Bonding old service 4-400A switches

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jibron

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Location
Ohio
AHJ wants old service brought up to code after fire. Won't allow power back on till grounding is right.
I have 4 - 400A, 480VAC switches being fed from a transformer just outside the wall. All taps are outdoors.
Rather than taking everything apart to install grounding lugs, I was going to use large Burndy pipe clamps on the line side 3" rigid conduits with a 2/0 woven through them and cadwelded to building steel. The clamps are listed for rigid conduit.
At the incoming water I will also clamp and cadweld a conductor to building steel.
Off the conduit 2/0, I was going to irreversible "C" tap conductors to a through bolted lug to each switch and bolt to cleaned steel to bond the switches.
Am I missing something or is this a plan?

Thanks
 
augie47

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I believe you are missing a few things.
First, the pipe clamp plan should work for bonding the service conduits but if you weave the GEC thru all the clamps, a 2/0 will not be large enough (assuming 500 kcmil service conductors). If you "hit" all 4 with one wire you will need to size per 250.102(C) and I think the math will require a 250 kcmil. You can bond to each clamp individually per 250,66, most likely a 1/0
Secondly, the NEC requires the GEC connect to the grounded conductor (assuming you have one), so bonding to the enclosure will not satisfy 250.24(A)(1). The connection should be made to the grounded conductor, then bonded to the can (if there is no bonding jumper present now) then to water & building steel. If you are connecting to the water or steel with one conductir for all four service disconencts, it would need to be a 3/0.
If there is no grounded conductor your plan for connecting to the enclosure should work.
 
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