Is my panel wired correctly?

[Number22]

My shop is in a small industrial complex, I share a power meter with a few other shops. I am in a seperate building than the other shops and I have my own 100 amp 3 phase 208v subpanel.

The wires coming from the other building come in underground through a PVC conduit. There are 3 hots, and a neutral, but no ground between my building and the other building, or between my building and the meter. There is a seperate earth ground attached in the panel. Also the ground/neutral in my subpanel are bonded, with the ground wires and neutrals all hooking into the same bus.

Is this the way it is supposed to be? Or should there be another ground between me and my power meter? Normally a building would have two grounds, the utility ground and the earth ground...but I only have the earth ground.

 

[Number22]

Anyone? Does a dedicated ground wire need to be run between buildings and the meter, or is the neutral + an earth ground good enough?

Also should the neutral/ground be bonded together? I thought they shouldn't be in a subpanel, although this subpanel is feeding an entire building all to itself.

 

[mrb]

there should be a ground for a total of 5 wires going to your panel, and the neutral and ground on seperate busses, but it may have been ok the way it is when it was installed. How old is it?

 

[mrb]

out of curisoity, is it 120/208Y or 120/240 Delta?

 

[MN BIANCHI]

Check out this link for an explanation of Delta vs. Y 3 phase connections.
http://en.wikipedia.org/wiki/Three-phase_electric_power

 

[Number22]

It's 120/208Y service. I believe it was put in around 1995 but they didn't bother following many codes anywhere.

Code issues aside - is that SAFE?

 

[mrb]

Check out this link for an explanation of Delta vs. Y 3 phase connections.
http://en.wikipedia.org/wiki/Three-phase_electric_power

if that was for me, i am well aware of the different systems. I was asking the OP what his shop had. Alot of the smaller industrial spaces have 120/240 3P4W Delta (or High Leg as some call it) service, while others have the 'normal' 120/208Y. In fact where I am you cant even get 120/208Y unless you have primary service and your own transformer, all theyll give you is delta.

 

[mrb]

It's 120/208Y service. I believe it was put in around 1995 but they didn't bother following many codes anywhere.

Code issues aside - is that SAFE?

safe is subjective, I will say its not good since you will have current flowing on metallic paths in the building not just on the neutral where it belongs.

 

[Number22]

In fact where I am you cant even get 120/208Y unless you have primary service and your own transformer, all theyll give you is delta.

I think that's what we have, one transformer for the big main building + me. All the other industrial neighbors seem to have their own too.

I almost want to see if I can get my own seperate 120/240 single phase service and my own meter. 3 phase is cool but I want a full 240v!

 

[Number22]

safe is subjective, I will say its not good since you will have current flowing on metallic paths in the building not just on the neutral where it belongs.

So in other words go nuts with the GFCI outlets/breakers like I'm doing?

 

[mrb]

So in other words go nuts with the GFCI outlets/breakers like I'm doing?

that wont change the fact that you have parallel paths for neutral current from your panel back to the main.

 

[mrb]

I almost want to see if I can get my own seperate 120/240 single phase service and my own meter. 3 phase is cool but I want a full 240v!

if you REALLY need 240v for some reason you can use a transformer....but have it installed by a qualified professional.

 

[sparky1562]

If there are no other "electrically continuous paths" between the two buildings, it is okay. The code used to say that this method was acceptable. Then we started running phone lines, cable lines, etc. The last code revision to the NEC now says you have to pull the ground wire, no option, IIRC.

You will find a lot of buildings fed the way yours is. Fault current will follow the path of least resistance, which will be the ground wires in your building, or via the earth ground connection back to the Neutral and the breakers will trip. While fault current will run on all paths it finds, not very likely that a separate electrically continuous path between the buildings will constitute a safety issue, IMHO.

 

[sparky1562]

safe is subjective, I will say its not good since you will have current flowing on metallic paths in the building not just on the neutral where it belongs.

Normal current will not. If the building is metal it should be bonded to the panel, and any metal piping within the building should be bonded to the ground bus in the panel as well, if it is not already. If it isn't, that would be unsafe.

 

[Number22]

any metal piping within the building should be bonded to the ground bus in the panel as well, if it is not already. If it isn't, that would be unsafe.

Hmmm...how would I go about checking that? The building is made out of concrete and concrete blocks, 99% of the plumbing is burried in it.

 

[sparky1562]

If it has a water service, with metal piping, you can bond to the metal pipe where you can get to it. (assuming the metal piping is continuous with no dielectric unions, bond it once. If not, jumper across any dielectric or non-metal joints) (If the metal pipe is the grounding electrode, must be bonded within 5ft of where it enters the building).

