Case Study 13a Plug Picture

The UK mains electricity supply is about 230V and can kill if not used safely. Electrical circuits, cables, plugs and appliances are designed to reduce the chances of receiving an electric shock. The more electrical energy used, the greater the cost. Electrical supplies can be direct current (d.c.) or alternating current (a.c.).

Wiring a plug

You should know the features of a correctly wired three-pin mains electricity plug and be able to recognise errors in the wiring of a plug.

The cable

A mains electricity cable contains two or three inner wires. Each has a core of copper, because copper is a good conductor of electricity. The outer layers are flexible plastic, because plastic is a good electrical insulatorinsulator: Material that is a poor conductor of electricity or heat.. The inner wires are colour coded:

Colours of inner wires within a cable

green and yellow stripesearth

The plug

The features of a plug are:

  • The case is made from tough plastic or rubber, because these materials are good electrical insulators.
  • The three pins are made from brass, which is a good conductor of electricity.
  • There is a fusefuse: An electrical component that protects circuits and electrical devices from overload by melting when the current becomes too high. between the live terminal and the live pin.
  • The fuse breaks the circuit if too much current flows.
  • The cable is secured in the plug by a cable grip. This should grip the cable itself, and not the individual wires inside it.

The inside of a plug

The diagram shows the key features of a correctly wired three-pin mains plug.

Where does each wire go?

There is an easy way to remember where to connect each wire. Take the second letters of the words blue, brown and striped. This reminds you that when you look into a plug from above:

blue goes left, brown goes right and striped goes to the top.

Back to Electricity index

Wiring an American Plug is no more difficult than wiring a UK or European plug… but over here getting hold of them is much more difficult and they are quite expensive!

So much so, a full American cord set with moulded connectors as shown on our Mains Leads page will cost less than the rewireable plug… But if you want to buy American connectors then why not check out our NEMA5-15P plug or our NEMA5-15RX extension socket.

Alternatively if you can’t find what you’re looking for either take a look at our International Plugs and Sockets page or give us a call, you can find our details here.


Electricity can KILL!! If you are in any doubt at all about what you are doing, or your ability to do the work, you should refer any mains connection work to a qualified electrician.

NEMA 1-15

All NEMA 1 devices are two-wire non-grounding connectors rated for 125V maximum. NEMA 1-15P are the two-prong plugs commonly found on household lamps and consumer electronics such as clocks

and radios as well as on “double-insulated” small appliances. The corresponding sockets have not been allowed in new construction in the United States or Canada since about 1965, but remain in place in many older homes and are still sold “for replacement use only”.

Early examples were symmetrical, but later sockets and most newer plugs distinguish the neutral conductor by making it slightly wider than the hot one. Such newer plugs often will not fit in old sockets, but both versions fit in type B sockets. Some devices that meet strict standards, such as sealed electronic power supplies, are still sold with both pins narrow.The neutral insertion point in the modern type A socket is wider to accommodate polarized type A plugs.


NEMA 2-15

The NEMA 2-15 range of connectors have been effectively discontinued for some time.  However, if you find yourself faced with one of the these in a repair environment the wiring convention is the same as for the 1-15 range.

NEMA 5-15 / CS22.2, Nº42


The type B mains plug has two flat parallel pins with the same geometry as type A, and a rounded ground or earthing pin, commonly formed from flat metal folded into a ‘U’ shape but in some cases solid pins may be used. The connector is rated at 15 amps and 125 volts maximum. The American standard for this connector is known as NEMA 5-15, and the Canadian standard CSA 22.2, Nº42.

The American and Canadian connectors are effectively identical.The ground pin is longer than the two parallel pins so that the device is grounded before the supply is connected. The neutral insertion point in the type B socket is wider to accommodate polarized type A plugs, but the type B plugs often have both pins narrow, the ground pin enforcing polarity.

With American and Canadian plugs, if you look directly at a socket, the ground socket will be at a bottom, the live slot is on the right and the neutral slot is on the left. If the plug is polarized, the widest slot is the neutral connector.This view is the same as looking at the solder side or screw side of a rewireable plug, as shown in the diagram to the left.



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