Practical Safeguarding of Persons and Property from Electrical Hazards
Grounding, bonding, and fault clearing
Bond metal enclosures, raceways, and equipment to the equipment grounding conductor so fault current returns to the source and opens the overcurrent device. Bond the service neutral at the service only; in subpanels, keep neutrals and equipment grounds on separate bars. Do not create objectionable current on grounding paths.
Overcurrent and conductor protection
The overcurrent device must protect conductors at their ampacity, with the small-conductor rules and motor-circuit allowances applied correctly. Use terminals and conductors within their temperature and ampacity ratings; “it works” is not a Code basis.
GFCI and AFCI
GFCI protection reduces shock risk by sensing imbalance; it is required in bathrooms, kitchens, outdoors, garages, unfinished basements, and other listed locations. AFCI protection reduces fire risk from arc faults on dwelling-unit branch circuits. GFCI does not substitute for an equipment grounding conductor.
Working space and box fill
Provide 110.26 working clearance: at least 36 in deep, 30 in wide, and 6.5 ft high. For box fill, count each conductor, the equipment grounding conductor, clamps, and devices using Table 314.16(B) volume allowances.
Worked example
A 4 in × 4 in × 1.5 in metal box has 21 cu in. It contains two 12 AWG circuit conductors, one 12 AWG EGC, one cable clamp, and one receptacle. At 2.25 cu in per 12 AWG: two conductors = 4.50; EGC = 2.25; clamp = 2.25; receptacle = two conductor equivalents = 4.50. Total = 13.50 cu in, so the 21 cu in box is adequate.
Traps
- Bonding neutral and ground together in a subpanel.
- Treating GFCI as a replacement for grounding.
- Missing AFCI/GFCI locations or using the wrong device type.
- Measuring working space from the wrong face or ignoring width/height.
- Miscounting box fill: forgetting EGC, clamps, or devices.