Any interior metal piping system should be bonded to the grounding electrode conductor via a #6 for a 100 amp feeder.

 

[freebeer]

No, your panel is not wired correctly. Neutrals and grounds should not be bonded in any subpanel which is what you have. The easiest way to fix this is to seperate your neutrals from your grounds, get an isolated neutral bar for the neutrals (the fourth feed wire is actually a neutral not a ground.) Bond your grounds to the panel. and install a seperate ground system ie: ground rod, rods or a ground ring whichever is required by your power company/local code.

 

[sparky1562]

No, your panel is not wired correctly. Neutrals and grounds should not be bonded in any subpanel which is what you have.

If the feeder does not contain a ground, which this one doesn't, the neutral has to be bonded, otherwise there is no low impedance ground path back to the source. This was allowed in all but the latest code revision, which now requires a ground to be pulled, no exceptions anymore. The only question is whether there is any other electrically continous paths between the buildings.

 

[mrb]

No, your panel is not wired correctly. Neutrals and grounds should not be bonded in any subpanel which is what you have. The easiest way to fix this is to seperate your neutrals from your grounds, get an isolated neutral bar for the neutrals (the fourth feed wire is actually a neutral not a ground.) Bond your grounds to the panel. and install a seperate ground system ie: ground rod, rods or a ground ring whichever is required by your power company/local code.

your suggestion would create a very dangerous situation. I suggest you read up on the subject.

 

[freebeer]

your suggestion would create a very dangerous situation. I suggest you read up on the subject.

Please, explain?

Edit: Maybe you misunderstood my suggestion. He needs to have seperate potential on grounds/ neutrals. His Neutral is incoming from the transformer or main switch gear/panel. This is the wire he already has. The seperate ground I state is to become/tie into his ground so that it is properly grounded.

 

[mrb]

Please, explain?

Edit: Maybe you misunderstood my suggestion. He needs to have seperate potential on grounds/ neutrals. His Neutral is incoming from the transformer or main switch gear/panel. This is the wire he already has. The seperate ground I state is to become/tie into his ground so that it is properly grounded.

if you seperate the neutral and ground in his subpanel and do not install an EGC along with the existing 4 conductors, back to the main (or wherever it comes from) there will be no return path for fault current. After doing this, when there is a fault a breaker will not trip as it should and whatever metal (a tool, machine, the building, etc) a 'hot' conductor comes in contact with will become energized.

The ground rods and such you proposed he install do not create a return path for fault current.

 

[freebeer]

If the feeder does not contain a ground, which this one doesn't, the neutral has to be bonded, otherwise there is no low impedance ground path back to the source. This was allowed in all but the latest code revision, which now requires a ground to be pulled, no exceptions anymore. The only question is whether there is any other electrically continous paths between the buildings.

True, but the same potential N-G still exists which is a worse situation. The only exception would be if he put in an isolation transformer. Pulling a new 5 wire feed may not be a feasible option.

 

[freebeer]

if you seperate the neutral and ground in his subpanel and do not install an EGC along with the existing 4 conductors, back to the main (or wherever it comes from) there will be no return path for fault current. After doing this, when there is a fault a breaker will not trip as it should and whatever metal (a tool, machine, the building, etc) a 'hot' conductor comes in contact with will become energized.

The ground rods and such you proposed he install do not create a return path for fault current.

Edit: my brain quit working today!

 

[freebeer]

mrb, the more I think about it, you are correct. If there is no path back to the centertap xo of the transformer, fault may not occur regardless of ground. So as long as there are no other metal paths back to the source he is OK the way he is. If there is a pathe back he has to run a fifth wire or have an isolation xformer right?

 

[Number22]

The only question is whether there is any other electrically continous paths between the buildings.

Well, there is no other wiring (phone lines, etc), but what about the plumbing? I have no idea if it's grounded properly or not, but I believe it's copper underground from the main building.


PS - is 1/0 aluminum cable big enough for 100A service? I found "1997" written on the side of the cables...

 

[sparky1562]

Well, there is no other wiring (phone lines, etc), but what about the plumbing? I have no idea if it's grounded properly or not, but I believe it's copper underground from the main building.


PS - is 1/0 aluminum cable big enough for 100A service? I found "1997" written on the side of the cables...

1/0 A is rated at 100 amps for types TW and UF. Everything else is at least 125 amps.

You said you have an earth ground in the first post. I assume this is a driven ground rod? If the incoming pluming line is metal in contact with earth for at least 10 ft (IE:not pvc underground), it should be used as part of the grounding electrode sytem. For 100 amp service, a #6 copper run from the ground bus in the panel to the water line, within 5ft of where it enters the building from underground.

If it is not metalic underground, and is PVC, just bond it to the panel in any accessible place.