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There are lots of electrical questions that assume everyone is in the USA, so what is different for people that are in the UK?

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We can add this for all countries to make the topic even wider. – Toon Krijthe Sep 17 '10 at 11:36
Not these days all wires in Romex cable are the same size. Older outdated used smaller bare wire or green wire. I have a house that has small ground wires but I will never reuse that wire if I do a new install in an older building. Rule of thumb always use larger than needed. I will never use number 14 in my house period. You never know when your heat goes out and need to use a space heater. Always ready and never sorry. – user34431 Mar 8 '15 at 21:30
Actually new regkations state that a left and ring ring be used as if one rjng fails, you have power both upstairs and downstairs. – user37555 May 15 '15 at 7:56
up vote 5 down vote accepted

Many, many things.

First up, voltage. For historical reasons just about every domestic installation in the UK uses the same European standard voltage of 230V for every socket. In turn, almost all sockets used indoors are the same size and shape and deliver the same maximum current. (Some farms have three-phase 415V supply, but I don't think that's often run to the house itself...!)

Just in itself that introduces a whole level of complexity as the higher voltage is much keener on using a human being to find its way to earth.

Secondly, current. UK domestic power sockets are all rated at 13A, whereas in the US there's typically different sockets for different kinds of jobs. However, these sockets are joined in a "ring main" which is typically rated at 32A in total for all the sockets on the ring: so in theory connecting live and neutral on a ring main can deliver 230V * 32A = 7.3kW.

Makes for a nice bang. So it's wise to be careful.

Power in the UK is distributed from the supply company's meter to a "consumer unit" (these days, RCDs and circuit breakers) from whence the ring mains for sockets, lights and heavy equipment are powered. Like sockets, breakers are double-pole. The power company generally only provides a single-phase supply from their meter, it's an offence to tinker with anything upstream of that.

Earth is typically a ground spike combined with a connection to the water main (if it's metal) or the gas main. Separate earth runs need to be made to exposed metal fixtures such as basins or bathtubs.

Most houses have two ring mains, typically upstairs and downstairs, and for convenience most have an upstairs and a downstairs lighting ring. Electric cookers typically and water heaters (immersion heaters) typically get their own spurs. Lighting, the ring mains, and high-current spurs use different sizes of cable.

The UK has been described as one of the most heavily fused countries on earth. As the ring main can in theory deliver 32A to the socket, each appliance has its own fuse built into the plug. That, along with the higher voltage and current, is one reason why the UK has such big plugs. These fuses are (these days) clipped into their own holder which can be (reasonably) easily extracted without taking the plug apart; they come in 3A and 13A sizes.

There's more, much more: bathrooms and other wet areas have their own special restrictions, there's regulations about how wires can be joined together, how many sockets can be on a ring, the distance between sockets, the number of spurs permitted, and so on and so on. A two year apprenticeship is a good start, as is careful digestion of the Wiring Regulations.

What can be done by a DIYer? Notionally buildings regulations have always required a "Competent Person" to do any electical work. Since the introduction of Part P of building regulations a recognised contractor needs to inspect major work or work in bathrooms and kitchens.

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All US homes should have ~220V (between 220 and 240V) run, but it's split out as two separate ~110V legs for general outlets; 220V is used for electric clothes dryers, electric stoves, and some other larger appliances that require it. Some older homes might have 440V, as well (I know my grandmother's did). – Joe Jul 23 '10 at 21:36
Thanks Joe - I've updated my answer. – Jeremy McGee Jul 24 '10 at 20:20

In a typical US home, you will have 220 volt, 100 or 200 amp service.

In a typical home there are 4 separate connections. They consist of 2 "hot" wires, a ground, and a neutral.

We have what is called split-phase electric power. A distribution transformer has a single-phase input (primary) winding. The output (secondary) winding is center-tapped and the center tap connected to a grounded neutral. The other two wires are the "hot" wires, and have a voltage between them of about 220 volts. The voltage between each of them and neutral is half of that. That is why our system is often referred to as a 110 volt system.

The ground and neutral share a wire from the electric company. The neutral/ground wire gets attached to Earth Ground at the main breaker box, or at the meter (sometimes both). The Earth Ground is usually both a metal stake in the ground, and the building's water line (if it is metal).

The main breaker panel is the only one where the ground and neutral buses are attached to each-other. Even though the neutral and ground wires are connected to each other in the main panel, there may be a significant voltage between them near the end of a run.

There is never any loops in a properly wired building, with the possible exception of the ground wires.

For most lighting, and electrical outlets, you use one of the "hot" wires, along with a "neutral" wire for power, along with a ground wire for safety.

The white neutral wire gets attached to the neutral bus, and the bare, or green ground wire gets attached to the ground bus.

The hot wire is generally black, but may be any color other than white, or green. If a white wire is used as a hot wire it must be wrapped with electrical tape of another color. Common examples of white wires being used as a hot wire include end-of-line light switches, and for devices which use 220 volts without a neutral wire.

For switched lighting, and outlets, you always switch the hot wire.

For a given run the hot and neutral wires are always the same gauge. The ground wire is never smaller than the hot and neutral wires, in romex cable.

Armored cable, and wires run through metal conduit can often be run without a separate ground wire. Instead you would use the armor, or the conduit as the ground connection.

For appliances which require 220 volts, you will use two breakers which have a connection between them which will cause both breakers to turn on and off together. Newer breakers appear to be a single double-wide breaker which works the same way. Because of the way most breaker panels are arranged, two breakers side by side will be on separate phases.

There exists different plugs for each voltage, and current loads.

The major exception is for 110 volts, at 15 and 20 amps. 20 amp receptacles have an extra slot on the hot connection, but are otherwise identical to 15 amp receptacles. You can plug any 15 amp plug into a regular 20 amp receptacle.

It is very rare to actually see a device which has a 20 amp plug on them. This is because you will often have 15 amp only receptacles on a 20 amp service.

Most devices have no fuses, or breakers of their own.

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I have a few corrections to this. 1) The neutral wire is sometimes allowed to be smaller on a multiwire circuit whose wires are on opposite legs in the panel, since current going in one hot is going out the other at the same time, the neutral sees much less current going through it. 2) The ground wire now has to be at least as large as the hot and neutral- it has to be able to carry enough current to trip the breaker before starting a fire if there's a short to ground. 3) The neutral is NEVER to be used as a ground wire. It defeats the whole purpose. – nstenz Aug 26 '10 at 5:07

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