480V 3ph corner ground Delta system

F

Flying Wireman

Member
Location
Chicago
Occupation
Supervising electrician
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!
 
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 :ROFLMAO: )
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
 
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!
 
Since there was a fuse. Your sure it's a grounded delta. On an ungrounded 3 wire delta there would be a fuse. If one leg became grounded unintentionally by accident it would be come grounded system.
Just thought I would mentioned it before you remove fuse etc.

You did say dead short on a feeder.
Some of those old systems were ungrounded systems.
 
Tulsa Electrician said:
Since there was a fuse. Your sure it's a grounded delta. On an ungrounded 3 wire delta there would be a fuse. If one leg became grounded unintentionally by accident it would be come grounded system.
Just thought I would mentioned it before you remove fuse etc.

You did say dead short on a feeder.
Some of those old systems were ungrounded systems.
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I agree.
Make sure of what you have.
 
If it was ungrounded it was supposed to have fault indication.

Fuses are not permitted in the ungrounded conductor, Switches, circuit breakers, contactors, etc. are permitted as long as they simultaneously open all ungrounded conductors of the circuit as well.
 
jim dungar said:
Only if it is a fairly new installation. I know 50 years ago fault indication was not required.
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I kind of wondered if maybe that wasn't always required. I remember installing ungrounded system for a single piece of equipment, back before I really understood what was really going on with it. I know it never had fault indication, but sometime later on wondered if it should have had it. This probably somewhere around 1990 to 1993 when that would have been installed. That product line and most associated equipment is long gone. I still do work at that facility, different owner and different products being made there now. The Delta-delta transformer is still there collecting dust, in a room of stuff that occasionally we take something out of and put to use if we find a need for it.
 
jim dungar said:
Only if it is a fairly new installation. I know 50 years ago fault indication was not required.
Click to expand...
That rule first appeared in the 2005 code, so an old ungrounded system may not have ground detectors.

Most that I have worked on had some type of ground detection, but was not required by the code. For a 480 volt system, the ground detection was typically 3 sets of 240 volt lamps connected in series, and the sets connected in a wye with the center of the wye connected to ground.
 
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