high leg bonding?

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bill@usps06492

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I've been working in this older commercial building that has 120/240-208v 3ph delta service with a single throw 400a main disconnect switch. The voltages are 240v between phase ab,bc,& ac, and from either a or b phase it's 120v to the neutral & ground. On phase c it's 208 to neutral & ground. Are there any special requirements for bonding grounds and neutrals in these systems? There are panels in this facility that have the neutral and ground landed on an isolated neutral bar, and in the same panel there is a ground bar that is isolated from the panel and not bonded to the neutral. It has always been my understanding that once your out of the main service disconnect the neutral is isolated from the panel and the ground. They are only bonded together at the service disconnecting point. I haven't found anything in the NEC to lead me to believe that a delta system should be bonded and grounded any differnt. My concern is that if I start to correct these, can something happen with the system voltage? Thanks Bill
 
One of the problems I see is making sure that some of those green wires are indeed EGC and not a GC. If the installer did not take the time to connect them to the correct bar, they may not have worried about the correct color either.

Have fun. You won't change the charactersitics of the high leg delta by correcting improper grounding/bonding practices of others.
 
There are no special grounding requirements for a delta system and the only time the neutrals and grounds should bond together after the service in the same building is at a seprately derived system.
 
If this is a medical or telco/data site, you may have an isolated ground. Be sure that both the ground paths are connected to the source (the metal conduits and the cabinet) if the grounds are green with a yellow strip this would be a clue that it may be an isolated ground.
 
This was originally an auto/truck repair facility built in the late 60's early 70's. This is not a medical or teleco site.
In the panel that is next to the main disconnect there is an identified neutral, #2awg with white tape and a bare copper ground, looks like a #4. Both of these are landed on the neutral bar that is isolated from the panel. (This panel has a 100A main breaker) Next to the neutral bar, in this panel, is a smaller ground bar with green, bare, and black wire w/green tape, copper #12 & #10, (approx 12 in total) that are for circuits leading out to lights, recp, and A/C-heat unit. But this ground bar is also isolated from the metal panelboard.
In the other panelboards that have a EGC, the grounds and neutrals are all landed on the same bus, and the neutral bars do not appear to have a bonding screw tying it into the metal panelboard, as they should not, since these are all sub panels off the main.
There are a total of 4-3ph@100a & 2-1ph@70a panels, all are main lug with no main breaker, except the panel nearest to the 400a main disconnect.
I hope these extra details will help.
Thanks Bill
 
Bill, I'm short on time right now, but the best advice I can give you is that, except for the high leg (which is 'high' only because of which conductor we choose to bond), a high-leg Delta service is otherwise identical to a typical 120/240v service.
 
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