Structures Supplied by Other Than a Service, Part 7

How many disconnects can you have if you use a branch or feeder from one building to supply power to another?

If you use a branch or feeder from one building to supply power to another, how many disconnects can you have? The answer is six per each supply [225.33(A)] that's permitted by 225.30. This six disconnect rule is consistent with the six disconnect rule for services [230.71]. But don't install six disconnects just because the NEC permits that many. If you can design your system with fewer disconnects, that’s even better.

From a physics standpoint, you could have 20 disconnects and your system would function just fine. So why would two disconnects be better than six (if this is practical for your system)?

As you add disconnects, it takes longer for first responders to open them all. Where practical, "less is more" when it comes to supply disconnects.

This same concern for reducing time lost in an emergency response is why the disconnects must be grouped [225.34(A)]. There is a notable exception to this grouping rule. Obviously, the first responders aren't going to shut off your fire pump. The exception in [225.34(A)] permits you to locate the fire pump disconnect remote from the others. This exception can probably be deleted from a future revision, because in [225.34(B)] the NEC requires you to locate this disconnect remotely. It also extends that requirement to emergency, legally required, and optional standby systems.

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