Bonding XFMR GEC to rebar for ungrounded system

D

Dale001289

Senior Member
Location
Georgia
We have a 2000kVA, 15kV-480V, 3ph, 3W, delta-delta ungrounded dry type transformer that ties into a 480V load break disconnect immediately adjacent to the XFMR.
The XFMR GEC comes up thru the concrete mounting pad into XFMR housing. The pad has lots of rebar. So should the rebar be bonded to the XFMR GEC since the switch represents the service entrance? Or does it even matter since the system is ungrounded to begin with?
 
don_resqcapt19 said:
The only difference between the bonding and grounding requirements for grounded and ungrounded systems is that the ungrounded system does not have a main bonding jumper.
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Thanks Don. So you think the rebar in the XFMR mounting pad should be bonded to the GEC?
The pad is not in direct contact with the earth-it’s on an elevated floor level.
 
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Dale001289 said:
Thanks Don. So you think the rebar in the XFMR mounting pad should be bonded to the GEC?
The pad is not in direct contact with the earth-it’s on an elevated floor level.
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A pad is not a footing or foundation and the rebar in a slab is not a grounding electrode. There is no need to bond it. However a grounding electrode is required for the secondary of the transformer.
 
don_resqcapt19 said:
A pad is not a footing or foundation and the rebar in a slab is not a grounding electrode. There is no need to bond it. However a grounding electrode is required for the secondary of the transformer.
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"Foundation" is not defined in the NEC. I think if you have enough rebar in concrete to qualify as a CEE per code, you can and might as well use it as a CEE. It's not like physics cares what's on top of the concrete.
 
jaggedben said:
"Foundation" is not defined in the NEC. I think if you have enough rebar in concrete to qualify as a CEE per code, you can and might as well use it as a CEE. It's not like physics cares what's on top of the concrete.
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He said the pad is not in contact with the earth so it the rebar in the slab or pad can't be a grounding electrode.
 
hillbilly1 said:
But if the secondary is ungrounded as the op said, where would it go? (GEC)
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To the marked terminal on the transformer, if there is one, I presume. Or as 250.30(B) says (abridged): " A GEC ... shall be used to connect the metal enclosures of the derived system to the grounding electrode... This connection shall be made at any point on the SDS from the source to the first system disconnecting means. ... "
 
I just found out; construction failed to provide a GEC on the secondary side of the delta delta ungrounded 15kV-480V 2000kVA XFMR- they said it wasn’t required and grounded the primary side disconnect switch instead
Clearly this is a violation of 250.30(B)?
 
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