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Help with Ground Bonding and Bushings

7303 Views 16 Replies 4 Participants Last post by  integlikewhoa
Need some help making sure I ground everything properly and in the past I have not used or known how and when to use a Ground bushing on conduit entering or exiting boxes.

This is for a solar install using micro inverters all 220v wiring.
Main panel (metal) with metal offset to a Shutoff/Disconnect switch (Also metal and I drilled holes in both boxes to make the connections no knockouts were used). Then there is metal conduit run to a PVC combiner box (Enphase Combiner box 3). From there metal conduit run up to roof into a Jbox.

I'm running 5 wires between these boxes.
2 hots, Neutral, 8g Thhn EGC ground and 6g Solid Bare Copper GEC ground.

in the picture the threaded HUB on top of the Disconnect is not installed yet. Didn't have it at the time of pic but that is a threaded hub connection.

My question is at any of these conduit connections do I need to use a ground bushing nut vs. a regular locking nut? Also which ground wire gets used? EGC or GEC?

I see the attached wiring diagram shows EGC gets bonded in the disconnect box (I'll strip back the coating and pass it threw the ground lug in the box already).

Does the Bare copper #6 GEC wire just pass threw the disconnect without any connections and what about the combiner box?
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You're also running EMT metal conduit, so you are triple grounded.
Here is how we would use a ground bushing in a PVC box. You need to both mechanically and electrically connect the metal casing of the cable together. In your case it is the conduit.

The bonding wire inside the cable is the bare copper while the green copper is used between the bonding bushings.

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So do I need to use a ground bushing anywhere in this setup?

I thought I read that if you drill your own conduit holes vs. using pre existing knockouts that might require a ground bushing?

I see in the PVC box above they used them on both sides of it. Do I need to use them in my combiner box which is PVC?
The general rule is you may use approved fittings made up properly on metal conduit to a metal enclosure to comply with it being grounded except when a connector enters a concentric knockout provision where any of the larger options are still available. The logic being that concentic KO's sacrifice some of the metal surface that is required for grounding. Ground bushing are then required in that instance so that a bond wire can connect from each conduit bond bushing to the metal cabinet. I see no requirement for bond jumpering when using either a hole saw, step bit or punched hole made by the electrician.

As for any plastic unclosures being supplied by metal conduits, bond bushing with a bonding wire running between all metal conduits is required.
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Another question.

I need to run 3/4" EMT on the roof down a wall underground over to the detached garage and back up the wall to the roof for the solar panels on the garage.

I'm running (2) number 10s and the two grounds #6 and #8.

Question is I don't want to run PVC 80 on the roof or down walls cuz of how it looks and expands but I'm afraid of running EMT underground. So I was thinking of using EMT down the walls and only PVC underground and stubbed up on both ends. My problem is how is bonding going to work on that? I really don't want to put boxes on each side where the transition is.

Whats the proper way to get from roof to roof?

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Teck90 is the perfect cable for that, but I don't know what it is in the USA. Actually I don't think it exists...

I would likely use a Female Adapter

If you look closely near the floor, you can see the transition in this picture

You will also likely need an expansion joint on each end so when the PVC conduit moves it does not rip your EMT out

I guess to finish the question, the EMT at both ends needs to be bonded, so you can use a bonding bushing for that also; at least in Canada you can.

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Thanks, I planned on using the thread adapters with the raintight for the EMT due to being outside.

I was more worried that they wanted a bonding bushing right where the PVC met the EMT like having to install a box. If they will let me do it only on one side of the EMT pipe I'll be ok.

Never used or seen PVC expansion joints. Home Depot doesn't even carry them. How long of a run before this is needed?
The PVC underground won't need the expansion joint, the temperature is pretty stable at 18" down.

Frankly I have never been able to run from one rooftop to another without getting more bends in the system than I could pull wire through easily, not to mention the NEC limit of four 90° bends (or equivalent wiggles). The j-boxes at the transition from wall to underground may become your best friend. Maybe your other friends will be LB's at the rooftop to redirect the run downward.

Use wire rated for wet location (thwn or thhn/thwn)... and in case you want to hedge your bet, stranded pulls easier on difficult runs.
And whatever you do, don't include any unnecessary 90° bends in the system, like below:


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And whatever you do, don't include any unnecessary 90° bends in the system, like below:
I agree with no unnecessary bends in a pull. That picture is from about 10 years ago and I can't remember why we did that; I think the equipment that was going to sit there (welder if I recall) would have sat in front of the quad so we just had to move it a bit to the side.

Also, in some cases depending on the entrance to the box / device, if you need to keep a specific orientation you many need a bend or a kick here and there, but they all add up.

Regarding the expansion joints, in our jurisdiction the inspectors want to see that expansion joint, not just because of frost heave, but just general ground movement; I would be surprised if the inspector did not want to see that as part of the transition from the EMT to PVC.

Plans failed today due to not showing a disconnect between the house and detached garage that Im trenching. Showed 225.31

Also plans didn't specify trenching or the depth showing as per table 300.5

So my question is on the Disconnect. It should be on the garage side right as the conduit is going up to the roof of the garage?

And my main solar disconnect needed to have an external handle to shut off. Does this also need that or is something like an A/C disconnect breaker or pull out ok? Fused or not fused? It will be a 10g 240v 20amp single circuit.

The NEC requires that the roof equipment must have an accessible disconnect in sight and no further then 50' away. Since this UG is strictly for the PV panels, I see no reason for any other disconnect... it's not like this is a service for the building. I'd submit it that way and clearly state that the disconnect was at the rooftop equipment location per NEC.
Currently there was not set to be anything but a Jbox on the garage roof. Are suggesting that instead of installing a disconnect on the ground level going up to the roof I just install it on the roof maybe instead of the jbox?
A disconnect is required on the roof by code... that's where the serviceman will be able to access it for safely disconnecting the equipment for service.

I see no reason or need or code requirement for any other disconnect. I can't speak for your inspector or plan checker but I would submit the plan showing the disconnect on the roof... I suspect it will get approved.
These are enphase micro inverters and have 240v ac out behind each panel. They are also rapid shutdown no 240v input they shut down at the panel. They don't require a disconnect on the roof and there is not one on the house roof. There is normally only one disconnect at the panel. But with a 2nd detached structure they seem to want a 2nd one on the detached garage per 225.31.
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