Two switchboards

[hhsting]

two neutral to ground bonds on one electrical system(the same transformer)at two separated areas connected by conductive paths, i think this is your real problem.

Dont follow. Neutral to bond are at service disconnects and 250.50 all grounding electrodes need to be bonded together in building. If GEC are installed per nec 2014 article 250.64(f)(3) with busbar in electric room outside of service equipment would that create objectionable current?

 

[Wire-Smith]

Dont follow. Neutral to bond are at service disconnects and 250.50 all grounding electrodes need to be bonded together in building. If GEC are installed per nec 2014 article 250.64(f)(3) with busbar in electric room outside of service equipment would that create objectionable current?

you have one transformer feeding two panelboards and both have a neutral to ground bond correct?

if so, everything grounded and bonded to both of those panels is effectively a parallel neutral and will carry part of the neutral current from either of the panelboards. its not a big deal if the panels are side by side, but in two separate areas, i see potential problems(sparking ground connections, shock hazards, etc.) and would red tag it if i was the ahj and would not do it if i was the contractor.

 

[hhsting]

you have one transformer feeding two panelboards and both have a neutral to ground bond correct?

if so, everything grounded and bonded to both of those panels is effectively a parallel neutral and will carry part of the neutral current from either of the panelboards. its not a big deal if the panels are side by side, but in two separate areas, i see potential problems(sparking ground connections, shock hazards, etc.) and would red tag it if i was the ahj and would not do it if i was the contractor.

You mean attached sketch cause objectionable current? If yes then how are the two service swbd grounded and bonded?

 

[Wire-Smith]

you could eliminate the problem several ways

1.) disconnect(s) before panelboards, if you use one then that's where your only main bond will be. if you use two, group the disconnects and those will be your only main bonds.

2.)group panelboards beside eachother

 

[hhsting]

you could eliminate the problem several ways

1.) disconnect(s) before panelboards, if you use one then that's where your only main bond will be. if you use two, group the disconnects and those will be your only main bonds.

2.)group panelboards beside eachother

How about attach sketch swbd#1 exterior wall fire pump room while swbd #2 inside fire pump room next to each other. Swbd #2 is for fire pump.

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[david]

Dont follow. Neutral to bond are at service disconnects and 250.50 all grounding electrodes need to be bonded together in building. If GEC are installed per nec 2014 article 250.64(f)(3) with busbar in electric room outside of service equipment would that create objectionable current?

As long as the bonding jumpers to building steel, water system, CEE, or any other electrode used to make up the grounding electrode system, sized for the largest service i do not see a violation

I do not think it matters if the Plate is in the area of service one or service two. By going to a boding plate with both services you have come as close as possible to a single point grounding electrode system as two service (laterals) will allow

IMO at least,

 

[Wire-Smith]

How about attach sketch swbd#1 exterior wall fire pump room while swbd #2 inside fire pump room next to each other. Swbd #2 is for fire pump.

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i would be comfortable with that, but would probably run a big bonding jumper from one panelboard to the other just for good measure and would personally still prefer one main disconnect(or two pretty much bolted together), although your illustration would be what i consider more inline with the more standard industry practice.

 

[Wire-Smith]

As long as the bonding jumpers to building steel, water system, CEE, or any other electrode used to make up the grounding electrode system, sized for the largest service i do not see a violation

I do not think it matters if the Plate is in the area of service one or service two. By going to a boding plate with both services you have come as close as possible to a single point grounding electrode system as two service (laterals) will allow

IMO at least,

wait until one of these days you run across a building with a double bond and you lose one of the service neutrals, you'll see things like flex sparking against conduits, pipes. and it could also happen without losing a neutral but would likely not cause a problem unless you have decent neutral current, but then again it doesn't take much current to do a lot of damage under the right circumstances. i have heard of people feeling circulating ground current in the shower (albeit metal plumbing, but you get the hint).

 

[hhsting]

i would be comfortable with that, but would probably run a big bonding jumper from one panelboard to the other just for good measure and would personally still prefer one main disconnect(or two pretty much bolted together), although your illustration would be what i consider more inline with the more standard industry practice.

I do have swbd #1 enclosure bonded and swbd #2 enclosure bonded together. See attach sketch. Would it still require bonding jumper in between?

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[Wire-Smith]

I do have swbd #1 enclosure bonded and swbd #2 enclosure bonded together. See attach sketch. Would it still require bonding jumper in between?

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i didn't say it required it, just that i would do it.

although i believe it is required in patient care areas if that happens to be the location. (if they serve patient care areas)(517.14)

 

[hhsting]

i didn't say it required it, just that i would do it.

although i believe it is required in patient care areas if that happens to be the location.

Its not patient care areas or healthcare. Its warehouse with office. Service equipment enclosure are typically bonded to the gnd bus, neutral bus with main bonding jumper. So swbd #1 and swbd #2 enclosure would be bonded together via common busbar, GEC system attached sketch post #29.

 

[david]

wait until one of these days you run across a building with a double bond and you lose one of the service neutrals, you'll see things like flex sparking against conduits, pipes. and it could also happen without losing a neutral but would likely not cause a problem unless you have decent neutral current, but then again it doesn't take much current to do a lot of damage under the right circumstances. i have heard of people feeling circulating ground current in the shower (albeit metal plumbing, but you get the hint).

