Structures Supplied by Other Than a Service, Part 3

"Special occupancies" allows you to exceed the limit of one branch or feeder to supply power from one building to another building [225.30(A) - (E)]. 

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 second one is "special occupancies."

Not coincidentally, the title of Chapter 5 is "Special Occupancies." These include hazardous (as defined by OSHA and based on the type of combustibles present in sufficient quantity to cause ignition) locations (500 – 510), places with fuel and solvents (511 – 516), places that contain many people (517 – 540), prefab and sheet metal buildings (545 – 552), locations where there's water (553 and 555), and temporary installations.

For these types of occupancies, you can get special permission to exceed the limit. The phrase "special permission" has a specific meaning, as defined in Art. 100 of the NEC. It's the "written consent of the authority having jurisdiction."

This consent does not, for reasons including potential litigation, come easily. And you can get it only if you have one of two situations:

  1. It's a multiple-occupancy structure where there's no space available for supply equipment to all occupants.
  2. It's a single structure occupancy that's so large it needs an additional service.

In either case, consult the architect before seeking this consent.

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