480V 3ph corner ground Delta system

[Flying Wireman]

We're working on a repair job in an old warehouse, that has a 480V 3ph corner ground Delta systems and I have a few questions since this is the first time I'm encountering this type of system.

There was a dead short on a 200A feeder, and we need to run new conduit and 200A feeders from the existing switch gear (installed in 1955) to 2x transformers which are tapped off this feeder.

1) I noticed that the B phase (grounded) was fused, and my first thought is that it shouldn't have been (240.22 ). This was the case both in the switchgear and the fused disco on the transformer primary. I'm assuming that is something I need to fix by placing a copper plate on the B phase in all locations except motor discos??

2) The two transformers that are tapped of 200A feeder don't have any wires marked, and wiring diagram no longer available. These are step down transformers 480V --> 120/208 Y.... so my question is: Does it matter which terminal on the primary side (H1, H2 or H3) gets the grounded phase, since all of them have 480V?

3) In terms of transformer grounding, EGC from switchgear to transformer case, and X0 (secondary side) bonded to transformer case. Also run a GEC to the nearest qualifiying GE. This seems standard to me, just wandering if there is anything else I might miss?

4) Is this a type of installation that should be supervised by an on-site electrician?

Thanks!

 

[zbang]

1) yes, replace the fuse with an approved bridge or wire around it (I've seen copper plumbing pipe with the ends flattened out, but that's not a listed use )
2) no, I'm assuming the primaries are delta-connected
3) sounds right to me
4) not really, there are lots of corner-grounded delta systems out there, IIRC they're quite common for farm irrigation systems

 

[ptonsparky]

Those approved cu plates cost more than fuses.

 

[Jraef]

Were they actual fuses or “dummy” fuses that are used in lieu of fuses on corner grounded systems?

 

[mayanees]

Yes to the pipes for fuses. This takes me back 42 years to when I started at the DuPont facility in Parkersburg, WV. An old electrician was showing me around, and he showed me how to tell which corner is grounded by using just his thumb. The callous was such that he could tell a grounded phase from an ungrounded phase by touching it! Oh how things have changed!