Electrical Trade Knowledge (Master Electrician)
Beyond the journeyman scope
The master exam assumes journeyman fundamentals and adds design responsibility: service and feeder calculations, load diversity, short-circuit current and interrupting ratings, selective coordination, transformer connections, and plan interpretation. Expect calculation-heavy items and questions about supervising work and interpreting code intent.
Concepts to master
- Service/feeder calculations: standard method vs. optional method; demand factors for dwellings; adding largest motor at 125%.
- Available fault current and AIC: equipment interrupting/withstand ratings must meet or exceed available fault current; series-rated systems require listed combinations.
- Coordination: overcurrent devices arranged so the device nearest the fault opens first.
- Transformers: turns ratio, primary vs. secondary current, wye vs. delta, grounding of separately derived systems.
- Power factor and correction: kVAR = P × (tan θ1 − tan θ2).
Traps to expect
Candidates lose points by applying the optional method when the question implies the standard method, forgetting the 125% largest-motor adder, or confusing kVA with kW when power factor is not unity. Neutral sizing questions hinge on whether the load is nonlinear (triplen harmonics). Also watch for "minimum" service size versus "calculated load" - they are not the same number.
Worked example
A dwelling has a calculated general load of 12,000 VA plus a 7,200 VA range at demand factor 0.8 and a 4,500 VA water heater at 100%. Total = 12,000 + 5,760 + 4,500 = 22,260 VA. Add the largest motor at 25% if applicable. Service at 240 V: 22,260 / 240 ≈ 92.8 A, so a 100 A service is the minimum standard size that covers the load. Confirm against the applicable article before finalizing.
Rule of thumb
When power factor is given, always convert kW to kVA (kVA = kW / PF) before sizing conductors or transformers.