing in such installations, capable of accommodating either a UK BS1363 fused plug or an EU style ‘Schuko’ unfused plug in order to increase harmonisation with the EU and improve standardisation.
Hybrid sockets already exist such as the one pictured above which is capable of accepting all sorts of wierd and wonderful plugs from around the world, however such sockets are only really suitable on circuits that have lower rated protective devices to protect appliances that are connected by unfused plugs. Care should also be taken to avoid connecting a 110V appliance to a 230V outlet via this type of socket.
I guess we'll just have to watch this space to see what future revisions of the standards demand.
AFF7