How it works & the NEC rules behind it
Properly securing and supporting electrical cables and raceways prevents mechanical strain on terminals, sagging, and physical damage. The National Electrical Code (NEC Chapter 3) specifies precise maximum distances for fasteners, straps, and hangers.
Support Rules by Wiring Method:
- NM-B (Romex, §334.30): Must be secured within 12 inches of every box/enclosure and at intervals not exceeding 4.5 feet (1.4 m).
- Type MC Cable (§330.30): Must be secured within 12 inches of every box/fitting and at intervals not exceeding 6.0 feet (1.8 m). Cables with 4 or fewer conductors (≤ #10 AWG) can be fished without strapping.
- EMT Conduit (§358.30): Must be fastened within 3 feet (900 mm) of every box, conduit body, or termination, and at intervals not exceeding 10 feet (3.0 m).
- RMC / IMC Steel Conduit (§344.30): Fastened within 3 ft of boxes. Where made up with threaded couplings, straight horizontal runs permit spans from 10 ft (1/2"–3/4") up to 20 ft (3"+) per Table 344.30(B)(2).
- PVC Conduit (§352.30): Fastened within 3 ft of boxes. Support spacing varies by trade size from 3 ft (1/2"–1") to 7 ft (4") per Table 352.30. Expansion fittings required where temperature variation exceeds 25°F.
- Flexible Metal Conduit (FMC, §348.30): Fastened within 12 inches of box and every 4.5 feet.