parallel path/objectionable current

[electrofelon]

Multi-part question here:

1. When installing a service, do you try to set things up so that there is only one neutral-ground bond to avoid a metallic raceway carrying neutral current? Of course this may not be possible with equipment that has a factory neutral to case bond like most meters and some CT cabinets, but say you have a pull box, buss gutter, or trough on a service; would you keep the neutral unbonded and run a bonding jumper back to the service disconnect or use a nonmetallic raceway between them?

2. Have you ever been cited by an inspector for 250.6 for creating a parallel path at a service?

3. The NEC is very specific that a SDS shall have only one bond point (unless the interconnecting raceway is nonmetallic). Why dont they specify the same thing with services? As mentioned, of course this would cause some problems with some meters and CT cabinets, but a non-metallic raceway could be used or the NEC could just say they cant be bonded - they certainly haven't shied away from making manufacturers design equipment a certain way in the past.....Why is an SDS different?

 

[GoldDigger]

Multi-part question here:

1. When installing a service, do you try to set things up so that there is only one neutral-ground bond to avoid a metallic raceway carrying neutral current? Of course this may not be possible with equipment that has a factory neutral to case bond like most meters and some CT cabinets, but say you have a pull box, buss gutter, or trough on a service; would you keep the neutral unbonded and run a bonding jumper back to the service disconnect or use a nonmetallic raceway between them?

2. Have you ever been cited by an inspector for 250.6 for creating a parallel path at a service?

3. The NEC is very specific that a SDS shall have only one bond point (unless the interconnecting raceway is nonmetallic). Why dont they specify the same thing with services? As mentioned, of course this would cause some problems with some meters and CT cabinets, but a non-metallic raceway could be used or the NEC could just say they cant be bonded - they certainly haven't shied away from making manufacturers design equipment a certain way in the past.....Why is an SDS different?

Actually the NEC does prohibit creating parallel paths after the service disconnect. What happens on the POCO side of the demarcation point, whether you are installing the equipment or they are, is still not governed by NEC.
If there is a ground neutral bond inside the meter enclosure and there is an NEC-acceptable EGC (wire or raceway) coming from the meter enclosure to your main panel, then you are not required to add an additional bonding jumper in the panel. But if you do, it can still fall within the nebulous sphere of the POCO side of the service point.
With an SDS you control the whole thing and the whole thing is subject to NEC rules. An SDS is not a service.

 

[electrofelon]

Actually the NEC does prohibit creating parallel paths after the service disconnect. What happens on the POCO side of the demarcation point, whether you are installing the equipment or they are, is still not governed by NEC.
If there is a ground neutral bond inside the meter enclosure and there is an NEC-acceptable EGC (wire or raceway) coming from the meter enclosure to your main panel, then you are not required to add an additional bonding jumper in the panel. But if you do, it can still fall within the nebulous sphere of the POCO side of the service point.
With an SDS you control the whole thing and the whole thing is subject to NEC rules. An SDS is not a service.

thanks for the reply. Lets clear a few things up just to make sure we are on the same page. Lets call them bonding jumpers on the line side of the disconnect (seeing EGC when talking about services makes my brain crash. Lets talk about a meter only piped to a separate service disconnect. Lets call the service point at the weather head. Given these conditions, and lets say also there is a pull box between the meter and the disco and all the pipe is EMT. You have two options: you could have a neutral terminal bar in the pull box properly bonded to the box and land the neutral(s) there, or you could have the neutrals run straight through unbonded and run a bonding jumper back that box to bond it. A) which would you do B) why doesnt the NEC prohibit parallel paths at the service like they do after the service disconnect and on SDS's? C) if you do the neutral bond method for the pull box and are cited for 250.6 what do you say?

 

[GoldDigger]

thanks for the reply. Lets clear a few things up just to make sure we are on the same page. Lets call them bonding jumpers on the line side of the disconnect (seeing EGC when talking about services makes my brain crash. Lets talk about a meter only piped to a separate service disconnect. Lets call the service point at the weather head. Given these conditions, and lets say also there is a pull box between the meter and the disco and all the pipe is EMT. You have two options: you could have a neutral terminal bar in the pull box properly bonded to the box and land the neutral(s) there, or you could have the neutrals run straight through unbonded and run a bonding jumper back that box to bond it. A) which would you do B) why doesnt the NEC prohibit parallel paths at the service like they do after the service disconnect and on SDS's? C) if you do the neutral bond method for the pull box and are cited for 250.6 what do you say?

