Structures Supplied by Other Than a Service, Part 5

If you use a branch or feeder from one building to supply power to another building, you generally can run only one branch or feeder for that purpose [225.30]. There are five conditions under which you can exceed this limit [225.30(A) - (E)]. The fourth one is "different characteristics."

What characteristics qualify?

The first three the NEC lists shouldn't confuse anybody:

1. Different voltages. Example: a shredder building for which the lights and receptacles operate on 120V brought over with a branch circuit, but you need 480V to operate the shredder motors.
2. Different frequencies. Example: a 50-Hz load that, obviously, you can't power from the 60-Hz feeder.
3. Different phases. Example: a building with 120V loads. To prevent phase imbalances, you supply that building with three feeders — each on a different phase.

Then the NEC lists a fourth: different uses. The NEC gives an example of controlling outside lighting from multiple locations [225.30(D)], but the vagueness here can put us on the slippery slope of ignoring the restriction altogether.

Suppose a building has a lighting circuit and three convenience receptacle circuits. Are those "different uses" or is this entire load, typically needed so a building can be occupied, a single use? If you're considering "different uses," discuss the situation with your local AHJ early in the project.