What do you do when the fire pump service is required to be remote from other service disconnects?


I still do not see what you are pointing to as a code violation, what if one service was single phase and one service three phase taken from the same three phase utility bank, happens a lot around here.

 

[Wire-Smith]

What do you do when the fire pump service is required to be remote from other service disconnects?

i can't think of a scenario where you can't get rid of objectionable current, if you would like to expand on what you are describing i would appreciate it. sometimes the easiest way is to add an additional transformer at the premises for the "normal electrical system", sometimes it's easier to add disconnects to where all the main bonds are grouped.

I still do not see what you are pointing to as a code violation, what if one service was single phase and one service three phase taken from the same three phase utility bank, happens a lot around here.

this is what i see as the likely code violation

250.6 Objectionable Current. (A) Arrangement to Prevent Objectionable Current. The grounding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally non–current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable current

in the O.P.s scenario with two main bonds in different areas(not very close to each-other) served by the same transformer you would have neutral current on your grounded equipment if you have any neutral load, your grounded equipment is a parallel neutral path.

 

[hhsting]

i can't think of a scenario where you can't get rid of objectionable current, if you would like to expand on what you are describing i would appreciate it. sometimes the easiest way is to add an additional transformer at the premises for the "normal electrical system", sometimes it's easier to add disconnects to where all the main bonds are grouped.





this is what i see as the likely code violation


in the O.P.s scenario with two main bonds in different areas(not very close to each-other) served by the same transformer you would have neutral current on your grounded equipment if you have any neutral load, your grounded equipment is a parallel neutral path.

Utility in our area will only serve with one transformer not two. What do you mean by disconnects where main bonding jumpers are grouped?

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[hhsting]

i can't think of a scenario where you can't get rid of objectionable current, if you would like to expand on what you are describing i would appreciate it. sometimes the easiest way is to add an additional transformer at the premises for the "normal electrical system", sometimes it's easier to add disconnects to where all the main bonds are grouped.





this is what i see as the likely code violation


in the O.P.s scenario with two main bonds in different areas(not very close to each-other) served by the same transformer you would have neutral current on your grounded equipment if you have any neutral load, your grounded equipment is a parallel neutral path.

Even when service discos grouped you have parallel paths. Resistance of cable would be almost same so current divide between two paths but paths are still there.

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[Wire-Smith]

Utility in our area will only serve with one transformer not two. What do you mean by disconnects where main bonding jumpers are grouped?

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The additional transformer would be on the premises side of the service, so you can do your main bond for that system at and only at the transformer.

I mean having the main disconnects grouped where the only main bonds on the premises are. You would still technically have circulating ground current because of two bonds, but it would arguably and likely not be objectionable current because they are physically located and connected so closely together. Its like on commercial buildings with multiple units and you have multiple main disconnects grouped together with multiple main bonds, although you could do it a better way I don't see a likely problem since they are grouped.

 

[Wire-Smith]

Even when service discos grouped you have parallel paths. Resistance of cable would be almost same so current divide between two paths but paths are still there.

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My concern is not the neutral current dividing among the two service neutrals, it would do that.

My concern is the bonded and grounded equipment, like conduits, grounding electrode conductors, equipment grounding conductors, these would be carrying neutral current if two main bonds from one transformer are located in different areas and bonded by things such as building steel, grounds, pipes, reinforced concrete, etc, or a combination of them

 

[hhsting]

My concern is not the neutral current dividing among the two service neutrals, it would do that.

My concern is the bonded and grounded equipment, like conduits, grounding electrode conductors, equipment grounding conductors, these would be carrying neutral current if two main bonds from one transformer are located in different areas and bonded by things such as building steel, grounds, pipes, reinforced concrete, etc, or a combination of them

I meant that what you are saying is neutral current going to GEC, GE it would still do that even if service disconnects are grouped closely. The neutral parallel path would still be there.

 

[hhsting]

The additional transformer would be on the premises side of the service, so you can do your main bond for that system at and only at the transformer.

I mean having the main disconnects grouped where the only main bonds on the premises are. You would still technically have circulating ground current because of two bonds, but it would arguably and likely not be objectionable current because they are physically located and connected so closely together. Its like on commercial buildings with multiple units and you have multiple main disconnects grouped together with multiple main bonds, although you could do it a better way I don't see a likely problem since they are grouped.

I think utility around here do give another transformer if for fire pump and thats my case.

So what if you have two separate utiltiy transformers? Would this still happen?

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[Wire-Smith]

I meant that what you are saying is neutral current going to GEC, GE it would still do that even if service disconnects are grouped closely. The neutral parallel path would still be there.

Correct it would, but since they are so closely grouped it's not much different then say you have a parallel feed(not talking about your scenario, one service but parallel wires for ampacity. So say you have two parallel service neutrals going to one main switchboard or whatever, and the neutrals land on the neutral bar, say it's a decent size piece of equipment and the neutrals are a foot apart on the neutral bar, and it's old school and both mounting bolts bond it to enclosure. Do you think much neutral current is going to be on the related grounded and bonded non current carrying equipment? It would be negligible if anything, that is effectively the same thing you are doing with keeping them close together and bonding the enclosures right there close to the main bonds. Current discriminates, it will take all paths but disproportionately relative to impedance, shorter path=lower impedance.