Resin Encapsulated Transformer

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Sparky3141

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I recently got a call from a customer who used an Ideal Circuit Analyzer to check the ground impedance on his system to discover that it was high. The tester didn't identify how high it was, just that it was over the expected value. When I got over there I found an old Westinghouse resin encapsulated 15kVa, 480 to 208/120 transformer. I could not find an SBJ on the transformer and at the time I suspected that it was internal. Neither was there a terminal bar anywhere on it. So what I did was (temporarily) bond the neutral to the EGC and it cleared the circuit analyzer?s ground impedance test failure.


Never having installed an encapsulated transformer before, I?ve been scouring the internet for information but alas to no avail. After having thought about it though, I don?t know why I can?t just install a grounding and bonding terminal bar, land my neutral, ground (oh yeah, not grounded either), SSBJ and call it a day. Anyone know *for sure, for sure* if this thing might have been designed internally bonded?
 
Can't say *for sure, for sure*, but I doubt it was internally bonded.

Being the temporary jumper cleared the failure, I doubt it has an SBJ, but just in case, did you check the first disconnecting means or any intervening junction boxes for an SBJ? The SBJ and GEC connection must be in the same enclosure when dealing with a separately derived system

Another [remote] possibility might be it is a high-impedance grounded neutral system [250.36], but ground detectors are required and system cannot serve any line-to-neutral loads.
 
Sparky3141 said:
..... After having thought about it though, I don?t know why I can?t just install a grounding and bonding terminal bar, land my neutral, ground (oh yeah, not grounded either), SSBJ and call it a day. Anyone know *for sure, for sure* if this thing might have been designed internally bonded?
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That's what would do. I have never seen an encapsulated transformer that was internally bonded. If there was one I would expect it to see something on the nameplate about it.

Besides that, if it was internally bonded under the resin, one more connection to the case of the transformer would only be redundant. There would be no objectionable current. Like Smart said you would have to check the first disconnect.
 
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