Hoping for an exception

[shockin]

Dealing with a small manufacturing facility that currently has a 208v service. We are going to install a new 480v service and "re-feed" the exsiting 208v service from there.

There will be a new 500kVA 480 - 208v xfmr and 1600a switch located outdoors at the "old" 13.2kv -208 volt utility transformer location.

I am hoping to reuse the conductors between the old utlity transformer location and old 208v switch gear. My problem is, because the 208 conductors use to be the service entrance there is obviously no ground conductor. With my new set up, I will need a ground installed in these conduits. I am hoping to not pull out 150' X 4 conduits worth of 600 CU just to pull a ground in. Is there by any chance an exception that may apply here? I know that the NEC requires that that gnd to be routed with the conductors, but I am hoping I am overlooking something.

Thanks in advance.

 

[kwired]

Where is system bonding jumper located, what kind of raceway is it, where is first overcurrent protection device?

 

[kwired]

I can see some problems complying with 225.30 if you intend to supply 480 to the building also, which I'm assuming you are.

You can bring two services to a building but generally can not bring two feeders to a building.

 

[charlie b]

I don?t think you will find the exception you are hoping to find. But I don?t know of an NEC prohibition against pulling a new wire through an existing conduit with existing conductors. I know there is some risk of damage (i.e., from new insulation rubbing against existing insulation). I also know that the common practice is to pull everything out, and pull the new set through the empty conduit. But if you are talking about pulling a bare copper 4/0 past a set of 600 MCM conductors, is the risk of damage still there? This is outside my area of expertise, but it is the only suggestion I can offer.

 

[don_resqcapt19]

Are the existing raceways metallic?

 

[petersonra]

Are the existing raceways metallic?

I am a bit amazed no one asked this question first.

 

[charlie b]

Are the existing raceways metallic?

I am a bit amazed no one asked this question first.

Kwired did ask that question. See post #2.

 

[kwired]

Kwired did ask that question. See post #2.

Don't worry about it, the wife and the kids never pay attention to what I have to say either

 

[shockin]

Where is system bonding jumper located, what kind of raceway is it, where is first overcurrent protection device?

The bonding jumper that was in the 208v switchboard will be removed. It will instead be bonded in the 480v service.

It is PVC conduit so no help there.

There will be a 480v/600a breaker to protect the xfmr and then a 208v/1600a breaker to protect the conductors on the other side.

 

[shockin]

I can see some problems complying with 225.30 if you intend to supply 480 to the building also, which I'm assuming you are.

You can bring two services to a building but generally can not bring two feeders to a building.

I probably didn't explin this very well, but there will only be one service to the building and it will be the new 480v one.

I will be feeding the "old" 2500amp 208v switchboard thru a new 500kVA transformer.

 

[shockin]

I don?t think you will find the exception you are hoping to find. But I don?t know of an NEC prohibition against pulling a new wire through an existing conduit with existing conductors. I know there is some risk of damage (i.e., from new insulation rubbing against existing insulation). I also know that the common practice is to pull everything out, and pull the new set through the empty conduit. But if you are talking about pulling a bare copper 4/0 past a set of 600 MCM conductors, is the risk of damage still there? This is outside my area of expertise, but it is the only suggestion I can offer.

I don't think I would have much luck trying to pull in a new conductor with the (4) 600mcm's in there. It is approximatly 150' with (3) 90 degree bends in a 4" PVC. Sucking a line thru is about the best option, but I would be too worried about damage from the rope/pullstring as you mentioned.

 

[augie47]

It's always a bit confusing to me when one references "no ground". I assume "no equipment grounding conductor". If that be the case and as noted, the transformer is outside, I would give consideration to relocating the 1600 amp switch to the building and take advantage of 240.21(C)(4) and Exception (2) to 250.30. I believe you can work around the EGC that way.
(I imagine that is why kwired asks his questions in Post #2.

 

[kwired]

The bonding jumper that was in the 208v switchboard will be removed. It will instead be bonded in the 480v service.

It is PVC conduit so no help there.

There will be a 480v/600a breaker to protect the xfmr and then a 208v/1600a breaker to protect the conductors on the other side.

How about the bonding jumper for the 120/208 secondary?

Is the service at the location of the transformer which you mention is 150 feet away, that was originally the poco transformer location if I understand correctly.

What I am getting after here is if the transformer is a separate building or structure and it supplies another building or structure. If so you could run into some problem here with more than one feeder supplying the second building or structure.

Before 2008 NEC no separate EGC would probably be acceptable, may be up to AHJ if the exceptions for existing feeders will apply, if he allows more than one feeder in the first place.

