Lesson 2
Watts, Amps and Why Wires Melt
Turn watts into amps, see why the heat in a wire grows with the square of the current, and know what a lead, a reel and a fuse can take.
A heater on a reel
It’s a cold January evening, the spare room has no socket near the bed, and someone runs a 2 kW fan heater off an extension reel. It feels ordinary. This lesson is about why it isn’t: Electrical Safety First advises against running portable heaters from extension leads at all.
Start with power, measured in watts (W): how fast energy is delivered. Power is voltage × current, so current = power ÷ voltage. A 2 kW heater on a 230 V supply draws about 2,000 ÷ 230 ≈ 8.7 amps. A 3 kW kettle draws about 13 amps, nearly everything a UK plug is built to carry.
That sum works well for things that simply heat, like kettles, heaters and irons. Motors and electronics can draw a little differently, so their rating plates have the final say.