Transformer grounding electrode

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First timer here. Not sure how this all works. I wanted to ask a question about Seperately Derived Systems (SDS). We have 2 PDUs (Power Distribution Units) in a data center that have been in operation since the 80s. We recently expanded the data center and added 3 more PDUs. We received a red tag on the installation because the PDUs did not have a bond to building steel. The originals do not either, at least in that vicinity. The originals bond via a ground in the primary conduit back to the service equipment. The service equipment is bonded to building steel. I know the original installation passed inspection (in the 80s) and I was wondering about the bonding of the SDS to building steel in the local vicinity and if we should change the way the original PDUs are bonded?
 
Greg, You need to run a GEC from your SDS's to building steel to ground the

XO terminal. As far as the existing PDU's it's never been compliant to use the

primary EGC as the GEC for the secondary side, BUT, some of the EE's on this

Forum feel that it is still a safe installation.
 
benaround said:
MarkWhite, I wonder how you size the EMT to the secondary conductors of

the SDS ?

Also see post# 11.
Click to expand...


He said this:

One inspector said that he allowed the use of the EMT feeding the 480v panel to carry the GEC back to the main service. The GEC between the 480v panel and the SDS xfmr was sized based upon the secondary conductor size.
Click to expand...

Sounds like he's allowing the EMT to "carry" the GEC within the EMT, and sized according to the secondary conductors. He's not using the EMT as the GEC.
 
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