# Bonding and grounding of Service confusion



## Wiresmith (Feb 9, 2013)

is your transformer at the portable building?


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## Wiresmith (Feb 9, 2013)

look at 250.32(B)(1)exceptions

and article 590 (temporary installations)

i'll re-read your first post to try to better understand what you have, i can't give you definitive answers yet


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## Wiresmith (Feb 9, 2013)

1.from what you described, i believe so

2.only bond neutral to ground in transformer if you have a metal conduit, the conduit will be your equipment gorunding conductor.

use grounding electrode at seperate structure, just tie it to equipment grounding conductor though, not the neutral


side-note:
its amusing to me they have a 3 phase transformer for single phase, what 208 load do you have at the portable?


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## rbd1313 (May 5, 2018)

The transform is about 150 feet away in the main plant building.

It's a 60 foot portable office building that will be permanent. If they'll ever use 208 I doubt it, but I try not to talk to the dip in charge it's like speaking to a politician.

Checked out the conduit Friday night and seems to be the normal PVC with Ridgid 90 ends. So I should be able to bond at either end or both without having the parallel grounding path since the transformer will get it's equipment grounds from what's feeding it and the portable will get it's from the ground rod that's out by it making no need to pull a grounding wire if I'm understanding that correctly.


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## Wiresmith (Feb 9, 2013)

by the way i understand your post you need to bond at transformer and portable, no other options. if you dont bond at the portable and have a phase to ground fault in the portable, no circuit breaker will trip, the resistance of the earth will be high enough to keep the current too low if you only use a ground rod, the ground rod is only there to dissipate transient voltage differences between earth and the structure wiring


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## Wiresmith (Feb 9, 2013)

also if you dont need 208, use wires as follow 1 hot 1 neutral 1 ground wire.

and this is not a service like your title insinuates or the section you posted it in i ask that you ask a moderator to move this to NEC section


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## rbd1313 (May 5, 2018)

After double checking the transformer turn out to be 480 to 120 or 120/240 single phase primary and secondary. So it just got feed with 2 of the legs coming off the 3p 480 power. Had to run it 120/240 for future use not my call. Sorry if this is in the wrong section I'll check with an admin. Besides not having its own meter or extra ground besides the rod its quite like coming off a pole and going under ground to feed a house so thought it would be this section.

Thanks for the information. Everything seems to be working well.


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## Wiresmith (Feb 9, 2013)

you're welcome, thanks for asking and looking it up




it would fall under separately derived system or feeder, service is where the utility connects to premises wiring


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## Wiresmith (Feb 9, 2013)

and after your done you can check current on neutral where it enters building and current on neutral at transformer to make sure you don't have a parallel path somewhere


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## varmit (Apr 19, 2009)

You will definitely need 4 conductors from the transformer to the second building - 2 hots, a neutral and a ground (bonding conductor). 

Bond the transformer neutral and all grounds and bonding conductors at the transformer. Since you are going over 50 feet and to a separate building, a disconnect is required on the load side of the transformer. 

At the remote building, there would be no connection between the "neutral" and any of the bonding or grounding conductors.


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## Wiresmith (Feb 9, 2013)

what about 250.32(B)(1) exceptions and 250.30(A)(1) exception 2


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## varmit (Apr 19, 2009)

Wiresmith said:


> what about 250.32(B)(1) exceptions and 250.30(A)(1) exception 2


For 250.32(B)(1) Exception 1 to apply the building would need to have been connected prior to the 1999 NEC.

I believe that 250.30(A)(1) Exceptions are not applicable to this installation.


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## Wiresmith (Feb 9, 2013)

varmit said:


> For 250.32(B)(1) Exception 1 to apply the building would need to have been connected prior to the 1999 NEC.
> 
> I believe that 250.30(A)(1) Exceptions are not applicable to this installation.


the way i look at it is the conduit and wire was installed already and just look at the situation as they are replacing the mobile building and transformer, i think it applies but could be wrong. i don't think 250.30(A)(1) applies to his situation either unless the transformer is outdoors just put it in there in case it was.


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## Wiresmith (Feb 9, 2013)

varmit said:


> Since you are going over 50 feet and to a separate building, a disconnect is required on the load side of the transformer.


just to be clear on this, your not suggesting he needs a disconnect between transformer and underground feeder correct?

it could just be at the portable building and be his main breaker right?


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## varmit (Apr 19, 2009)

Yes, in this installation a disconnect/over current protection would be required on the transformer secondary at the transformer. See NEC 240.21.

Also, under current code, a transformer line side disconnect is required. See NEC 450.14.


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## Wiresmith (Feb 9, 2013)

varmit said:


> Yes, in this installation a disconnect/over current protection would be required on the transformer secondary at the transformer. See NEC 240.21.
> 
> .


what about 240.21(C)(4)

i don't think it is required at the transformer, but if i'm missing something i would appreciate being corrected


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## Wiresmith (Feb 9, 2013)

varmit said:


> Also, under current code, a transformer line side disconnect is required. See NEC 450.14.



450.14
"or remote location"

says disconnect can be at remote location, which i would consider this the breaker he has before the transformer

once again i would appreciate being corrected if i am wrong on this but i believe you may be missing this


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## Wiresmith (Feb 9, 2013)

i think 250.30(A)(1) via 250.32(B)(2)(b) actually might be more applicable to the OP's situation but i'm not for sure due to lack of details which i would only need to decide which code section allows it. i'm not seeing how its not allowed.

in this setup i'm not seeing any added hazards over what normal residences side by side using the same transformer secondary and both being bonded at there first disconnect. what added hazard would there be?

or even the neutral being bonded at a utility transformer and then also at the service disconnect at the premises


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## varmit (Apr 19, 2009)

Yes, disconnect can be at a remote location as long as it is lockable without adding any temporary lockout devices (other than the lock).


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## varmit (Apr 19, 2009)

I was not attempting to argue either way on the relative safety of the installation. i was only trying to quote, what seems to be, the current applicable code(s). 

Yes, i may be wrong without knowing the "what ifs" of this particular installation, and as we all know - many codes are somewhat ambiguous and their interpretations vary dramatically from one jurisdiction to another.


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## Wiresmith (Feb 9, 2013)

varmit said:


> I was not attempting to argue either way on the relative safety of the installation. i was only trying to quote, what seems to be, the current applicable code(s).
> 
> Yes, i may be wrong without knowing the "what ifs" of this particular installation, and as we all know - many codes are somewhat ambiguous and their interpretations vary dramatically from one jurisdiction to another.



i wasn't taking what you were saying as argumentative, i think it is a good second look at what i came up with and i appreciate it.

just at the end of any code questions i always try to see what the real world problems are with doing things different ways. do you see any real world problems with the set-up? i'm honestly asking this question and not trying to be argumentative.

i'm still not seeing a likely scenario where he wouldn't be allowed to do what he is asking


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## frenchelectrican (Mar 15, 2007)

I am not sure excatally what code cycle the OP is from if he is from Oregon area I think they are on either '11 or '14 but I am not too amused if they did kicked to '17 by now.

I know there is other member he is from Oregon area and I hope he can chime in to comfirm what state of Oregon code saying on that part what OP posted. 

I know there were a extempted item but that is no longer legit after '99 or '02 but I have to look up the NEC to make sure I am reading the correct art numbers before I posted the correct info.


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## Wiresmith (Feb 9, 2013)

thinking about this thread, i thought of something a little abstract and it kind of applies to normal residential areas as well. i never asked the OP if there was concrete paths or parking lot connecting the two structures, that could actually be a parallel neutral path. he said he didn't have a parallel path but you really don't know until after energizing and checking neutral current at both places. i never thought about it before but reinforced concrete(driveways and sidewalks) could possibly serve as a decent parallel path in residences as well.


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## varmit (Apr 19, 2009)

Thanks! A good discussion helps to keep my old brain functioning.


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## colorado_electrician (Jun 11, 2018)

Wiresmith said:


> what about 250.32(B)(1) exceptions and 250.30(A)(1) exception 2


250.32(B)(1) Doesn't apply because the out building is being fed by a separately derived system (the transformer). 

250.30(A)(1) could apply and from reading through this post I agree that exception 2 would be the one we're looking at; therefore if the conditions are met no grounding conductor needs to be run to the remote building. 

Remote disconnect would be grounded and bonded.


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## Wiresmith (Feb 9, 2013)

colorado_electrician said:


> 250.32(B)(1) Doesn't apply because the out building is being fed by a separately derived system (the transformer).
> 
> 250.30(A)(1) could apply and from reading through this post I agree that exception 2 would be the one we're looking at; therefore if the conditions are met no grounding conductor needs to be run to the remote building.
> 
> Remote disconnect would be grounded and bonded.


i agree

post 19



Wiresmith said:


> i think 250.30(A)(1) via 250.32(B)(2)(b) actually might be more applicable to the OP's situation but i'm not for sure due to lack of details which i would only need to decide which code section allows it. i'm not seeing how its not allowed.


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