Let me take a.stab at B first:
1. The POCO side of the service disconnect is by design a multiply grounded system. There is a ground at the secondary of the transformer, which may supply several services, each of which will be independently grounded. The secondary neutral may run from one transformer to the next and be grounded at each.
(The ground needs to be maintained even if all of the service neutrals are disconnected.
The primary neutral is deliberately even more multiply grounded, and at that voltage the earth connection can actually be a fault clearing path.
2. NEC has no jurisdiction over POCO wiring.

 

[electrofelon]

Let me take a.stab at B first:
1. The POCO side of the service disconnect is by design a multiply grounded system. There is a ground at the secondary of the transformer, which may supply several services, each of which will be independently grounded. The secondary neutral may run from one transformer to the next and be grounded at each.
(The ground needs to be maintained even if all of the service neutrals are disconnected.
The primary neutral is deliberately even more multiply grounded, and at that voltage the earth connection can actually be a fault clearing path.
2. NEC has no jurisdiction over POCO wiring.

I dont buy that response. I mean yes all true, however "the service" generally consists of a bunch of stuff between the service point and service disconnect that is customer owned equipment. Why is the NEC like, "ahh, forget it, wel'l just start worrying about neutral current on raceways after the service disconnect"?

 

[mwm1752]

I am trying to visualize both of your statements
sounds like you have a meter where the grounded conductor is bonded to the metal housing -- meter is part of an overhead service drop -- you have a jbox in between the service disconnect and meter containing unfused wiring -- all raceways are metal from service drop to service disconnect -- no clue on service size but since their is a simple meter housing I am assuming 200 Amp.

Electrode conductor should tie to meter housing -- grounded conductor floats after meter connection never to come in contact with metal housings -- accessibility to electrode conductor attachment in meter.

 

[david]

Multi-part question here:

1. When installing a service, do you try to set things up so that there is only one neutral-ground bond to avoid a metallic raceway carrying neutral current? Of course this may not be possible with equipment that has a factory neutral to case bond like most meters and some CT cabinets, but say you have a pull box, buss gutter, or trough on a service; would you keep the neutral unbonded and run a bonding jumper back to the service disconnect or use a nonmetallic raceway between them?

2. Have you ever been cited by an inspector for 250.6 for creating a parallel path at a service?

3. The NEC is very specific that a SDS shall have only one bond point (unless the interconnecting raceway is nonmetallic). Why dont they specify the same thing with services? As mentioned, of course this would cause some problems with some meters and CT cabinets, but a non-metallic raceway could be used or the NEC could just say they cant be bonded - they certainly haven't shied away from making manufacturers design equipment a certain way in the past.....Why is an SDS different?

I do not see anything wrong with the way you laid out your design.

Yes you should take in account objectionable currents when laying out your service.

All the metal needs to be bonded to the service grounded conductor. And installing a main bonding jumper from the (neutral) at the service disconnect back to a CT cabinet or a junction box would help eliminate a path for objectionable current.

 

[GoldDigger]

All the metal needs to be bonded to the service grounded conductor. And installing a main bonding jumper from the (neutral) at the service disconnect back to a CT cabinet or a junction box would help eliminate a path for objectionable current.

Adding an additional path or lowering the resistance of the preferred path cannot eliminate objectionable current on the other paths. It can simply reduce its magnitude to the point where it might not be as objectionable in practice.
I do not think that the NEC defines "objectionable", so as long as nobody objects....

 

[electrofelon]

Adding an additional path or lowering the resistance of the preferred path cannot eliminate objectionable current on the other paths. It can simply reduce its magnitude to the point where it might not be as objectionable in practice.

