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Structures Supplied by Other Than a Service, Part 6

Documented safe switching procedures for structures supplied by other than a service

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 fifth one is "documented safe switching procedures." Unfortunately, the NEC doesn't define or explain what these are. This last exception comes after a list of four specific reasons for an exception, making it act as an "other" option on a multiple choice quiz.

If you have some reason other than the other four listed in 225.30(A) - (D), you can exceed the single feeder or branch circuit limit if your facility establishes and maintains these procedures. But still, this leaves a large area of the unknown. How do you resolve that?

A key phrase repeated throughout the NEC is "acceptable to the authority having jurisdiction." Approval lies ultimately with the AHJ. So how do you know what the AHJ would consider acceptable? Look again at that requirement. What word jumps out? Hint: It's the underlying principle of 90.1(A), which states the purpose of the NEC.

Before you approach the AHJ for approval, analyze the potential risks and design your procedures to minimize or eliminate them. And ensure that qualified individuals will monitor the installation [225.32, Exception 1].

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