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Breaker and wire size calculator (Philippines)

The breaker and the mm² THHN or PDX for an appliance or a circuit, by the Philippine Electrical Code.

Try the circuit in the labBuild it on the simulator's bench and measure it.

How it is worked out

Two rules from the Philippine Electrical Code (which follows the NEC): a motor load or a continuous load (anything on for three hours or more, a water heater, lights, an aircon) is sized at 125 % of its running current, and the cable must be rated for the breaker, because the breaker protects the cable, not the appliance.

Example: a 1.5 HP aircon at 230 V draws about 6 A running; 125 % is 7.5 A, so a 15 A or 20 A breaker on 3.5 mm² THHN, on its own circuit. A 3.5 kW water heater draws 15.2 A; 125 % is 19 A, so a 20 A breaker is at its limit and a 30 A breaker on 5.5 mm² is the usual choice.

The horsepower conversion assumes 80 % for efficiency × power factor, which fits window aircons and small pumps; use the nameplate amps when you have them. Then check the run: a long run to a shed or a water pump needs a bigger size for voltage drop than for current.

Build the circuit and overload it: the aircon circuit, the water heater circuit and the house wiring simulator.

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