Separate Building or Not

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Sparky2791

Sparky2791

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Northeast, PA
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Electrical Design
Scenario:

Existing building has a 1200A 120/208V 3 phase service. The GES is already established at the existing building.

New addition will have a new stair tower that attaches to the existing building making it all one building. The existing building steel will not attach to the new building steel.

The new addition will be fed with a 400A feeder via a 400A breaker in the existing 1200A service distribution panel.

Question:

Since existing and new building steel are not mechanically connected, does the building steel for the new addition need a bonding jumper from the existing building steel otherwise the new addition would be considered a remote building and therefore 250.32 (B) would apply? Also, if it is considered a remote building the EGC would be sized on 250.122 not 250.66 in the 400A feeder according to that section.
 
I would bond the steel and treat it all as one building. Even if you don't intentionally bond the steel, I would imagine you will end up with conductive paths between the addition and the existing building that will end up bonding it for you.
 
d0nut said:
I would bond the steel and treat it all as one building. Even if you don't intentionally bond the steel, I would imagine you will end up with conductive paths between the addition and the existing building that will end up bonding it for you.
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Exactly, I would just jumper steel to steel at a convenient and substantial point. One jumper say at substantial vertical supports so the I beams can be assumed to have pretty good Earth contact exposure (concrete encased steel going into the ground).

There is not a code requirement for that, that I am aware of. Building or Fire code could treat them as two different adjacent buildings. So if it's not specc'd or on the drawing I would probably treat it as a change. Present it and ask for permission, if the owner wants the extra work done.

The new feeder and subpanel has its own EGC. I don't see how a GEC GES tie would also be necessary per code. The remote building classification would be made by others. You could ask the AHJ if he would require it. With adjacent buildings and different owners common, this is something routinely found missing, an intended building steel to building steel jumper. I would not call the bonding jumper either a GEC or an EGC.
 
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