Well it would eliminate the parallel path if the neutral was not bonded at the CT cabinet or pull box. It is code compliant to either bond the neutral right there at the ct or pull box, or not bond it directly with the neutral and run a bonding jumper from the main. With the latter there would be no parallel path. It would be just like the way a sds is set up when the bond is at the first disconnecting means. In this scenario i am ignoring equipment that is factory bonded and/or "unbondable"

I am trying to visualize both of your statements
sounds like you have a meter where the grounded conductor is bonded to the metal housing -- meter is part of an overhead service drop -- you have a jbox in between the service disconnect and meter containing unfused wiring -- all raceways are metal from service drop to service disconnect -- no clue on service size but since their is a simple meter housing I am assuming 200 Amp.

Electrode conductor should tie to meter housing -- grounded conductor floats after meter connection never to come in contact with metal housings -- accessibility to electrode conductor attachment in meter.

just to be clear this is an academic question. I dont really care where the GEC attaches. The way you have it laid out is sort of a bad example of what I am trying to say because the meter is probably unbondable, but if it was, then you could hit it with a bonding jumper (instead of attached the neutral to it there) and eliminate the parallel path. Its all about having only one neutral ground bond point like is required for SDS's.

 

[ActionDave]

..... Why is the NEC like, "ahh, forget it, wel'l just start worrying about neutral current on raceways after the service disconnect"?

While not very technical that sums up the NEC position quit well. Don't fight it, just assimilate and you'll feel better.

 

[mwm1752]

just to be clear this is an academic question. I dont really care where the GEC attaches. The way you have it laid out is sort of a bad example of what I am trying to say because the meter is probably unbondable, but if it was, then you could hit it with a bonding jumper (instead of attached the neutral to it there) and eliminate the parallel path. Its all about having only one neutral ground bond point like is required for SDS's.[/QUOTE]


I glad its clear now & you don't care -- seems like any answer that doesn't fit your vague hypothetical question is good reason dislike. good job

 

[ronaldrc]

Multi-part question here:

1. When installing a service, do you try to set things up so that there is only one neutral-ground bond to avoid a metallic raceway carrying neutral current? Of course this may not be possible with equipment that has a factory neutral to case bond like most meters and some CT cabinets, but say you have a pull box, buss gutter, or trough on a service; would you keep the neutral unbonded and run a bonding jumper back to the service disconnect or use a nonmetallic raceway between them?

2. Have you ever been cited by an inspector for 250.6 for creating a parallel path at a service?

3. The NEC is very specific that a SDS shall have only one bond point (unless the interconnecting raceway is nonmetallic). Why dont they specify the same thing with services? As mentioned, of course this would cause some problems with some meters and CT cabinets, but a non-metallic raceway could be used or the NEC could just say they cant be bonded - they certainly haven't shied away from making manufacturers design equipment a certain way in the past.....Why is an SDS different?

First question, Yes I think most Electricians do but its hard to do when your meterbase neutral is bonded
directly to the can and you have to bond the main service neutral to the service can enclosure.

But in this tri state area of Tn,Va and NC all the inspectors have always excepted this setup without question
and look the other way.

Second and 3rd question, Could be but I don't know this for sure ,the CMP might except this setup at the main because it
does not pose an electrical shock hazard as it does on the customers user end of the branch circuits.

Like jumping the neutral and ground of a clothes washer or changing it to a two wire circuit, in this case if you
loose your neutral connection and have metal water lines the pipe will become your only neutral return back to
your panel feeding this washer, making it a very dangerous shock hazard if your washer is turned on and you
are touching the washer and pipe at the same time you could recieve a fatal shock.

Ronald

 

[electrofelon]

I glad its clear now & you don't care -- seems like any answer that doesn't fit your vague hypothetical question is good reason dislike. good job

Sorry if I offended you, that was not my intent. I dont care about where the GEC attaches because I was talking about multiple neutral/ground bonds and parallel paths which doesnt involve system grounding or equipment earthing. I just didnt want superfluous information to cloud the discussion.

 

[mbrooke]

Kinda off topic but I know this, California's Utilities and some European ones got it right. The rest have no business when it comes to grounding and bonding.

But to answer the original I try to reduce objectionable currents as much as I can even if it means bending the NEC rules:roll: