Hoping for an exception

[shockin]

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

The new 480 - 208 xfmr will be in the same place as the old POCO xfmr this location is 175' (down the exterior wall) from where I will be bringing the new 480v service in. The reason for this is avaiable realesate in the building. The distance between the old POCO xfmr and the 208 SB is 150'. This is because the SB is located in the middle of the buildling.

It would have been much easier to install a second service to the building from the POCO but they have a rule that the two services must be seperated by 300'. Talking with their engineers they weren't going to give me an exception for this.

Pictures are worth a thousand words, but the chances of me being able to correctly paste something here are slim and none.

 

[shockin]

"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...

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.

Making it lockable wouldn't be a problem

 

[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.

Outside my ongoing topic of possible multiple feeds to the building that may not be allowed:

Is the 1600 amp breaker at/near the transformer or is it the main in the existing 120/208 switchgear? If it is at/near the transformer you will have no choice but to provide separate neutral and EGC beyond that breaker.

If the first disconnect is the existing switchgear you will have to have bonding jumper installed there if you don't have a separate EGC with the feeder otherwise you will have no EGC at all except for the EGC provided to the transformer with the primary conductors which would not be permitted to be used as secondary EGC if in separate raceways.

240.21(4) will allow the outdoor secondary conductors to not have overcurrent protection until they enter the building.

Your transformer case will need to be bonded to the secondary grounded conductor somehow. This means either a bonding jumper at the transformer or an egc running back from the first disconnecting means - which is what you were trying to avoid to begin with.

250.30(A)(1) exception 2 will allow a bonding jumper at both the first disconnecting means and the source if there are no other parallel paths. I don't know of a way to get around the required EGC from the primary circuit supplying the transformer though, so I think this exception is somewhat pointless as it would create a parallel path.

 

[kwired]

The new 480 - 208 xfmr will be in the same place as the old POCO xfmr this location is 175' (down the exterior wall) from where I will be bringing the new 480v service in. The reason for this is avaiable realesate in the building. The distance between the old POCO xfmr and the 208 SB is 150'. This is because the SB is located in the middle of the buildling.

It would have been much easier to install a second service to the building from the POCO but they have a rule that the two services must be seperated by 300'. Talking with their engineers they weren't going to give me an exception for this.

Pictures are worth a thousand words, but the chances of me being able to correctly paste something here are slim and none.

So the transformer is either in, on , or immediately adjacent to the building. If so it is or can be easily made (if you have a picky inspector) part of same building. If that is the case we can disregard the violation of multiple feeders supplying one building. But at same time since it is not a feeder supplying a separate building we can not use the exception to 250.32(B). But we can still bond at the first disconnect as I mentioned in my last post if there are no parallel EGC paths, again I don't know how to avoid being parallel with the primary EGC unless it is same conductor because primary and secondary are in same cable, raceway, wireway etc.

 

[the blur]

2500A 208Y service !! I'm surprised that wasn't designed with 480Y to feed the HVAC and other heavy equipment.

I just installed some 20 TON HVAC's, and were wishing it was 480V. The job would have been cheaper and easier. And now their 800amp 208Y service is maxed out.
But I guess to bring in a 480Y after the fact is some what difficult. I would press the POCO to leave the existing 208Y, and just start new.

 

[shockin]

Is the 1600 amp breaker at/near the transformer or is it the main in the existing 120/208 switchgear? If it is at/near the transformer you will have no choice but to provide separate neutral and EGC beyond that breaker.

If the first disconnect is the existing switchgear you will have to have bonding jumper installed there if you don't have a separate EGC with the feeder otherwise you will have no EGC at all except for the EGC provided to the transformer with the primary conductors which would not be permitted to be used as secondary EGC if in separate raceways.

The new (havent bought anything yet)1600a switch I am proposing to place next to the 500kVA xfmr. There is a main breaker located at the 208v S/B which I could use instead as my disconnecting means and, as you mentioned, this would provide the benefit of possibly eliminating the need for the EGC's. The reason I was proposing to provide a new 1600a switch next to the xfmr was to protect transformer. I realize this can be acompolished onthe primary saide as well. The other side note is the the MB in the 208 S/B os actually 2500a. There are also 2500 amps worth of conductors between the 208 S/B and proposed xfmr. I don't think that really changes anything though.

 

[shockin]

So the transformer is either in, on , or immediately adjacent to the building. If so it is or can be easily made (if you have a picky inspector) part of same building. If that is the case we can disregard the violation of multiple feeders supplying one building.

Correct it is outdoors and immediately adjascent to the building. I guess I am not following the need for it to be "part of the same buildling." It's not uncommon for us to place a 480 to 208 transformer outdoors for a varity of reasons, heat and noise being the leading factors and I never thought twice about it.

 

[don_resqcapt19]

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.

David,
I don't think that the location of the system bonding jumper makes any difference. You still need a bonding conductor between the transformer and the location of the system bonding jumper. If there is no fault clearing path between the system bonding jumper and the transformer, a secondary winding fault or a secondary conductor fault at the transformer could leave the transformer case energized.

 

[Cow]

Wow, if ever a thread needed a diagram or pic, this would be it. Nothing else to add, looks like everyone else has it covered!

 

[shockin]

Wow, if ever a thread needed a diagram or pic, this would be it. Nothing else to add, looks like everyone else has it covered!

Yeah - Sorry about that. I would be glad to send someone a PDF or TIF if they were willing to post it for me.

 

[kwired]

Correct it is outdoors and immediately adjascent to the building. I guess I am not following the need for it to be "part of the same buildling." It's not uncommon for us to place a 480 to 208 transformer outdoors for a varity of reasons, heat and noise being the leading factors and I never thought twice about it.

I got off track early in the thread because you said it was going in same location as previous POCO transformer that fed it. This was for some reason in my mind looking like it was at maybe back of a lot and an old lateral that ran across the yard to the building. If that were the case you may have a hard time convincing the inspector that this is not a separate structure, but you have cleared that up enough that I'm convinced it is a part of the structure it is associated with.

 

[shockin]

David,
I don't think that the location of the system bonding jumper makes any difference. You still need a bonding conductor between the transformer and the location of the system bonding jumper.

Do you? Is this really any different then your SE arangement from the POCO where there is no bonding conductor between the xfmr and the system bonding jumper?

 

[augie47]

Do you? Is this really any different then your SE arangement from the POCO where there is no bonding conductor between the xfmr and the system bonding jumper?

don, we may be wrong, but I am of the opinion that exception 2 of 250.30
takes care of this, and the grounded conductor serves as that "bonding conductor".

 

[don_resqcapt19]

Do you? Is this really any different then your SE arangement from the POCO where there is no bonding conductor between the xfmr and the system bonding jumper?

Electrically it is no different, but code wise there are major differences.

 

[don_resqcapt19]

don, we may be wrong, but I am of the opinion that exception 2 of 250.30
takes care of this, and the grounded conductor serves as that "bonding conductor".

We really need a drawing, but I don't see that exception as applying as there will be a parallel path via the 480 volt grounded/grounding conductors.

Exception No. 2: A system bonding jumper at both the source and the first disconnecting means shall be permitted where doing so does not establish a parallel path for the grounded conductor. Where a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.

 

[shockin]

I tried attaching a PDF to this post. Hope it worked!

 

[kwired]

Can you afford to lose some capacity at the 120/208 switchgear? Like reduce the supply to 1200 amps? If so you could re arrange connections of existing conductors, since you have non metallic raceway (metal elbows may be a problem if you have those) you are permitted to run each phase in a different raceway but you still need an EGC in each so you will have 3 conductors per phase per raceway plus EGC but will have 2 extra raceways with conductors in them.

Since you have added the 480 volts supply it is possible you are moving some of the original load to the 480 supply, but I guess you don't necessarily have to either.

 

[shockin]

Can you afford to lose some capacity at the 120/208 switchgear? Like reduce the supply to 1200 amps? If so you could re arrange connections of existing conductors, since you have non metallic raceway (metal elbows may be a problem if you have those) you are permitted to run each phase in a different raceway but you still need an EGC in each so you will have 3 conductors per phase per raceway plus EGC but will have 2 extra raceways with conductors in them.

Since you have added the 480 volts supply it is possible you are moving some of the original load to the 480 supply, but I guess you don't necessarily have to either.

I hadn't consider that option. You are correct that we will be sheding a little of the existing load with the 480v and moving forward most additional loads should be 480v. I would be cutting it a little close though. The peak demand right now is 925amps as per the POCO's meter. There actual usage is roughly 60% of that.

 

[augie47]

don is awfully sharp and he may have a point in his post #35 but, so far, I fail to see the problem. I had always thought the "parallel path" wording was such as to prevent your metallic conduit from carrying current along with your grounded conductor. I will have to spend some time to see the
"Parallel path" with the 480 system.

 

[kwired]

don is awfully sharp and he may have a point in his post #35 but, so far, I fail to see the problem. I had always thought the "parallel path" wording was such as to prevent your metallic conduit from carrying current along with your grounded conductor. I will have to spend some time to see the
"Parallel path" with the 480 system.

I also mentioned the parallel path earlier in the thread, and never did see how one could use the exception that allows to have a bond at the transformer X0 as well as at the first disconnect. True if there is no potential parallel path this rule makes sense. If you have a metallic enclosed transformer you have to connect it to the primary circuit EGC and there is where a parallel path is made. The only way I can see this rule being acceptable is if the transformer would have a non conductive enclosure. How many of those have you seen, outside of small power supplies for electronic equipment?