Metal junction grounding options

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Fred B

Fred B

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Upstate, NY
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Electrician
Needing to move several circuits of wireing due to new cutt-in of a dormer. Will install 2 metal enclosures to splice about 8 circuits and extend the wire around the new opening. How would you recommend bonding of these boxes? 1. Would you add a ground bus to land all the grounds from the NM? 2. Only use one circuit's EGC to bond the box? 3. Run a separate EGC from the enclosures back the panel supplying the circuits, sized to the largest ungrounded conductor? Or something else?

#1 would seem to ensure the enclosure remained bonded no mater what was to later change related to any individual circuit. #2 would be simple but if that circuit was to be disconnected the enclosure would no longer be bonded. #3 would accomplish same goal as #1 ensuring bonding no matter what changes occur to any individual circuit, but the practicality of doing this is a question mark. A single THHN ground would be easy enough to fish through but shouldn't it be in a conduit or flex for the entire run? Is there a MC single conductor cable that would work for #3? Have seen the single MC used as grounding conductor in past but always on very old installation nothing new.

A side thought as to requirements for AFCI. This modification, would that initiate inclusion of AFCI protection if it is not currently present? Seems it would.
 
I believe the rule is all the EGC's need to tie together and a bond needs made to the enclosure if a metallic enclosure.

installing a "ground bar" is usually the easiest way to do this unless there is only going to be maybe 4-6 conductors total involved in a splicing method.
 
You cannot run a single EGC back to the panel so #3 is out. That leaves #1 or #2. I would splice them all together and run a tail to the box. If you have more EGC's than a single wire-nut can handle them make two splices and pigtail them together.
 
Ground bar is easiest and cleanest if you have 8 circuits to extend. That is 16 EGCs to deal with. Eaton bars use a 10-32 screw and allow up to 3 egcs per hole if they are #10 or smaller and the same size. Wire nuts are inefficient because of the limit of 5 wires and you will need a jumper in each nut to interconnect the others.

Only other solution would be a giant Wago. Ive have seen 8 hole versions. Dont know if they make larger ones. And it would still need a pigtail to the box.
 
The problemn with a ground bar is that unless the bar is listed for the box all of the paint will need to be removed when it's screwed to the box. I'll stick with the splices. :)
 
Doesn't 250.8 allow this (ground bar screwed to the enclosure) without specific listing assuming the box came with a 10-32 screw? If the dimple where the 10-32 screw is painted, the metal should be thick enough to engage 2 threads.
 
Years ago, I had to interface twenty-four 12-2 MC cables with three 3/4" EMT home runs. I bought two generic 12-hole grounding bars and screwed them to the back of the junction box with self-threading machine screws.
 
suemarkp said:
Doesn't 250.8 allow this (ground bar screwed to the enclosure) without specific listing assuming the box came with a 10-32 screw? If the dimple where the 10-32 screw is painted, the metal should be thick enough to engage 2 threads.
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You would need to find something that meets the last part of the last sentence otherwise the bold applies.

250.96 Bonding Other Enclosures.
(A) General. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non–current-carrying parts that are to serve as equipment grounding conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where
necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any non-conductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or shall be connected by means of fittings designed so as to make such removal unnecessary.
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infinity said:
You would need to find something that meets the last part of the last sentence otherwise the bold applies.
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But the first sentence says "that are to serve as equipment grounding conductors." So if the screw that holds the ground bar to the enclosure is just serving to bond the enclosure, rather than to maintain continuity of the EGC, I would say 250.96(A) imposes no requirement.

Moreover, if the engagement of (2) threads is sufficient as per 250.8(A), then the non-conductive material would electrically only need to be removed from the threads. So I would find it reasonable to read "contact points and contact surfaces" in 250.96(A) to mean "the intentional contact surfaces that provide the bonding connection" rather than "any portions that happen to be in contact."

Cheers, Wayne
 
I wouldn't put too much thought into this. Two groups of four wirenutted and pigtailed together, one of the groups gets a pigtail to a ground screw in the box.

Move on to the next job.

-Hal
 
The contact points and surfaces are between the bar and the box. If there is paint it needs to be removed or the fitting needs to make the removal unnessary.

As I said earlier I agree with Hal just splice it.
 
infinity said:
The problemn with a ground bar is that unless the bar is listed for the box all of the paint will need to be removed when it's screwed to the box. I'll stick with the splices. :)
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True, I like to try to only purchase galvanized finish boxes, also mostly get boxes with no KO's. They never seem to have them in the desired places or for something like OP is doing will not be enough of them, will need reducers, etc. Easier to be able to put them wherever they work best for you.
 
kwired said:
I like to try to only purchase galvanized finish boxes, also mostly get boxes with no KO's. They never seem to have them in the desired places or for something like OP is doing will not be enough of them, will need reducers, etc. Easier to be able to put them wherever they work best for you.
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100% agree.

-Hal
 
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