Electrical Trade Competency
What the exam tests
The electrical portion tests safe electrical work on HVAC/R equipment: Ohm's law and power, series/parallel circuits, motors and capacitors, contactors and relays, transformers and 24-volt control circuits, overcurrent protection, disconnects, grounding and bonding, conductor sizing, and the NEC requirements that apply to HVAC equipment.
Core rules and concepts
- Ohm's law: E = I × R. Power: P = E × I. In a series circuit current is the same; in parallel branches voltage is the same. Resistance readings must be taken with the component isolated and discharged.
- HVAC nameplate values govern branch-circuit and overcurrent selection. Use the minimum circuit ampacity for conductors and the maximum fuse/breaker marked on the nameplate; do not substitute a larger breaker because the unit keeps tripping.
- Article 440 of the NEC covers air-conditioning and refrigeration equipment. A disconnecting means must be within sight and readily accessible; grounding and bonding are safety systems, not optional.
- Capacitors store charge. Discharge and verify before touching. Start components, run capacitors, and potential relays must match the motor and wiring diagram.
- Control transformers step line voltage down to 24 V. A shorted or overloaded secondary can open the transformer fuse; never bypass it.
- Lockout/tagout and meter category ratings matter. Use the correct function and range; verify the meter on a known source.
Worked example
A single-phase compressor is rated 240 V and its winding measures 12 Ω. I = E/R = 240/12 = 20 A, and apparent power is 240 × 20 = 4,800 VA. If the nameplate says maximum 25 A, a 20 A reading is plausible; if the measured current is 30 A, check voltage, capacitor, and mechanical load before replacing the compressor.
Traps
Using a voltmeter in series; assuming a capacitor is bad because it looks swollen; ignoring nameplate MCA/MOP; wiring a contactor line/load backward; and treating a control-circuit fuse as a nuisance to upsize.