Bonding neutral and ground at service end box in NYC

[LarryFine]

Hold on a second... How and why are they accepted on services if there is objectional current? isn't objectional current forbidden by code?

One the line side of the main disco, the neutral and any metallic enclosures and raceways are considered to be the same conductor.

 

[Tainted]

So based on our conversations is this how it's supposed to be bonded and grounded (see picture below)? Do I need a GEC from the service end box to ground bus or just between the service switch and ground bus?

 

[augie47]

IMO what you have drawn is compliant

 

[Tainted]

IMO what you have drawn is compliant

What I still don't get is why do we need to bond neutral and service end box if we already have the neutral bonded to the service switch?

If there is a fault at the service end box, there is still a path to clear the fault

 

[infinity]

If there is a fault at the service end box, there is still a path to clear the fault

Yes it's bonded to the neutral so a fault will return to the source via the neutral conductor. Without the bond it's possible that a metal part could be energized and no one would know.

 

[augie47]

If I'm not mistaken you could choose to bond it with a bonding jumper back to the panel....bonding to the neutral seems easier

 

[electrofelon]

IMO what you have drawn is compliant

What I still don't get is why do we need to bond neutral and service end box if we already have the neutral bonded to the service switch?

If there is a fault at the service end box, there is still a path to clear the fault

I would remove the bond between the two boxes. IT serves no purpose and is a parallel path.

 

[Tainted]

Yes it's bonded to the neutral so a fault will return to the source via the neutral conductor. Without the bond it's possible that a metal part could be energized and no one would know.

No my point is, wouldn't bonding the neutral to the service end box enclosure be pointless and redundant since we're already bonding the neutral to the service switch enclosure? See edited diagram below, I removed the bonding of the service end box neutral to service end box enclosure. Red x shows the fault and red line shows the path back to neutral source.

 

[electrofelon]

No my point is, wouldn't bonding the neutral to the service end box enclosure be pointless and redundant since we're already bonding the neutral to the service switch enclosure? See edited diagram below, I removed the bonding of the service end box neutral to service end box enclosure. Red x shows the fault and red line shows the path back to neutral source.
View attachment 2569842

Yes, post #22 you had an extra un-needed path. There are several ways to set it up. Either bonding it directly to the neutral (in the same enclosure) or you can run a jumper to the neutral somewhere else (which is what you have in the revised drawing.

 

[Tainted]

Yes, post #22 you had an extra un-needed path. There are several ways to set it up. Either bonding it directly to the neutral (in the same enclosure) or you can run a jumper to the neutral somewhere else (which is what you have in the revised drawing.

Ah I see makes sense. So it's probably more economical to do it post #22 without the the un-needed path. Any advantages or disadvantages?

Edit: wait.. I just realized service end box does not have a fuse, so I don't think this will clear the fault in post #28 lol

 

[electrofelon]

Ah I see makes sense. So it's probably more economical to do it post #22 without the the un-needed path. Any advantages or disadvantages?

Edit: wait.. I just realized service end box does not have a fuse, so I don't think this will clear the fault in post #28 lol

Bonding with jumpers back to a central point would have the advantage of avoiding neutral current flowing on the raceways (removing the N-case bond in post 22).

Well we are always at the mercy of the POCO's fusing for anything ahead of the service OCPD, its doesnt matter how you bond.

 

[LarryFine]

So based on our conversations is this how it's supposed to be bonded and grounded (see picture below)? Do I need a GEC from the service end box to ground bus or just between the service switch and ground bus?

View attachment 2569839

I would say the EGC as a conductor should be omitted; as a conduit, it's acceptable.

 

[jaggedben]

I would remove the bond between the two boxes. IT serves no purpose and is a parallel path.

If that represents a green wire, I agree. If it represents a metallic conduit, it's okay.

...

Edit: wait.. I just realized service end box does not have a fuse, so I don't think this will clear the fault in post #28 lol

It may or may not trip a circuit breaker or fuse on the utility network. Even if it doesn't, it's likely to get noticed if it's bonded. Whereas if it's not bonded it will just sit there waiting to electrocute the next person who touches it. Bit of a trade off perhaps but the code has made a clear choice.

 

[Provision&installation]

I have what I believe is a similar situation and I was actually going to post a new thread about it, but I'll go ahead and ask here. Hope this does not constitute a thread-jack.

This box is the utility hand-off point to the customer. From this box the parallel feeds go in the building to a main meter gear, which I believe is the point where the neutral bonding jumper is. I'm trying to wrap my head around it, and I'm not seeing any objectionable current simply because the neutral is not bonded in this box, so everything still has to run through neutral conductors to get back to the transformer, but for some reason my feelz make me want to believe that the neutral bonding jumper should be in this hand-off box, I suppose just because it's the closest connection point to the transformer.

https://imgur.com/QzlnSLc

 

[jaggedben]

If that box is subject to the NEC* then the NEC requires the box to be bonded to the neutral. See 250.92(B)(1). This is not a "neutral bonding jumper" and is not your main neutral-to-ground connection! It is just bonding the box!

The main neutral to ground bond(s) are called a "Main Bonding Jumper" and are always (repeat, always) at the service disconnect(s). I use the plural because if you have multiple service disconnects you have an MBJ in each one. I repeat: A service disconnecting means enclosure, however many there are, will have a Main Bonding Jumper that connects the grounded conductor (usually a neutral) to the enclosure and to the equipment grounds for the feeders and branch circuits. See 250.24(B).

