Transformer bonded improperly

[joeyww12000]

I have noticed on 2 out of 3 jobs Ive been with my company noone bonds there transformers creating seperately derived systems correctly. Yesterday I took the cover off of a step down transformer 480/120-208v because I didnt see a GEC leaving the transformer nor the 120/208v panel it fed, so I became suspicious. I find in the transformer an attempt to bond. I saw a EGC coming in with the feeders tied to a lug that was attached to the case of the xfmr which was fine except there was a bonding jumper from xo and the EGC leaving with the derived phase conductors under that same lug. No the lug was not rated for multiple conductors also there was no GEC anywhere, the system grounded conductor was bonded via the EGC with the xfmr feeders. I know this isnt correct, but theoretically where would the fault current go on a downstream fault on the load side of the xfmr on this setup? Current leaving the xfmr returns to the xfmr, would the egc in with the feeders carry this current if it was of sufficient size....which its not but theoretically?

 

[joeyww12000]

I guess what Im asking is what are the hazards of this setup and what would happen under fault conditions?

 

[brian john]

Assuming the manufacture does not have a neutral/XO to ground bond in place.

Well the first fault is free, nothing would happen but assuming "C" phase faults. Voltage would be "A" to ground 208 VAC, "B" to ground 208 VAC, "C" to ground ZERO (0) VAC (or close to zero), neutral to ground 120 VAC. This is assuming a 208/120 VAC Wye system.