When to require bonding both ends of a home-run conduit to the EGC?

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photonboy

Member
Location
Berkeley, CA, USA
Occupation
Ex roof monkey, current desk jockey
The only code section I can find that specifically discusses bonding a metal raceway on both ends is 250.64(E) and that seems to only refer to the GEC from a main panel to the Earth.

The scenario we encounter every day is a roof j-box with EMT or metallic flex as the home run. Sometimes these can be long runs, over multiple roof planes, many couplings/conduit bodies before arriving at the combiner or inverter down below.

We have been asking for these longer runs to be bonded on both ends, in the inverter or combiner AND inside the j-box..

We have been getting pushback saying that bonding on only one end is sufficient. My thinking, and my experience, is that some of those conduit connections along the way can be loose (I used to find couplings that the installer forgot to tighten A LOT when doing O&M) and this can compromise the bonding, potentially leaving one side of a run improperly bonded in case of a fault. This can get someone hurt or killed.

Wanted to get the thoughts on this subject from other experienced installers, O&M techs and even any inspectors who might be on the forum.

Thanks.
 
photonboy said:
The scenario we encounter every day is a roof j-box with EMT or metallic flex as the home run. Sometimes these can be long runs, over multiple roof planes, many couplings/conduit bodies before arriving at the combiner or inverter down below.

We have been asking for these longer runs to be bonded on both ends, in the inverter or combiner AND inside the j-box..
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Bonded in what way? What cases are you concerned about: is the combiner/inverter enclosure metallic or non-metallic; is the roof j-box metallic or non-metallic; does the metallic raceway qualify as an EGC (any FMC in the run would need to comply with 250.118(6)); and does the metallic raceway contain a wire-type EGC?

For the case where a wire-type EGC is contained in the metallic raceway, if at least one enclosure is non-metallic, then bonding the raceway at one end suffices. If both enclosures are metallic, then the bonding required by 250.148 will have the effect of bonding the raceway to the wire-type EGC at each end.

Cheers, Wayne
 
I should have clarified that I meant that we would like a bonding bushing on each end of longer metallic conduit runs, each end with a lug that has the EGC bonded to it. The concern is that in the case of a loose fitting somewhere in the run that might compromise the raceway bonding continuity we are still safe since the other end of that break in the continuity is also bonded. The only code section I've found that calls for bonding both ends of the raceway is 250.64(E) which only relates to GEC to Earth runs. Our thinking is that the NEC is a minimum standard and does not account for all scenarios, so we are erring on the side of being safer. Unfortunately some installers are pushing back and insisting that if a code section does not specifically call out that exact scenario then it should be ok. So they are looking to do the bare minimum work they can get away with and I am thinking about people getting shocked or electrocuted.
 
The bare minimum as far as the NEC is concerned is way above a minimum safety regulation. Modern day automobiles are minimum safety compared to a military tank
 
The loose fitting is a never ending opinion with little merritt. In a building with metal framing, metal plumbing, metal duct, etc .... you could have all the fittings loose and still have a solid EGC path
 
I think you will also find that most ignore the expansion / deflection fittings when doing roof top solar on long runs. It can make conduit fittings loose or you end up with a run that came loose from an elbow.

You can use bonding bushings at both ends. It is overkill. It would be better to specify the need of expansion fittings or include extra supports near coupling.

Code sections is 300.7(B). Informational note has more detail regarding non plastic type conduit. (Also see 250.98 where used).
 
roger said:
The loose fitting is a never ending opinion with little merritt. In a building with metal framing, metal plumbing, metal duct, etc .... you could have all the fittings loose and still have a solid EGC path
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Agreed but I'm specifically referring to residential solar PV. If there is a ground fault that energizes a roof to wall conduit run AND only one end is bonded AND one (or more) fittings is loose AND a person touches the energized portion of the run that does not have a bushing they can be killed. That's my concern. When I was doing solar O&M I would unfortunately find loose conduit fittings quite often. And I've been zapped by touching a mounting rail or piece of EMT that wasn't properly bonded.

I guess the main question I'm hoping for feedback on is does it seem reasonable to ask for both ends of a long conduit run to have bonding bushings attached?
 
photonboy said:
I guess the main question I'm hoping for feedback on is does it seem reasonable to ask for both ends of a long conduit run to have bonding bushings attached?
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How much does a bonding bushing cost and how difficult and/or time consuming is it to install?
 
photonboy said:
I guess the main question I'm hoping for feedback on is does it seem reasonable to ask for both ends of a long conduit run to have bonding bushings attached?
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It's perfectly reasonable as long as it's getting paid for being done, as is just about anything.

