"Re-grounding" Remote Building - Article 250.32

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Prior to 2008, it was acceptable to not install the equipment grounding conductor (E.G.C.) and rely on the grounded conductor (neutral) for fault return path if there is a short in the feeder. The neutral to ground bond would then occur in the remote panel. This method is still permitted in the 2014 Code so long as this is for existing applications and meets the three criteria listed. It seems like you are now being forced into including this E.G.C. from the source building and maintaining separation of neutral and ground in the remote building. My question pertains to the ability of any OCPD installed in the remote building to clear a fault when the building is located a great distance from the source. If you are no longer capable of excluding the E.G.C. and setting up this separate neutral to ground bond in the remote panel, this means the fault current would need to travel the E.G.C. back to the source circuit, through the main bonding jumper, then back through the neutral conductor to the remote building to clear the fault. This would be a great deal of line impedance that would reduce the short circuit current. The reduced short circuit current could potentially be below the pickup setting of the OCPD, not allowing it to trip. I don't see that the Code is permitting any special exemptions based on distance of a remote building from the source. It seems like this is creating an issue with the ability of these remote building OCPD to operate properly. Any thoughts on this issue? I can usually find answers by searching the forums for questions I have and have never really needed to make a new post. I have scoured the internet and Code forums and can't find any information about this distance between source and remote building question. All responses will be greatly appreciated!!
 

iwire

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Regardless of the bonding point the fault path is always all the way back to the source.

The only real difference is which conductors are carrying the fault current.
 

ActionDave

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I'm thinking that re-bonding the neutral at the second structure would make a branch circuit breaker trip faster.

Actually, no thinking at all. I'm forming the idea unencumbered by the thought process, but a shorter distance to the point where the neutral ground are bonded clearing a fault faster makes sense to me.
 

iwire

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I'm thinking that re-bonding the neutral at the second structure would make a branch circuit breaker trip faster.

Actually, no thinking at all. I'm forming the idea unencumbered by the thought process, but a shorter distance to the point where the neutral ground are bonded clearing a fault faster makes sense to me.

I once thought the very same thing as you and the OP until Don pointed out that the fault current still has to make to the transformer.

The only thing the location of the bond point changes is which conductor carries the fault current, the neutral or EGC.

Yes, in circuits over 30 amps the neutral is usually a larger conductor than the EGC so there will be a slight difference of impedance but in either case the conductors are large enough to trip the OCPD.

Or are you saying a code compliant EGC will not work? That will be bad news for things light site lighting or other long circuits. ;)
 

Sahib

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Location
India
The OCPD in the remote building would surely clear any short inside the building. The issue is short upstream to the OCPD. Since that usually happens outdoors, it may not be as hazardous or so the Code thinks.:)
 
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The change in EG size vs Neutral, as Iwire points out, is the current limiting factor. Make the EG full size and it shouldn't matter which path the fault current takes.

Bonding them together at both ends should make it even better. :angel:

Many years ago I did install feeders to fans on temporary grain storage (6 years is temporary) that when a bolted fault occurred it dropped out the coil voltage before any fuses blew. All three phases and EG shorted at the far end of the circuit. Total impedance from POCO transformers to fault was too high. Everything was designed for minimum, with exception that EGs were full sized, and it worked great until a maximum was thrown in the mix. Live and learn.
 

lauraj

Senior Member
Location
Portland, Oregon
In Oregon we are allowed to feed separate building without an EGC like old code used to allow. The main condition to do this however is there cannot be any other continuous metallic paths between the two buildings, because once we bond the neutral to the grounding conductor in the separate building, if there was say metal water pipe connecting the two buildings, that waterpipe would become a current carrying path for normal neutral current.

I've never looked up the ROP for when the code changed requiring an EGC with the feeder, but I wonder if it was done just to avoid the hazard of that neutral current being able to take other paths.
 

jumper

Senior Member
In Oregon we are allowed to feed separate building without an EGC like old code used to allow. The main condition to do this however is there cannot be any other continuous metallic paths between the two buildings, because once we bond the neutral to the grounding conductor in the separate building, if there was say metal water pipe connecting the two buildings, that waterpipe would become a current carrying path for normal neutral current.

I've never looked up the ROP for when the code changed requiring an EGC with the feeder, but I wonder if it was done just to avoid the hazard of that neutral current being able to take other paths.

The code change was the 2008 NEC.
 

iwire

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Location
Massachusetts
I've never looked up the ROP for when the code changed requiring an EGC with the feeder, but I wonder if it was done just to avoid the hazard of that neutral current being able to take other paths.

Well it was a proposal by Mike Holt and our moderator Ryan. No real reason other than bringing it more in line with all other NEC wiring.

I consider Ryan a friend but I disliked his proposal. :)
 

jaggedben

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Location
Northern California
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Solar and Energy Storage Installer
How many faults fall into the very small window of ohms where they would trip the breaker with the neutral but not the EGC? Probably a very small percentage. In the case of some feeders a neutral might not have been required to be bigger than an EGC so no difference at all. EGC sizing in the first place is based on what they think will trip the breaker when necessary, so there you go.
 

Sahib

Senior Member
Location
India
In other saner codes such as IEC, the maximum feeder/circuit length for a given OCPD is specified/calculated.
 
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