Torque1st
MEMBER EMERITUS
Just one reason I keep all my old copies of the code. Old copies can sometimes be picked up at public library book sales.
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stupid sub panel question?
- Thread starter rust bucket bronco
- Start date
sparky1562
Well-known member
Copied from Bob Keis at code forum.
The panels in separate buildings are not really subpanels as far as code is concerned. They are the service equipment for the structure. You can have a subpanel from the service equipment in each building if you want. Between buildings, section 250.32 applies and if there are metal interconnections between buildings such as water piping, or air lines, or any metal interconnection at all, then you must install an equipment ground wire so if you have a 120/240 system, you would have four wires. The neutral would be separated in each building and a grounding bar would be installed, just like a subpanel. Then the code requires a grounding electrode conductor (GEC) to a grounding electrode (usually a ground rod). The GEC will be connected to the equipment ground bar at each building. This is not to clear overcurrent devices, this is for two reasons. One is lightning, the more important one is to put the equipment ground at the same relative potential as the earth. This is for step potential or touch potential voltages so that what you touch in the building is at the same potential as what you are standing on. Now the tricky part. If you do not have any interconnecting metal between buildings, the code allows you to install three conductors between buildings. When you do this you bond the neutral and ground the neutral just like a new service. Some inspectors think that every panel in a separate building must be treated as a subpanel, but this is not true. In past codes (1996 and older) these rule were in section 250-24 and Exception 2 addressed the grounding bus.
This has been changed in the 2008 code. Now you have to pull the ground wire, not an option. That part about metal to metal connection always confused people. What about a pone line or Cable TV? I might go out on the NFPA web site and see why they changed it.
On edit: here are the comments, page 70-193
http://www.nfpa.org/assets/files/PDF/ROP/NEC2008Article250-280.pdf
Last edited:
sberry
Banned
I believe it includes phones or cable, says ANY metal. I agree, in todays world it only makes sense to use 4 wire.