Are Grounding Bushings Required?

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joemiki

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I need a clarification.

I'm feeding a 30kva transformer from a 277/480 volt panel. then the transformer will feed a 120/208 panel.
This system is piped together using EMT, changeover and Flex Metal conduit on both sides (Primary/Secondary).

I've always been under the impression that on the secondary side of the transformer (120/208 volt), before the overcurrent protection. I was required to use BONDING/GROUNDING BUSHINGS and run my grounded conductor through them. This 120/208 would be a New Service from a separately derived system.

Thank You, Joe Miki
 
joemiki said:
I've always been under the impression that on the secondary side of the transformer (120/208 volt), before the overcurrent protection. I was required to use BONDING/GROUNDING BUSHINGS and run my grounded conductor through them.
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If your system bonding jumper is not in the transformer (which is the common method around here), then the grounded conductor would perform the bonding to the first means of disconnect.

250.118(5) states that unless you installed a 20A OCPD somewhere in there ( ;) ) that the FMC is not an acceptable EGC - but for it's own sake, it's considered bonded where listed fittings are used (as required by 348.6).

I do not see any requirement for using bonding bushings around transformers, so IMO the normal rules would apply (250.96, .97). However, this is a common practice from what I've seen, so I could be wrong.

This 120/208 would be a New Service from a separately derived system.
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No, it is not a service. It is a seperately derived system. See the definitions in Article 100. :)

Welcome to the forum. :)
 
For the installation described in the OP bonding bushings are not required. As George said this is an SDS not a service so the service raceway bonding requirements do not apply. I've seen many a bonding bushing on transformers, but if your using FMC they're serving no real purpose and are not required.
 
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