AC Plugs, Adapters and USB Wall Chargers

Read the blade layout: the plug shape sets voltage and amps

In North America a plug's blade layout tells you what it is for. A 5-15 plug has two flat blades and a round ground pin and is the standard 15 amp, 125 V household plug. A 5-20 plug has one blade turned sideways and fits only a 20 amp receptacle, which in turn accepts 5-15 plugs. Locking plugs, such as L5-20 or L6-20, twist to lock and are made for specific voltages and amps, so they will not fit an ordinary outlet.

International plug adapters use letters. Type A is two flat pins and Type B adds a round ground pin, which match the North American 1-15 and 5-15 shapes. An adapter changes the plug shape only, not the voltage, so check that the device accepts the local voltage before using it abroad; a voltage converter or transformer is a separate product.

Replacement plugs, ratings and approvals

A straight blade plug you wire yourself replaces a damaged cord end. Use the amp and voltage that match the cord and the appliance, and a plug with a cord clamp that grips the jacket so the wires do not take the strain. On US plugs, the brass screw takes the hot wire, the silver screw takes the neutral and the green screw takes the ground. A cracked or hot plug should be replaced, not taped.

Approvals matter on anything that carries mains power. Look for a UL, CSA or ETL listing on plugs and adapters, or CE in Europe, and for USB wall chargers check the output in volts and amps or watts against what the device needs. A charger that supplies at least the required power is fine; a weaker one charges slowly. Do not use a plug rated below the amps your appliance draws.

Questions about AC Plugs, Adapters and USB Wall Chargers

Can a plug adapter change voltage?

No. An adapter only changes the plug shape so the pins fit the outlet. If your device is rated for the local voltage, as many chargers are for a wide range, an adapter is enough; otherwise you need a voltage converter or transformer rated for the device's wattage.

What is the difference between a 5-15 and a 5-20 plug?

Both are North American straight blade plugs. The 5-15 is rated 15 A at 125 V. The 5-20 is rated 20 A and has one blade turned sideways, so it fits only a 20 A receptacle, while a 20 A receptacle accepts both plug types.

Which wire goes to which screw on a plug?

On US plugs, the hot wire goes to the brass screw, the neutral to the silver screw and the ground to the green screw. Strip just enough insulation, twist the strands, wrap them clockwise around the screw and clamp the cord jacket in the strain relief.