General Electrical Knowledge, Theory, and Code Administration
What this domain covers
Domain 1 pairs fundamental theory with the NEC's administrative articles (90, 100, 110) and Washington's electrical law: RCW 19.28 and WAC 296-46B, administered by the Department of Labor & Industries. Expect calculation items (Ohm's law, power, series/parallel, voltage drop) mixed with "who may do what" items - licensing, permits, inspections, variances, and the authority of the AHJ.
Theory to have cold
- V = I x R; P = V x I = I squared x R = V squared / R.
- Series: current is common, resistances and voltage drops add. Parallel: voltage is common, branch currents add, and total resistance is always less than the smallest branch.
- A continuous load runs three hours or more; where the Code requires it, size conductors and overcurrent devices at 125% of the continuous load plus 100% of the noncontinuous load.
- Working clearances in 110.26 are measured from live parts, not from the enclosure door or dead front.
Traps the exam likes
- The 110.26(A)(1) depth table is keyed to voltage to ground, not phase-to-phase. A 480Y/277 V panelboard uses the 151-302 V row.
- Condition 2 and Condition 3 add depth (exposed live parts on both sides, or grounded surfaces opposite live parts).
- Questions on licensing assume the NEC applies as amended by Washington rule; local jurisdictions may amend further, so the AHJ governs.
Worked example
A 480Y/277 V panelboard has exposed live parts on one side and a grounded wall opposite (Condition 2). Voltage to ground is 277 V, so the 151-302 V row applies: 3.5 ft in Condition 1, 4 ft in Condition 2, 5 ft in Condition 3. Answer: 4 ft of depth, 30 in wide (or the width of the equipment if wider), and 6 ft 6 in of headroom.
Rule of thumb: clearance depth follows the voltage to ground, width follows 30 in, height follows 6 ft 6 in, and that space stays clear of storage.