Bonding a trough

[Danruck]

Service conductors (4/0) enter an outdoor trough from the weatherhead. They are then tapped with #2 conductors to each of 2 - 100a meter cans and then terminate in a 100a main-breaker panel under each meter. The neutral lugs are bonded in the meter cans and the panels have main bonding screws. Steel nipples with threaded hubs are installed on top of each meter can and panel. The nipples enter the bottom of the trough and are provided with bonding locknuts. This appears to me as the entire installation is bonded together. My inspector disagrees. He says I still need a main bonding jumper from my trough enclosure to my neutral connection inside the trough. I assumed my trough was already bonded through the steel nipples using bonding locknuts. His request seems like its double bonding the trough. Please help me understand what Im missing. Thanks!

 

[infinity]

I agree with the inspector. The wireway should be bonded directly to the neutral not indirectly through the nipple.

 

[electrofelon]

And I disagree with the inspector, and as a consequence also Rob by the hypothetical syllogism rule. Since you have threaded hubs and bonding locknuts you meet 250.92(B) and the trough is bonded.

An alternative way to do it in the future is, since you need to tap the neutral conductor anyway, bolt a multi-port Lug or bar into the trough and you can split your neutrals there then the trough is definitely bonded.

 

[infinity]

The bonding jumper to the nipple is based on the #2 conductors in the raceway. The bonding jumper for the neutral is based on the size of the SEC's entering the wireway.

 

[LarryFine]

When I was a helper, my boss would have us drill or punch the right-sized hole in the bottom and use a split bolt with the nut on the outside of the trough, clamping the wire against the metal.

 

[augie47]

If I was making the call, I would consider it bonded but infinity makes a valid point.
Since there is some question it might be simplest top add a stud kerney on the neutral and remove all doubt.

 

[Danruck]

Maybe Im just over-thinking the entire issue. Its not a big deal to slap a lug on the trough and hit it with a bonding jumper. But why?? I can find no code reference to back up a decision either way. I agree its a roundabout way of doing the job but it just seems to me that all parts are already bonded by sheer mechanical contact.

 

[electrofelon]

Maybe Im just over-thinking the entire issue. Its not a big deal to slap a lug on the trough and hit it with a bonding jumper. But why?? I can find no code reference to back up a decision either way. I agree its a roundabout way of doing the job but it just seems to me that all parts are already bonded by sheer mechanical contact.

IMO 250.92(B) says clearly it is compliant as is.

 

[Eddie702]

I think it is compliant the way it is. Lets say it was done in rmc with only 1 meter socket and 1 panel with a tee feeding the meter socket and a LB feeding the panel would that not be compliant?

A raceway is a raceway

 

[infinity]

So looking at this in reverse, if the neutral is bonded in the trough then why do you need to install MBJ's in the service disconnects? The service disconnects are already bonded by the metal nipple and bonding jumper.

 

[electrofelon]

So looking at this in reverse, if the neutral is bonded in the trough then why do you need to install MBJ's in the service disconnects? The service disconnects are already bonded by the metal nipple and bonding jumper.

Because the NEC says so. But an interesting point and it doesn't make a lot of sense.

 

[Danruck]

Ha! Those were my exact words to the inspector.

 

[jaggedben]

... My inspector disagrees. He says I still need a main bonding jumper from my trough enclosure to my neutral connection inside the trough. I assumed my trough was already bonded through the steel nipples using bonding locknuts. His request seems like its double bonding the trough. Please help me understand what Im missing. Thanks!

If 'main bonding jumper' are his words that is evidence he doesn't know his code well enough.

If this were load side then you would need to bond the trough separately to your EGC, but I can't recall anything specifying that for the neutral in this situation.

If you do end up bonding it, I would probably just use a lay-in lug. While the kerney bolt suggestions above seem legit, I get a trying-too-hard vibe from them.

 

[electrofelon]

I would just bolt a big neutral bar right to the trough. You need to splice/tap the neutrals anyway. So kill every bird with one stone.

 

[jaggedben]

Yeah, I meant given that the splice is already done.

 

[electrofelon]

Big pet peeve of mine: I hate the bonding provisions (lack thereof actually) in most larger boxes and wireways. Often it's just a tiny screw and no anti-turn provision for the lug. There is bolting your own lug on but there is the paint which should be scraped off...but then I worry about corrosion/ different metals and usually put some deox on it.....just all seems hokey.

 

[Danruck]

Great feedback, guys. Thanks for the input.

 

[Eddie702]

Without doing anything xtra in the trough it is already double bonded in the meter socket and in the main panel(s).

 

[Danruck]

Thanks Eddie. My thoughts exactly!