Electrical Contracting Practice and Theory
This domain tests the calculations and business judgment a journeyman needs before a wrench is picked up: circuit and feeder loading, conductor and raceway sizing, motor math, and the paperwork that turns a job into a legal, profitable project. Expect stand-alone calculation items and scenario items about bidding, permits, and change orders.
Theory that the exam reuses
- Ohm's law and power relationships, series/parallel resistance, single-phase versus three-phase voltage and current relations (line versus phase), transformer turns ratios, power factor, and why AC impedance - not DC resistance alone - governs voltage drop.
- Continuous versus noncontinuous loads: 210.19(A) and 210.20 require 125% of the continuous load plus 100% of the noncontinuous load for conductors and overcurrent devices.
- Motor branch circuits and feeders (Article 430): branch conductors at 125% of Table 430.250 full-load current, feeders at 125% of the largest motor plus the sum of the others.
- Voltage drop is an informational recommendation (roughly 3% branch, 5% total), not a mandatory rule - but plans and specs often make it contractual.
Worked example: dwelling general lighting, standard method
A 2,400 sq ft single-family dwelling, no special loads. General lighting = 2,400 × 3 VA = 7,200 VA. Add two 1,500 VA small-appliance circuits (3,000 VA) and one 1,500 VA laundry circuit. Total = 7,200 + 3,000 + 1,500 = 11,700 VA. Apply the 220.42 demand schedule: first 3,000 VA at 100% = 3,000; remaining 8,700 VA at 35% = 3,045. Demand load = 6,045 VA. At 240 V single-phase that is about 25 A of service capacity before fixed appliances, ranges, dryers, or heating are added - those go in separately with their own demand factors.
Traps that cost marks
- Charging 100% of general lighting instead of applying the 220.42 tiers.
- Forgetting that small-appliance and laundry circuits are 1,500 VA each and are added before the demand factors.
- Mixing volt-amperes with amperes, or applying the 35% step to the first 3,000 VA.
- Adding noncoincident loads (220.60) at full value instead of using the larger of the two.
- Treating a 3% voltage drop as a code violation rather than a design target.