Before installing the distribution system, calculate the loads per Sec. 551.73 of the National Electrical Code (NEC). The distribution system must be capable of supporting the recreational vehicle (RV) receptacles and site supply equipment per those calculations [Sec. 551.72(A)].
An RV park distribution system must have an ampacity of at least 30A. Permitted systems include:
- A single-phase system that’s 120V, 120/240V, or 120/208V [Sec. 551.72(A)].
- A three-phase system that’s 208Y/120V [Sec. 551.72(B)].
If the latter, the feeders must include one grounded conductor and one equipment grounding (bonding) conductor; the feeders are permitted to also have two ungrounded conductors. Distribute the loads as equally as practicable [Sec. 551.72(B)].
Receptacles rated at 50A must be supplied from a branch circuit that has the same voltage class and rating as the receptacle [Sec. 551.72(C)].
You can reduce the size of neutral conductors below the minimum required size of the ungrounded conductors, but only for 240V, line-to-line permanently connected loads [Sec. 551.72(D)]. However, the small cost-savings is probably not worth the performance hit.
RV parks typically have long circuit lengths, so upsizing the conductors to reduce voltage drop is strongly advised [Informational Notes following Sec. 551.72].