WA Electrician cheat sheet

Ohm's law: E = I × R; power: P = E × I = I²R = E²/R, where E is volts, I is amperes, R is ohms, and P is watts.

Single-phase voltage drop: VD = (2 × K × I × L) ÷ CM, where K = 12.9 for copper and 21.2 for aluminum; a three-phase circuit substitutes 1.732 for the 2.

Series circuit: current is common, voltages add, resistances add. Parallel circuit: voltage is common, currents add, and total resistance is smaller than the smallest branch.

Continuous loads, defined as operating three hours or more, require conductors, overcurrent devices, and feeders sized at 125 percent of the load (210.19, 210.20, 215.2).

Washington adopts the NEC through WAC 296-46B; the Department of Labor & Industries administers electrical licensing, permits, and inspections statewide.

Dwelling general lighting load is 3 VA per square foot (220.12); each small-appliance and laundry branch circuit is computed at 1,500 VA.

Lighting demand factors (220.42): first 3,000 VA at 100 percent, 3,001 through 120,000 VA at 35 percent, and the remainder at 25 percent.

Conductor ampacity comes from Table 310.16 and is limited by termination ratings per 110.14(C); 14, 12, and 10 AWG are held to the 60°C column unless the equipment is marked otherwise.

A permit must be obtained from the authority having jurisdiction before electrical work begins, and the installer must request inspection before the work is concealed.

Type NM cable is limited to the 60°C ampacity column (334.80), is permitted only in dry locations, and must be secured within 12 inches of boxes and at intervals not exceeding 4.5 feet.

Support spacing: EMT and rigid metal conduit within 3 feet of a box and every 10 feet; PVC Schedule 40 every 3 feet.

Raceway fill (Chapter 9, Table 1): one conductor 53 percent, two conductors 31 percent, three or more conductors 40 percent of the interior cross section.

Box fill counting (314.16): one volume allowance per conductor entering the box, one for each yoke or strap, and one for all equipment grounding conductors combined.

Working space at equipment (110.26): at least 3 feet deep for 0-150 volts to ground, 30 inches wide, 6 feet 6 inches high, and kept clear of storage.

Ampacity adjustment for current-carrying conductors in a raceway (310.15(C)(1)): 4-6 conductors 80 percent, 7-9 conductors 70 percent, 10-20 conductors 50 percent.

Cable through bored holes less than 1¼ inches from the nearest edge of a stud or joist requires a steel plate at least 1/16 inch thick (300.4(A)).

Identification: the grounded conductor is white or gray, the equipment grounding conductor is green, green with yellow stripes, or bare (200.6, 250.119).

Metal raceways and enclosures must be bonded to the equipment grounding conductor, and an expansion fitting is required where PVC crosses a building expansion joint (352.44).

Dwelling receptacle spacing (210.52(A)): no point along the floor line may be more than 6 feet from a receptacle, and any wall space 2 feet or wider needs one.

Kitchen countertop receptacles (210.52(C)): no point along the counter wall may be more than 24 inches from a receptacle, with at least one per island or peninsula.

GFCI protection is required for 125-volt, 15- and 20-ampere receptacles in bathrooms, garages, outdoors, kitchens, laundry areas, and unfinished basements (210.8(A)).

Motor short-circuit protection (430.52): inverse-time breaker up to 250 percent, dual-element time-delay fuse up to 175 percent, non-time-delay fuse up to 300 percent of full-load current.

Motor branch-circuit conductors must have an ampacity of at least 125 percent of the full-load current from Tables 430.248 through 430.250 (430.22).

Motor overload protection (430.32): 125 percent of nameplate full-load amperes where the service factor is 1.15 or greater, 115 percent where it is less.

A motor disconnecting means must be within sight and within 50 feet of the motor and driven machinery unless it is capable of being locked open (430.102).

Panelboards require overcurrent protection on the supply side (408.36), and service disconnecting means may consist of no more than six switches or breakers in a single enclosure.

Luminaires weighing up to 50 pounds may be supported by a listed outlet box; heavier luminaires require independent support (314.27, 410.36).

Pool receptacles (680.22): at least 6 feet from the inside wall of the pool and not more than 20 feet from it.

Overhead conductors near pools (680.8): insulated conductors up to 750 volts require 10 feet of horizontal clearance from the pool edge, with greater distances where diving structures exist.

PV rapid shutdown (690.12): conductors more than 1 foot from the array must be reduced to 80 volts or less within 30 seconds.

Class I Division 2 covers locations where ignitable gas or vapor concentrations occur only under abnormal conditions; Division 1 covers normal operating conditions (Article 500).

Emergency systems (Article 700) must supply exit and emergency lighting for at least 90 minutes.

Temporary wiring on construction sites (590.6): all 125-volt, 15- and 20-ampere receptacles require GFCI protection.

In commercial repair garages, the space up to 18 inches above the floor is a classified location because heavier-than-air flammable vapors settle there (Article 511).

NFPA 70E establishes limited, restricted, and prohibited shock approach boundaries plus an arc flash boundary at an incident energy of 1.2 cal/cm².

Health care facilities (Article 517) use an essential electrical system split into critical and equipment branches; patient care area receptacles require hospital-grade bonding.