 

[shockin]

How about the bonding jumper for the 120/208 secondary?

Well I had assumed it would be at the 480 - 208v xfmr. But I am still trying to wrap my arms around Augies previous post.

Is the service at the location of the transformer which you mention is 150 feet away, that was originally the poco transformer location if I understand correctly.

What I am getting after here is if the transformer is a separate building or structure and it supplies another building or structure. If so you could run into some problem here with more than one feeder supplying the second building or structure.

.

I am sorry but I am struggling to follow this a bit. There is one building at this location and ultimatley one feed from the poco at 480v . Are you saying that installing a 480v - 208v xfmr creates a second service? That doesn't seem correct. Or is it becuase I am locating the 480 -208v xfrm outdoors that changes some rules?

 

[david luchini]

I could be missing something, but it seems like you're describing a new 480V service and a new 208V separately derived system. Don't install the secondary switch at the outdoor xfmr. The system bonding jumper for the separately derived system is permitted to be at the first disconnecting means which is your existing 208V switchboard (250.30(A)(1)). In addition, the grounding electrode conductor connection should be made at the point where the system bonding jumper is made. The switch on the existing 208V swbd could be the disconnecting means on the SDS.

I don't see a need for an equipment grounding conductor run in the existing secondary feeder if the gec and system bonding jumper is connected at the existing switchboard. You'd have to see if the existing feeder complied with 250.30(A)(8), however.

 

[petersonra]

Is there some reason you cannot use the old neutral conductors as EGCs?

Put the new transformer downstream.

 

[shockin]

I could be missing something, but it seems like you're describing a new 480V service and a new 208V separately derived system. Don't install the secondary switch at the outdoor xfmr. The system bonding jumper for the separately derived system is permitted to be at the first disconnecting means which is your existing 208V switchboard (250.30(A)(1)). In addition, the grounding electrode conductor connection should be made at the point where the system bonding jumper is made. The switch on the existing 208V swbd could be the disconnecting means on the SDS.

I don't see a need for an equipment grounding conductor run in the existing secondary feeder if the gec and system bonding jumper is connected at the existing switchboard. You'd have to see if the existing feeder complied with 250.30(A)(8), however.

This would be exactly what I was hoping someone would say. I believe this is what Augie was saying as well.

To further complicate the matter, I would like to protect the primary side of the new 500kVA transformer from a breaker 175' away. The secondary side as you are proposing would be protected at the existing switchboard 150' away which is actually 2500a with the conductors sized accordingly. Anyone see a problem with this?

 

[shockin]

Is there some reason you cannot use the old neutral conductors as EGCs?

Put the new transformer downstream.

Bob -

I keep refering to it as 208v but it should be correctly stated as 208/120Y 3 phase 4wire. Therefore I will be needing my neutrals.

Thanks

 

[augie47]

This would be exactly what I was hoping someone would say. I believe this is what Augie was saying as well. ?

"Trying to say ?" What ? I have marbles in my mouth
(Joking) I know I'm often unlclear. Ole inspectors trick "I didn't say that" , but, yes, that was what I was saying...

To further complicate the matter, I would like to protect the primary side of the new 500kVA transformer from a breaker 175' away. The secondary side as you are proposing would be protected at the existing switchboard 150' away which is actually 2500a with the conductors sized accordingly. Anyone see a problem with this?

No problem with the primary disconnect being 175' away as far as I know, but I think the '11 Code requires it to be lockable.

 

[kwired]

Well I had assumed it would be at the 480 - 208v xfmr. But I am still trying to wrap my arms around Augies previous post.



I am sorry but I am struggling to follow this a bit. There is one building at this location and ultimatley one feed from the poco at 480v . Are you saying that installing a 480v - 208v xfmr creates a second service? That doesn't seem correct. Or is it becuase I am locating the 480 -208v xfrm outdoors that changes some rules?

You said it is in same location as previous POCO transformer and you mentioned 150 feet of raceway. Is the transformer at the building or away from building? If away from building Where is it fed from? Where is 480 volt service disconnect(s)? I would expect the supply from this transformer to come from the 480 volt service that is feeding the building and not have a separate 480 service at the transformer. You have two separate buildings or structures if they are not near each other, if they are near each other it is somewhat an AHJ call.

I know it doesn't seem right because you could have left the existing as it was and added the 480 volt service and been NEC compliant, but doing what you did makes the 208 system a separately derived system and not a service so art 225 applies instead of 230 for the 208 volt system if it is feeding a separate building or structure