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WillK 05-31-2011 10:37 AM

8x8 junction box bonding
So I have this box as part of my feeder conduit run for my detatched garage sub-panel feeder:

I'm not certain that it is necessary because it is connected with metal conduit to the pipes outside which are themselves already bonded, but in order to avoid my inspector raising an issue since he seems to be big on metal things being bonded, I want to bond this box.

The problem is that the box does not have a 10-32 threaded hole for a grounding screw. Which is odd because the instructions reference a kit which is sold seperately to bond the cover to the box...

Anyway, am I correct in assuming that my only option is either drill and tap a 10-32 hole or drill a hole and attach a grounding screw by using a nut on the other side?

What the box does have is 4 holes for mounting, but they're 1/4" holes and my understanding is that whatever you attach ground with can only be used for ground (which also means if I bonded the cover, I'd need a new hole for that since I couldn't use a hole for bonding and cover attachment?)

gregzoll 05-31-2011 11:19 AM

If attached to metal conduit, and you connect the box the proper way, you are fine. As for you stating that the conduit is bonded, clarify.

WillK 05-31-2011 11:39 AM

Conduit grounding clamps at both ends. At the house, #4 solid copper wire passing through connecting to the ground bus bar on the main panel on one side and to the 2 ground rods on the other side. At the garage, #6 stranded copper wire passing through connecting to the ground bus bar on the subpanel and on to 2 ground rods on the other side.

If calling it bonded is incorrect use of the lingo, it is just a reflection of I find myself better able to understand what to do than how to describe it.

The conduit between the junction box and the service panel (on both ends) is PVC. The conduit between the junction boxes is rigid metal conduit.

jbfan 05-31-2011 11:48 AM

Since you used pvc, the you need to bond the metal box.
Drill and tap a 10/32 hole. Attach the bond wire to the box, and splice to the ground wire.

Or replace the metal box with a pvc box and forget the bonding.

WillK 05-31-2011 01:44 PM

I was going to say I don't actually have a ground wire in the junction box to splice to, but actually that's not precisely true...

So there are 3 conductors going through for the garage feeder, these are XHWN - this system is using the conduit as ground. This is for a 100A subpanel. These go straight through (enter through top, exit through back) with no splices. Same thing on both ends.

Also, I am running 3 THNN/THWN conductors for a 3-way switch. In the junction box, these splice to NM cable on both ends. The NM cables are of course going to have ground conductors to which I can splice (or for that matter I could put those directly under the ground screw I suppose)

The 3-way switch runs off a circuit in the garage. Bonding the garage junction box to the NM cable would give a ground path through the 3-way switch feeder.

In the house, the 3-way switch doesn't have its own path to ground, if it bonds to the junction box, it has a path through the conduit which connects to the ground bar of the main and garage subpanels.

Is this adequate... Or does a larger ground wire need to go to the J-box to cover the larger 1/0 cable for the 100A feeder? I think I have enough #4 ground wire to connect the junction box in the house to the main panel ground bus bar, this would tage a ground lug (which I have).

WillK 05-31-2011 01:48 PM

Let me just ask the question another way: If I just try to go the route of looking for the silver bullet and run a #4 solid copper wire to the junction box in the house, using a ground lug, and running #6 stranded to a ground lug in the junction box in the garage... Both connecting to their respective service panel ground bus bars. Is there any possibility that I am making a ground connection that is disallowed?

jbfan 05-31-2011 03:24 PM

I thought you used pvc.
You can not use the conduit as a ground unless you go from point a to point b with the rigid.
If you changed over to pvc along the way, you no longer have a conduit ground.

WillK 05-31-2011 03:42 PM


Originally Posted by jbfan (Post 658540)
I thought you used pvc.
You can not use the conduit as a ground unless you go from point a to point b with the rigid.
If you changed over to pvc along the way, you no longer have a conduit ground.

I thought that whether it was metal all the way from one panel to another, a ground clamp and ground conductor is required at each end... Being that I have that, I had assumed that the metal conduit from one ground clamp to the other was allowed as a ground conductor because the ground clamp provides better continuity than I'd ever get from EMT set screw connectors...

I only have a picture of one end, but this is basicly what I did on both ends of the underground conduit... This isn't good enough?

I want the correct info, but if I have to do something different, that's a problem because I don't have an easy way to pull more through the conduit, let alone money for either a ground conductor or for EMT conduit where I have PVC.

I went to PVC because the short run in the house was not a straight run... I had the materials for an EMT staight run, but I would've needed to spend more to get elbows and the money wasn't there so I returned the EMT to get the less expensive PVC.

If you're saying the ground clamps I have don't make it metal conduit from point A to point B, does grounding the metal junction boxes make the metal conduit that is continuous between them point A to point B?

WillK 05-31-2011 04:04 PM

Knowing that I tend to describe things in detail, and doing so I tend to end up with rambling wordy paragraphs that are hard to follow... And knowing that I might have been unclear... I made the block diagram below.

So given the way that the diagram is labelled, is not the conduit between B and C allowed to act as a ground conductor, and doesn't the copper wire from A to B and C to D connect that ground conductor making the ground connection from A to D?

WillK 05-31-2011 04:20 PM

1 Attachment(s)
This time I'll add the diagram. :whistling2:

Saturday Cowboy 05-31-2011 06:50 PM

if those 8x8 jboxes are attached to the metal pipe with metal lock nuts they are bonded. Pick up your tools and go home:)

WillK 05-31-2011 07:18 PM

Well, considering the inspector's request to put an insulating bushing where the load side SEU exits the meter socket, I used insulating bushings on the inside and metal lock nuts on the outside... But I think I might have 2 more metal lock nuts to put a metal lock nut on the inside under the insulating bushing.

Plus I have time to do that tommorrow due to the combination of 2 events: 1) the inspector has the day off so my inspection is Thursday, 2) I'm now unemployed. Although unemployment is a full time job if you do it right. But a little decompression time before starting the job search full time is good for the composure.

frenchelectrican 05-31-2011 10:53 PM

Are you using the new or exsting 2 inch ridge conduit ??

Second question for you is that the junction box is that the two inch conduits are line up for " straight " thru ? if that the case IMO that you got squeaked by with 8 by box normally I use 12 X 12 X 4 inch box for straight thru but use the big junction box for turn or offset then it will get bigger depending on which way I run it.


WillK 05-31-2011 11:03 PM

1 Attachment(s)
2" conduit is on the wall opposite the cover. It is oversized. Even the 1-1/2" PVC I'm using on the side wall is oversized. 1-1/4" would still meet conduit fill, but I had enough 1-1/2" PVC on hand that all I needed was the elbows.

The reason I mention it is 314.28 makes reference to an entrance opposite a cover being allowed based on the allowable bend radius for single conductors, which is why a 4" deep box can allow a 3-1/2" bend radius, and because a 1-1/4" conduit could have been used so 6x 1-1/4" is 7-1/2" thus an 8" box could be used with 1-1/4" conduit.

I'm attaching a photo of the garage feeder setup inside the house.

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