Electrical
Electrical
The Electrical domain tests safe diagnosis and installation of line-voltage and control circuits: Ohm’s law, motor circuits, capacitors, contactors, disconnects, grounding, and conductor sizing.
Core rules
- Ohm’s law: E = I × R; power: P = E × I. In series, current is common and voltage drops add; in parallel, voltage is common and currents add.
- Size conductors to the nameplate minimum circuit ampacity (MCA), not to the breaker. The overcurrent device may be larger, up to the maximum fuse or HACR breaker marked on the nameplate.
- A disconnect must be within sight of and readily accessible from the equipment. Bond metallic refrigerant and gas lines; use GFCI protection where the code requires it.
- Discharge capacitors before testing. Use a meter rated for the voltage and CAT rating.
Worked example
A condenser nameplate reads MCA 18 A and maximum fuse 30 A. A 12 AWG copper conductor at 60°C has 20 A ampacity, so it satisfies the 18 A MCA. The protection must not exceed 30 A. Sizing the wire to the 30 A breaker would be wrong; sizing the breaker to the wire alone would nuisance-trip.
Traps
Using locked-rotor amps for wire sizing; measuring voltage with the meter in series; leaving a capacitor charged; and assuming a 24 V control circuit is harmless if the transformer is miswired.