The NEC requires that metal conduits on the supply side of the service disconnect act as parallel paths for neutral current where they run between boxes which (like the one in your picture) don't have listed threaded hubs. Again, see See 250.92(B). That's right, it requires it. It requires a box like that on the supply side of the service disconnect to be bonded to the neutral, and then it requires the box with the service disconnect to also be bonded to neutral.

*We could possibly split hairs over whether the NEC rules apply to box in your pic if that is the location of the service point. But there are plenty of such boxes - such as almost every stand alone meter socket on a residential service - to which the NEC definitely applies. These boxes are all bonded to the neutral, and the pipe from the meter socket to the service panel is a parallel path. This is required by the NEC.

As mentioned above, objectionable current isn't defined in the NEC. So I (and many others) have always taken it to mean something like "Current that runs on something other than the intended circuit conductors, unless caused by something the NEC explicitly requires or permits." Current running on metal conduit on the supply side (not the load side!) of the service disconnecting means is one of those things the NEC explicitly permits or even requires. Another situation in which the NEC explicitly permits parallel paths is GEC taps for multiple service disconnecting means. See 250.64(D)(1) or (2). Generally the NEC does not permit parallel paths on the load side of the service but permits it at the service or on the supply side.

Everything I've said so far is about bonding. The OP on this thread at least partly conflated this with grounding (i.e. the grounding electrode conductor (GEC) connection point. They aren't the same thing. You always have a main bonding jumper in the service disconnect(s). You may be required to bond other stuff to neutral on the supply side. You may ground your service (the GEC) at the service disconnect, or on the supply side. They are not the same thing and don't have to be at the same place.

 

[texie]

Wow, this is a wildly misunderstood area by many, including inspectors. First off, all services fed from a grounded POCO supply must have a MBJ at the service disconnect(s), regardless of the wiring methods used. Any metallic items ahead of the service disconnect must be bonded in a manner compliant with 250.92. This is usually done by bonding the grounded conductor to the enclosure but there are other options as well.
Over the years I have seen way to many metallic items ahead of the service disconnect not bonded at all due to PVC raceways or not in a compliant manner. This is often at a CT cabinet that has PVC as the connection raceways. Then the argument usually goes, well, "not my problem as it belongs to the POCO". This is simply not true. Even if you make the case that the NEC does not apply for this reason, the NESC, which the POCO must follow, requires all metallic items to be properly bonded as well. Another common bonding issue I see are metallic service raceways(s) run down a POCO pole that transitions to PVC at grade. Way to often that metallic raceway is left unbonded and could be deadly to anyone who touches it.
These kinds of errors can lead to deadly consequences just lying in wait, sometimes for decades.

 

[wwhitney]

If that box is subject to the NEC* then the NEC requires the box to be bonded to the neutral. See 250.92(B)(1).

So, that is what I had understood, that the box would have to be bonded to the neutral service conductor right there in the box, until this thread came up and I reread 250.92.

250.92(A) basically says all the non-current carrying metal parts of the service disconnect and upstream have to be bonded together. Then 250.92(B) gives you various way to do that bonding, of which 250.92(B)(1) is bonding equipment to the grounded service conductor, but that is not the only option.

So say your service point is in a "service end box", and from it you have a regular KO, a length of RMC, and a service disconnect enclosure, again with a regular KO. Your two enclosures and the length of RMC all need to be bonded together per 250.92(A).

The MBJ bonds the service disconnect enclosure to the grounded service conductor, so that takes care of the first of the three items. Two regular locknuts does not suffice to bond the RMC to an enclosure under 250.92(B), so you use a bonding type locknut on the service disconnect end, as per 250.92(B)(4). That takes care of the RMC.

Which leaves just the question of how to bond the service end box. You could bond it directly to the grounded service conductor per 250.92(B)(1), and then just use two regular locknuts on the RMC entry. That method will give you parallel grounded conductor current on the RMC conduit, because the two locknuts, properly installed, will bond the box, just not in the manner required by 250.92(B).

Or you could decide to bond the service end box to the already bonded RMC conduit, via another bonding type locknut as per 250.92(B)(4). That lets you omit any direct connection of the grounded service conductor to the service end box within the service end box itself, avoiding parallel paths for grounded conductor current.

Cheers, Wayne

 

[wwhitney]

avoiding parallel paths for grounded conductor current.

Well, that assumes that the service lateral itself is not in a metallic wiring method. If it is, and if that wiring method is bonded to the grounded service conductor on the utility side of the service point, and if that that wiring method is also bonded to the service end box, then you would still have a parallel path for grounded conductor current.

The only way to avoid that would be to use a non-metallic method between the service end box and the service disconnect, which would then require you bond the service end box to the grounded service conductor. Then you avoid any NEC-side parallel paths, although the service lateral itself will have a parallel path.

Cheers, Wayne

 

[jaggedben]

Wayne that was rather a lot of words to point out a tiny exception that makes what I said 99% instead of 100% true. Okay bonding locknuts and everything else just right and then no parallel path, perhaps.

Why do no code-knowledgeable professionals go to the trouble of always using bonding lucknuts to avoid parallel paths on service raceways and enclosures? Because 250.80, 250.92 and 250.142 all permit you to use the grounded conductor to bond there. And the bonding is required.

 

[LarryFine]

The neutral at the service establishes the zero-volts reference for the premises.

Everything metallic ahead of that point is part of the service neutral conductor.

That's why the neutral can be bare. Same being able to touch the meter base.