AC Power Extension Cords

Plug and outlet shapes: 5-15, 5-20 and locking types

In North America the common household plug is NEMA 5-15: two parallel blades and a round ground pin, rated 15 A. The 5-20 is the 20 A version, recognized by one blade turned sideways into a T. A 5-20 outlet accepts both plugs, but a 5-20 plug will not fit a 5-15 outlet. Locking types such as L5-20 twist to lock and only mate with their own kind, so they turn up in racks and workshops. An extension has a male plug at the supply end and a female outlet at the load end.

Reading gauge, amp rating and jacket letters on the cord

Thicker wire carries more current: 16 AWG suits lamps, chargers and electronics at roughly 13 A, 14 AWG handles about 15 A, and 12 AWG is for power tools and heavy loads, especially on longer cords. Match the cord to the appliance and keep long runs on the thicker gauge, because thin wire warms up under load. Jacket letters matter too: SJT is for indoor use, and a W in the code, as in SJTW, marks a cord rated for outdoor use. Never run a cord under a rug, and do not chain extensions.

Questions about AC Power Extension Cords

Is a 16 AWG extension cord enough for a PC and monitor?

Usually yes. A desktop PC with a monitor draws a few amps, well inside the roughly 13 A a 16 AWG cord can carry. Space heaters and other high-wattage appliances need a heavier cord or a direct wall outlet.

What is the difference between NEMA 5-15 and 5-20?

Both are grounded plugs, but 5-15 is rated 15 A and 5-20 is rated 20 A. A 5-20 plug has one blade turned sideways, so it only fits a 5-20 outlet, while a 5-15 plug fits either kind.

Can I use an indoor extension cord outside?

Not unless the jacket is rated for it. Look for an outdoor marking such as the W in SJTW, because indoor-only insulation breaks down in sunlight and damp, and the plug connection must be kept dry too.