Sub panel in remote building revisited

[dhalleron]

Sorry so long. I've been through this before, but I need another reminder.

I looked at a job today that needed a panel replaced. Seemed like a simple job until I looked closer.

I need to get a permit for this and want to make sure it is correct. I haven't asked the inspector what he will allow yet.

Two buildings 50 feet apart under same ownership.

First building:

Has the existing service probably 30 years or more old with a trough feeding 5 meters with fusible 100 amp disconnects under them. Driven ground and water ground are here.

4 EMT conduits from disconnects into the dirt feeding 4 main lug only panels in remote apartment building. Who knows what conduit is run under the parking lot. Probably rusted out EMT.

Remote apartment building:

EMT conduit in the wall and probably coming out of the slab to main lug only panel.

Remote building has no driven ground or water ground.

Panel has 3 #2 AWG conductors only. No ground except for what it might get from the conduit. The branch circuit grounds and neutrals are under the same bar. The feed #2 neutral conductor was marked green by somebody.

This remote building has a total of 4 apartments with panels wired the same way.

If I replace this panel, can I just bond the neutral to the panel and put the grounds on the same bar? Is there a need for a driven or water ground?

No telling what code this was installed under and was it ever correct? I?m looking at Article 250 of 2005 NEC. The metal conduit underground seems to be the thing that might make me need to install a grounding electrode at the remote building.

Any other thoughts on this?

Thanks.

 

[Dennis Alwon]

If there is no metallic pathway between the two building then only three wires are needed however I bet there may be water lines and phone lines that go between buildings and this would mandate a egc. Now if the emt is indeed intact it can be the egc. You would then need to separate the egc from the neutrals and drive 2 rods. You would also need to bond any metal pipe that is in the ground for at least 10 feet. This would be your main grounding electrode. This and the rod GEC get connected to the egc which, again is separated from the neutral.

 

[dhalleron]

Thanks for the input.

I spoke to the chief electrical inspector. There were some other problems with the existing 1960's install that he would not pass if I tried to replace just this one panel.

1. He wants 4 conductors instead of 3. That might mean cutting a parking lot.
2. He wants the 4 disconnects grouped on the wall outside the 4-plex. Currently they are on another building.
3. The neutrals and grounds need to be separated in the other 3 apartments also.

Looks like I won?t be doing this job. The customer only wanted to spend the money to replace 1 panel.

 

[tjelec]

Sounds like the electrical inspector is correct. It being a single service for the buildings, it only receives one bond which should be at the main service disconnect for the original service or perhaps upstream. This should be the only bond if this is the only created neutral. You would then have to pull grounds out to each panel and isolate the neutral bar from the ground. As far as your question about bonding the neutral in each panel, you essentially already had a double bonded neutral before with all the grounds landed on the neutral bar.

Thanks for the input.

I spoke to the chief electrical inspector. There were some other problems with the existing 1960's install that he would not pass if I tried to replace just this one panel.

1. He wants 4 conductors instead of 3. That might mean cutting a parking lot.
2. He wants the 4 disconnects grouped on the wall outside the 4-plex. Currently they are on another building.
3. The neutrals and grounds need to be separated in the other 3 apartments also.

Looks like I won?t be doing this job. The customer only wanted to spend the money to replace 1 panel.

 

[Dennis Alwon]

Sounds like the electrical inspector is correct. It being a single service for the buildings, it only receives one bond which should be at the main service disconnect for the original service or perhaps upstream. This should be the only bond if this is the only created neutral. You would then have to pull grounds out to each panel and isolate the neutral bar from the ground. As far as your question about bonding the neutral in each panel, you essentially already had a double bonded neutral before with all the grounds landed on the neutral bar.

TJ, before 2008 code this may have been a legal install. The NEC only required 3 wires, for single phase, to a detached structure and the neutral was bonded to the can. There the ground rods etc were tied also.

 

[tjelec]

Legal before or not it should be changed, its parralleling the ground which is dangerous and doesn't always produce enough of a fault to actually trip out.

 

[Pierre C Belarge]

The code requirements you are looking for are located at 250.32. Check this section closely, as it has changed in the '08 code if you are referencing that code.

It seems to me this installation has been incorrectly installed. How you resolve this will depend on the code you are following now.
Which code cycle are you referencing?