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WA Electrician: Wiring Methods, Materials, and Installation Requirements

WA Electrician · Work through your exam, one topic at a time.

All guide sections

Wiring Methods, Materials, and Installation Requirements

Scope

This domain covers the general rules of Article 300, conductors (Article 310), boxes and fill (Article 314), the raceway and cable articles (320-362), bonding and grounding (Article 250), and the outlet requirements of Article 210, including GFCI (210.8), AFCI (210.12), and receptacle spacing (210.52).

Numbers worth memorizing

  • Conduit fill, Chapter 9 Table 1: 53% for one conductor, 31% for two, 40% for over two. A nipple 24 in or less may be filled to 60%.
  • Box fill, Table 314.16(B): 14 AWG = 2.0 cu in, 12 AWG = 2.25, 10 AWG = 2.50 per conductor. All equipment grounding conductors together count as one conductor of the largest size; each cable clamp counts as one; device yokes count per 314.16(B)(4).
  • Securing and supporting: NM cable within 12 in of a box and at intervals not over 4.5 ft (334.30); EMT within 3 ft of a box and at intervals not over 10 ft (358.30); rigid nonmetallic conduit per Table 352.30 (typically 3 ft for smaller trade sizes).
  • 300.14 requires at least 6 in of free conductor at each box, extending 3 in beyond the box face.

Traps

The classic errors are confusing the 40% fill rule with the 60% nipple allowance, mixing "secured" with "supported," using NM cable where it is prohibited (wet locations, most masonry voids, exposed in some occupancies), and forgetting that conductor ampacity must be corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway.

Worked example

Receptacle spacing in a dwelling: 210.52(A)(1) requires that no point along the floor line of any wall space be more than 6 ft from a receptacle outlet. That yields a maximum of 12 ft between receptacles, and any wall space 2 ft or wider needs its own outlet. For a 20 ft wall starting at a door, place outlets so the first is within 6 ft of the corner - 6 ft from each end of the measured run works.

Rule of thumb: measure wall space along the floor line, break it at doorways and fixed barriers, and treat any 2 ft or wider segment as requiring an outlet.