Over kill bond bushing

[Carultch]

PS: A combination EGC/GEC is still treated as a GEC. Only difference is that it is permitted to terminate to the poco-side grounding bus, rather than using an irreversible connection. One gets to be creative if there are multiple inverters connected to the other end. :angel:

Correct. It is seen as a conductor that has to follow all rules pertaining to both the EGC and GEC.

The practice I've learned as a recommended way to do this is as follows:
For circuits that have a #6 EGC or smaller, it makes sense to run a combined EGC/GEC.
For circuits that have a larger EGC, run a separate EGC and a #6 GEC. Trying to combine the EGC with the GEC is "asking for trouble". Because it becomes much more difficult to irreversibly bond larger sizes of wire, and follow all the other GEC rules.

 

[Smart $]

...
Additional question:
If your inverter has a GEC terminal inside it, that is also continuous with its metal enclosure, can this suffice? Or do you need an additional bonding bushing inside the inverter specifically because of the GEC?

The reason I ask, is that the space is limited inside a string inverter's cabinet. And it is difficult to get a bonding bushing in there, with its lug accessible. If the standard locknuts alone establish electrical continuity, and the GEC is internally bonded to the inverter enclosure, then I wouldn't see the need for the bonding bushing.
...

Bonding is per 250.64(E)(2), in short per 250.92(B)(2) through (B)(4)... so "ensured" bonding method is required... thus standard locknut only is non-compliant... but a bonding locknut is compliant [250.92(B)(4)]. A right-angle screwdriver will likely be required to torque the bonding screw.

And to clarify my earlier statement, the bonding entries and exits is with regard to ferrous raceways and enclosures. Non-ferrous metallic raceways and enclosures are considered the same as non-metallic, but I think "ensured" bonding methods employed between ferrous and non-ferrous metallic raceways and enclosures is still an effective "ensured" bonding method.

 

[Zee]

Bonding is per 250.64(E)(2), in short per 250.92(B)(2) through (B)(4)... so "ensured" bonding method is required... thus standard locknut only is non-compliant... but a bonding locknut is compliant [250.92(B)(4)]. A right-angle screwdriver will likely be required to torque the bonding screw.

And to clarify my earlier statement, the bonding entries and exits is with regard to ferrous raceways and enclosures. Non-ferrous metallic raceways and enclosures are considered the same as non-metallic, but I think "ensured" bonding methods employed between ferrous and non-ferrous metallic raceways and enclosures is still an effective "ensured" bonding method.

Hmmm that is interesting news to me.
so a locknut on a raintight steel EMT connector when entering an aluminum enclosure in a just right sized KO (not eccentric or concentric) is not to NEC? I need the gr. bushing?

I need to look out for this as many inverters and JB's and CB's are aluminum..... and hence, non ferrous, correct?

 

[Smart $]

Hmmm that is interesting news to me.
so a locknut on a raintight steel EMT connector when entering an aluminum enclosure in a just right sized KO (not eccentric or concentric) is not to NEC? I need the gr. bushing?

I need to look out for this as many inverters and JB's and CB's are aluminum..... and hence, non ferrous, correct?

When we're talking about a GEC or combination EGC/GEC, using only a standard locknut is non-compliant.

A grounding bushing is but one means of "ensured" bonding. I have no idea why everyone is so dead set on using grounding bushings. It's extra cost for the bushing itself plus the additional material and labor for the jumper compared to a bonding locknut, which is equally compliant under 250.92... unless you are dealing with a non-metallic enclosure, of course.

Yes, aluminum is non-ferrous.

 

[cowboyjwc]

I can't tell you how many boding bushings I see on plastic boxes.

 

[Carultch]

I can't tell you how many boding bushings I see on plastic boxes.

I thought with plastic boxes, you have few (if any) other options than to use a bonding bushing, in order to establish continuity from ground bar to the metal raceway(s). And a bonding bushing is the most straightforward method.

 

[ADub]

I thought with plastic boxes, you have few (if any) other options than to use a bonding bushing, in order to establish continuity from ground bar to the metal raceway(s). And a bonding bushing is the most straightforward method.

It's not too often I see metal conduit between 2 plastic enclosures. Usually one of the boxes will be metal.


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[Smart $]

It's not too often I see metal conduit between 2 plastic enclosures. Usually one of the boxes will be metal.

Still needs bonding on the plastic box end. We're talking GEC here. Thus not only "ensured" bonding but also continuity.

 

[ADub]

Still needs bonding on the plastic box end. We're talking GEC here. Thus not only "ensured" bonding but also continuity.

