We installed RMC between a meter enclosure and a service disconnect using Myers Hubs (grounding type) for a 120/240V service. Our facility inspector insists that we need to install a small bonding jumper between the two myers hubs because we are utilizing concentric ko's. I feel that the RMC and the service neutral already provide the bond to metal parts and that the actual utility inspector will make us remove it. Am I missing something here? I'm reading 20.92(B), but I'm not really finding my answer.
Meter/Disco Bonding
- Thread starter quantum
- Start date
- Status
Buck Parrish
Senior Member
- Location
- NC & IN
Unless you're at the last cocentric knockout. He's right, you will need to utilize a bond like the facility inspector suggested. It will be easier to add a bonding jumper then it will to add grounding bushings. 250-92 (B) In the 2020 book
Last edited:
Buck Parrish
Senior Member
- Location
- NC & IN
Yes' It's required One way or the other. Because of the concentric knockouts.
What size conduit did you use? Most concentric knock outs go to 2.5 " maybe 3"
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Assuming your meter can has a factory bonded neutral (likely) and you have the neutral bonding screw in the main disco then you just need to bond one end of the nipple with a jumper sized per 250.102. Then the meter can, main disco. and the metallic nipple will be bonded per 250.92.
I'm am wondering why you are even using the Meyers hubs, though, with concentric KOs. Using a Meyers hub with concentric KOs is like having a screen door in a submarine.
Last edited:
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
He is wrong and this would serve no purpose. And you still would not be compliant with 250.92.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Since this is a service the concentrics have no impact as it has to be done per 250.92 regardless.
Buck Parrish
Senior Member
- Location
- NC & IN
Oh thats right. I'm wrong. Because the neutral is bonding the can. But what about the conduit? He might have sugested a grounding bushing.
We're industrial guys and that's what we have on hand. We only dress out a meter pole once every decade.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree the type of KO's do not matter, since this raceway contains service entrance conductors it requires bonding on one end with somthing other than a standard locknut.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
The nipple needs a bonding jumper on one end per my post #5.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Not that it matters but you only need the Myer's hub on the bottom enclosure. If there were no concentric or eccentric KO's on the bottom a bonding locknut on that side is all that's required.
The disconnect does not have concentric knockouts, so would that count as one end being bonded?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Yes but you would still need a bonding locknut as opposed to a standard locknut.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
As infinity mentioned you need more than a standard locknut to comply with 250.92. You mentioned that you are using a Myers hub that is of the grounding type (these are different that a standard Myers hub in that it has a lug on the locknut). You need to install a jumper from that lug to the enclosure or the neutral bar.
We installed the bonding jumper, but I still don't feel that it was necessary. Not to beat a dead horse, but this is a good code lesson for me. Am I reading 250.92(B)(2) wrong? That seems to indicate that a threaded hub, made up wrench-tight, was the only bond we needed.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The hub in that section is not for a Myers hub. A Myers hub is still held in place with a locknut. Now if it had a grounding locknut that might be a different story.
I'm trying to find this code reference, can you point me in that direction? (bonding on one end only)
As I recall it goes back to the listing (you would need the listing category and a UL White Book). Not all hubs are listed as an acceptable grounding means for service conductors. That is why the hub in your picture has the provision for bonding. Per the UL listing, a bond jumper would be required.
- Status