Grounding problem

[Jorge medina]

I install a new panel out of one existing transformer 150 kva delta to star system , after I energize the panel , I found a problem one of the recept the hot side the isulation was rip and it was in contact with the metal box and send power back to the neutro bar of the pnl. I isolate the wire of the box and clear the problem.
Now this is my problem ; the breaker never trip,I check all the neutro system out of the transformer I check the ground system every looks fine the only ground I don't see is the one going from the transformer to the existing 400 amp pnl on the secondary side. They use the emt counduit like a ground from xfrm to the pnl
This confuse me, looks like a floating ground but now I not really sure. Any ideas?

 

[augie47]

sounds like XO hs not been bonded to the equipmemt grounds. Is there an XO bond jumper in the panel or transformer

 

[augie47]

 

[Jorge medina]

Looks like they used the conduit like ground but i don't remember a ground from body of transformer to xo they have only one ground from switchgear to xo.

 

[augie47]

The conduit might well be the bonding jumper to the panel, but there must be an XO to grounding connection at the transformer or panel (as shown in the sketch) for a path back to XO in the event of a grounding fault.

 

[Jorge medina]

I think you are right .I going to need to add a ground from the existing 400 amp to the xo of the xfrm. thanks for your help.

 

[augie47]

You might also check for the required grounding electrode conductor connection.
A quick review of 250.30 might prove helpful.