When you're right you're right


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[Zee]

i meant DC side, sorry. So:
EMT terminating in a steel connector into aluminum enclosure (i drilled KO)...will I need a gr bushing?

 

[Smart $]

i meant DC side, sorry. So:
EMT terminating in a steel connector into aluminum enclosure (i drilled KO)...will I need a gr bushing?

If it's a GEC, doesn't matter whether AC or DC.

 

[Carultch]

i meant DC side, sorry. So:
EMT terminating in a steel connector into aluminum enclosure (i drilled KO)...will I need a gr bushing?

If it contains a GEC, yes.
If there are ring knockouts remaining and over 250V to ground, yes.
If none of the above is true, standard locknuts establish your ground, no matter what combination of metals form your enclosure and raceway system.

 

[Shawn pavich]

Most of the box connecters now a days are not the flat lock ring type that you find on liquid tight are any plastic connecter.they have a slanted edge on them that bites into encolsure and are listed for bonding

 

[Smart $]

Most of the box connecters now a days are not the flat lock ring type that you find on liquid tight are any plastic connecter.they have a slanted edge on them that bites into encolsure and are listed for bonding

They only qualify as standard locknuts per UL and in use under 250.92(B).

 

[Carultch]

Most of the box connecters now a days are not the flat lock ring type that you find on liquid tight are any plastic connecter.they have a slanted edge on them that bites into encolsure and are listed for bonding

Our discussion is whether standard grounding practices are sufficient (standard locknuts, Myers hubs, EMT/FMC/LFMC connectors, compression connectors), or whether one needs to install a bonding bushing/other more substantial means of grounding.

And it is application specific, depending on the details of what is inside the raceway.

 

[Shawn pavich]

Bonding at service is very clear,I thought we were talking about 250 volts or higher that's were I have had trouble with inspectors, and co workers fighting me on were to use bond bushing,the parts houses out here only have 3" bonding locknuts with the screw, why would they carry anything smaller,most likely if you need anything smaller you are not going to have a clean hole there for a bonding locknuts would be worthless, and if you do have a clean hole then you would be wasting your money on a bonding locknut and a ground bushing. a listed fitting such has a box connecter that is listed for bonding would be good enough from what I have Seen even at homedepot they are most likely listed for bonding if it's a metallic connecter. and I think that is ex#4 on 250 volts or higher,when I used to buy metallic box connecters I never really looked at the locknut until I started doing solar, the lock nuts are different from plastic connecters

 

[jaggedben]

I can get bonding locknuts in 1/2" size or up from my supply house, and I've had inspectors ask for them on raceway connections for GECs to avoid the choke effect and comply with 250.64(E). They will allow a bonding locknut if the enclosure is bonded. As I see it they really ought to allow any listed fitting to create that bond (under 250V), but this is not really a battle worth fighting for me.

With that said, I've never understood why bonding locknuts are an allowed means to bond within concentric knockouts or reducing washers, since the bonding screw will almost certainly still be on the washer or one of the outer concentric knockout rings. With eccentric I guess you could orient the locknut away from the larger knockouts.

 

[Carultch]

With that said, I've never understood why bonding locknuts are an allowed means to bond within concentric knockouts or reducing washers, since the bonding screw will almost certainly still be on the washer or one of the outer concentric knockout rings. With eccentric I guess you could orient the locknut away from the larger knockouts.

I don't understand either. Perhaps you are supposed to bring a bonding jumper to the bonding locknut's screw. I have yet to find an application to use a bonding locknut in practice.

And I think orienting the screw away from the larger KO's on a set of eccentric tangential KO's, is easier said than done. Likely that is on the inner edge of the opening, toward the back wall of the enclosure. Plus, unless your raceway is free to rotate, you have no control over where the bonding screw ends up in its rotation.

 

[Smart $]

... With that said, I've never understood why bonding locknuts are an allowed means to bond within concentric knockouts or reducing washers, since the bonding screw will almost certainly still be on the washer or one of the outer concentric knockout rings. With eccentric I guess you could orient the locknut away from the larger knockouts.

I don't understand either. ...

While I'm a bonding locknut over bushing advocate, I recommend using the most appropriate for the conditions... so don't forget about possibly using a bonding wedge either.

 

[Zee]

If it contains a GEC, yes.
If there are ring knockouts remaining and over 250V to ground, yes.
If none of the above is true, standard locknuts establish your ground, no matter what combination of metals form your enclosure and raceway system.

Thanks Carultch, that is what I was looking for.

Anybody disagree on the following statement?
ON DC SIDE, over 250 VDC, no GEC, a steel connector on EMT conduit with lock-ring (only) into an aluminum enclosure KO (not eccentric or concentric and no reducing washers) = code compliant?