Q
What is the intent of the NEC Section 225-32 Exception 1 when it says that a disconnect can be located elsewhere where safe switching procedures are documented? Is it the same as Section 225-30(e)? We were designing feeders for a complex of four buildings under “one management.” As we understand it, each building can only have one feeder with a disconnect on the outside or just inside the building. The Code handbook makes a comment that there can be more than one feeder to a building where there are secondary loop supply networks, and key interlock systems to serve as the documented switching procedures.
My question is, does another way exist to feed a remote building under one management with more that one feeder — and if so, how can you meet the requirement for safe switching procedures? Let's say that we have a building with three panelboards. Can we just bring three feeders to the building from the “main” building and somehow document the switching procedures to disconnect the remote building?
A
Both Section 225-32, Exception No. 1 and Section 225-30(e) are referring to the same issue. However, 225-32 is about locations of disconnects and 225-30 is about numbers of supplies. The general rule is that there should be only one feed to a building and the disconnect should be located either outside or inside nearest the point of entrance. Where there are “documented safe switching procedures,” more than one feed may be permitted and/or the disconnecting means may be remotely located. If you have documented safe switching procedures, you are permitted by the Code to have more than one supply. The location of the disconnect may either follow the usual requirement, or the same switching procedures may permit the disconnects to be remotely located. You can also locate the disconnect remotely even though you have only one feed. With acceptable procedures you may use either rule or both.
The NEC does not define what a safe switching procedure should be. The NEC Handbook offers only one example. Many multibuilding sites are treated by maintenance crews pretty much the same as if they had one large building with multiple rooms. Key interlock systems are not necessarily a requirement. If the main switchroom is always supervised, for example, and everyone knows how to contact the person controlling that room, a system of posted notices along with a defined procedure may well be sufficient.
Remote controls such as those that might be provided by shunt-trip breakers is another possible method. The whole idea is that disconnection of a building from its source(s) of supply must be easily accomplished when there is a need.
The final determination of what procedures are acceptable is between you and the AHJ who may want to consider the type of facility, the nature of the risk, the degree of public access, the supervision of the system and other issues.
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Dann Strube, a nationally recognized NE Code expert, is a certified NE Code inspector in Indiana. He also teaches NE Code workshops.
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Noel Williams has taught the NFPA's NE Code Seminars for 10 years and is co-author of the NFPA's 1999 NE Code Changes. He's a licensed electrical inspector.