Corner grounded delta w/reestablished ground

Status
Not open for further replies.
B

Bam

Member
I believe the system is a Corner grounded delta because of the voltage readings. This building is over 30 years old. There is no ground wire from the service disconnect to the detached sub panel. There is a reestablished ground, using 1 ground bar. The customer would like a couple three phase air handlers and three phase AC units hooked up. My concerns are, is this just wrong, grandfathered in and dangerous, grandfathered in and safe, or should the subpanel feeders be pulled out and a ground added?
 
For clarification: No "ground" wire meaning no equipment ground ??
"Detached" subpanel meaning in a separate building ?
 
Yes to clarify there’s no equipment ground from the service disconnect to the sub panel and the sub panel is in a different building.
 
With it being a corner grounded system I will look forward to replies from others but it appears as it it might comply with the Exception to 250.32
I would make sure all the requirements are met especially no other metallic paths.
 
I changed a service for a neighbor. He had a circuit out to his chicken coop that had a grounded conductor (neutral) and no EGC. I brought the wire into the panel when I changed the service but I told him if he wanted to run it he would have to make the final connection to the breaker himself, I would not do it because of the no EGC. He did tie it in himself, probably did the original install of it all.

The outbuilding, the grounded conductor would be insulated and you would not want to reestablish the ground (Earth contact and exposed bonded metal) to the grounded conductor out there. If you go floating neutral, any short to ground will cause the exposed bonded metal to float at the line Voltage, the Earth being not a EGC and not passing enough current to trip the OCPD.

Trying to trip the upstream OCPD in that event by bonding the neutral (grounded conductor) to the exposed metal bonded to the EGC (effectively the second system bonding jumper) and doing so with an industrial type corner grounded delta, is just whack. Possibly there is some code allowance for it idk and would not guess at, but even a code allowance would not make it less whack..

You need a fourth conductor to carry fault current, sufficient to trip the upstream device when necessary.
 
To clarify.
The three phase three wire corner grounded feeder is ran to another building. You are asking if an wire type EGC is required with the feeder.
And/ Or, if you are required to have a GEC at the new building.
What type of raceway is used for this feeder.
 
Tulsa, Yes the three phase three wire corner grounded feeder is ran to another building. Yes, I’m asking if an wire type EGC is required with the feeder. When the job was done originally 30 some years ago they had a ground rod at the subpanel for their grounding.
 
The raceway is a 2” pvc conduit. I think I should probably try to pull the feeders out and add a ground, it’s only about a 50 foot run but it’s been in the ground for a long time.
 
If there is any metallic system also taking the same path to the outbuilding, waterline, conduit, even a metal connecting fence, it will carry a share of the neutral current when you rebond the grounded conductor to the Earth and the remote EGC system. The rebond is a second system bonding jumper and will share the neutral (grounded conductor) current with any and all parallel paths.

Probably be pretty noisy and radiate noise for normal high current, neutral current on a parallel path.

Likely you can direct bury the EGC seperately but near to the feeder run, if you don't want to disturb the feeder just add it near to on the same run. Then the grounded conductor would float insulated at the remote point.
 
Dan, there probably is metallic pathways to the outbuilding, it sounds like you’re saying there should definitely be a ground to the service.
 
Nothing wrong with corner grounded delta.

Present code.

All feeder circuits require an egc. Does not have to be a wire.

A grounding electrode system is required at each structure served by a feeder downstream of the service. The ges is bonded to the egc.

There should not be a connection from earth to the grounded conductor of the corner grounded system except at the service point.

Previous codes may have allowed what is there. I am having a hard time following exactly what you are saying but I think the gist is no egc with the feeder to the outbuilding and ges at outbuilding connected to grounded conductor.
 
Bam said:
Tulsa, Yes the three phase three wire corner grounded feeder is ran to another building. Yes, I’m asking if an wire type EGC is required with the feeder. When the job was done originally 30 some years ago they had a ground rod at the subpanel for their grounding.
Click to expand...
250.32(B) is what needs to be compiled with. The last code cycle that allowed re-bonding the neutral/grounded conductor at a separate structure supplied by a feeder was 2005.
 
Status
Not open for further replies.
Top