However, a wire EGC can bond both ends of a run into metal enclosures without bushings
 
ggunn said:
How much does a bonding bushing cost and how difficult and/or time consuming is it to install?
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Not much and not much. In my current role I'm seeing these post-install so rework/truck rolls are part of the equation. Nobody likes going back to a finished project to do rework and I don't like asking for it but when the safety of persons is at risk I'm ok with it. But it definitely gets a lot of pushback, especially when I don't have clear and unambiguous code wording to refer to. Ideally a clear code section would end the debates, or at least minimize them. Unfortunately just appealing to safety concerns is not sufficient. Not when money is involved.

Rhetorical question here: How many people have been electrocuted over the years so someone else could save some time or a bit of money?
 
LarryFine said:
It's perfectly reasonable as long as it's getting paid for being done, as is just about anything.

However, a wire EGC can bond both ends of a run into metal enclosures without bushings
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Correct, as with bonded metal Soladeck boxes, which still rely on how well the fittings are tightened. We are often dealing with a plastic junction box on the roof end and a plastic SolarEdge inverter cabinet or Enphase combiner on the other end.
 
photonboy said:
I guess the main question I'm hoping for feedback on is does it seem reasonable to ask for both ends of a long conduit run to have bonding bushings attached?
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In what capacity? As a specifier who puts in their requirements before the job is priced? Sure. As a customer who tries to get it done after the jobs is complete, with no prior mention of it? No. As an AHJ inspector enforcing only the unamended NEC? No.

But in the latter two cases, you can check all the fittings and make sure they are secure, since the NEC requires that. As well as confirm that any NEC required expansion fittings have been installed. Both of those checks seem more valuable to me than an extra unrequired bonding bushing.

Cheers, Wayne
 
photonboy said:
Not much and not much. In my current role I'm seeing these post-install so rework/truck rolls are part of the equation. Nobody likes going back to a finished project to do rework and I don't like asking for it but when the safety of persons is at risk I'm ok with it. But it definitely gets a lot of pushback, especially when I don't have clear and unambiguous code wording to refer to. Ideally a clear code section would end the debates, or at least minimize them. Unfortunately just appealing to safety concerns is not sufficient. Not when money is involved.

Rhetorical question here: How many people have been electrocuted over the years so someone else could save some time or a bit of money?
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Are you the designer? If you are, you are not bound to design the system only to the minimum standards set by the NEC. If in your judgement it makes the installation safer, as long as it doesn't violate the NEC and it is included in the pricing of your bid, the installers can pound sand if they don't like it. That's just my opinion as a designer, you understand. :D
 
wwhitney said:
In what capacity? As a specifier who puts in their requirements before the job is priced? Sure. As a customer who tries to get it done after the jobs is complete, with no prior mention of it? No. As an AHJ inspector enforcing only the unamended NEC? No.

But in the latter two cases, you can check all the fittings and make sure they are secure, since the NEC requires that. As well as confirm that any NEC required expansion fittings have been installed. Both of those checks seem more valuable to me than an extra unrequired bonding bushing.

Cheers, Wayne
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I work for a solar financing company and I'm currently wearing two related hats, working on design standards and reviewing PV systems post install. I installed for a decade or so, then did O&M for another 5-6, now I'm here. We process hundreds of installs per month all over the country so don't have the ability to do physical QA on each one, we rely on the installers verifying the work by sending us photos and the local AHJ inspectors, which my personal experience is a bad way to ensure safety. Having hosted many inspections myself I can tell you that AHJs range from top quality electricians who know their stuff to absolute bozos who hand out green tags like candy.
 

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photonboy said:
Having hosted many inspections myself I can tell you that AHJs range from top quality electricians who know their stuff to absolute bozos who hand out green tags like candy.
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As well as absolute bozos who work the other side of the street; they write imaginary code on the spot and hold up inspections for blsht reasons.
 
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LarryFine said:
I would like to add that a bonding bushing is no better at bonding the first length of EMT than a tight connector and lock-nut, nor is it any better at compensating for loose couplings along the run.
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Agreed if metal bonded enclosures on both ends, but we more often have plastic enclosures on both ends.
 
photonboy said:
but we more often have plastic enclosures on both ends.
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You should have included that in your opening post. Why would anyone use metallic raceways between plastic boxes or enclosures? There may be bigger problems here than bonding.
 
roger said:
You should have included that in your opening post. Why would anyone use metallic raceways between plastic boxes or enclosures? There may be bigger problems here than bonding.
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I could see it outside. It does not take real long for PVC conduit outside to start drooping.
 
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