Real cases

Two of the ideas you practise, meeting in one real situation. Choose, see what actually happens, then reflect.

A case · you decide

Ohm & The Breaker — a 17-year-old electrical apprentice on her first service call

The idea in play: power = volts × amps, so current = watts ÷ volts; a breaker protects the wire, so you never fix a trip by fitting a bigger breaker.

A customer's garage breaker keeps tripping. On one 15 A circuit wired with 14-gauge copper, there is an 1,800 W heater and a 600 W kettle.

Ohm: power is volts × amps, so current = watts ÷ volts. 1,800 W + 600 W is 2,400 W; at 120 V that is 20 A. The heater alone is 15 A.

The Breaker: 14-gauge copper is protected at 15 A. The breaker trips to stop that wire from overheating.

What should the apprentice recommend?

Work the trade maths →

A case · you decide

The 80% Rule & The Breaker — a 16-year-old apprentice helping plan a car-charger install

The idea in play: a load that runs three hours or more may use only 80% of the breaker rating.

A customer wants to charge an electric car overnight on an existing 20 A, 120 V circuit. The charger can be set to draw 16 A or 20 A.

The 80% Rule: a continuous load (three hours or more) on a 20 A breaker may use only 16 A.

The Breaker still protects the wire. Running it at its limit all night is exactly what the rule prevents.

Which setting should they use?

Work the trade maths →