How it works & the NEC rules behind it
Conduit bodies (LB, LL, LR, T, C fittings) provide access to raceways for pulling conductors. Under NEC §314.16(C) and §314.28, sizing rules split sharply based on conductor gauge:
Two Distinct Code Regimes:
- 1. Conductors Smaller Than #4 AWG (§314.16(C)(1)): Sized by cubic-inch volume. The total volume of all enclosed conductors (based on Table 314.16(B) volume allowances) must not exceed the marked cubic inch capacity on the fitting. Furthermore, the number of conductors cannot exceed the standard Chapter 9 conduit fill limit.
- 2. Conductors #4 AWG and Larger (§314.28): Must satisfy physical dimension rules to prevent damaging wire insulation during sharp pulls:
- Angle Pulls (LB, LL, LR fittings, §314.28(A)(2)): The distance from where conduit enters to the opposite wall must be at least 6 times the conduit trade size.
- Straight Pulls (C fittings, §314.28(A)(1)): Distance between conduit entries must be at least 8 times the conduit trade size.
- 3. Mogul Conduit Bodies (§314.28(A)(3)): Standard compact LBs are typically NOT listed for 3 or 4 large feeder conductors (e.g. 500 kcmil). When pulling large feeder cables, an elongated Mogul Conduit Body or oversized junction box is legally required.