250.92(B)(3)

[infinity]

So does that mean you accept that say out of the bottom of a meter base an EMT connector with its included locknut complies by itself with 250.92(B)?

No. Standard locknuts are explicitly mentioned as not complying with 250.92(B). Doesn't matter if that standard locknut is on RMC, an EMT connector, offset nipple, or any other metal fitting, raceway or connectors. Standard locknuts are permitted for mechanical connection but not for bonding.

 

[wwhitney]

No. Standard locknuts are explicitly mentioned as not complying with 250.92(B). Doesn't matter if that standard locknut is on RMC, an EMT connector, offset nipple, or any other metal fitting, raceway or connectors. Standard locknuts are permitted for mechanical connection but not for bonding.

You're referring to the part of 250.92(B) that reads "Standard locknuts or bushings shall not be the only means for the bonding required by this section."

It seems to me that you are reading this as "standard locknuts shall not be any part of the means of bonding." Whereas the actual text uses the word "only," as in locknuts only.

I agree locknuts only does not comply with 250.92(B). But a locknut plus a threadless connector, in a combination that has been tested under UL 514(B) for resistance and current, is not a case of standard locknuts being the only means of bonding. It explicitly complies with 250.92(B) as specified in subsection (3).

Cheers, Wayne

P.S. Another example would be a standard locknut on one side, and a bonding locknut on the other side (the kind with a separate screw with sharp point that you use to jab the enclosure). That relies on a standard locknut as part of the assembly, but it is not a case of standard locknuts being the only means of bonding.

Now replace the bonding locknut with a threadless EMT connector. Same situation. Both comply with 250.92(B).

 

[infinity]

You're referring to the part of 250.92(B) that reads "Standard locknuts or bushings shall not be the only means for the bonding required by this section."

It seems to me that you are reading this as "standard locknuts shall not be any part of the means of bonding." Whereas the actual text uses the word "only," as in locknuts only.

I agree locknuts only does not comply with 250.92(B). But a locknut plus a threadless connector, in a combination that has been tested under UL 514(B) for resistance and current, is not a case of standard locknuts being the only means of bonding. It explicitly complies with 250.92(B) as specified in subsection (3).

Cheers, Wayne

P.S. Another example would be a standard locknut on one side, and a bonding locknut on the other side (the kind with a separate screw with sharp point that you use to jab the enclosure). That relies on a standard locknut as part of the assembly, but it is not a case of standard locknuts being the only means of bonding.

Now replace the bonding locknut with a threadless EMT connector. Same situation. Both comply with 250.92(B).

I see how you're reading this but in 40 years in this trade I've know of no one that agrees with your interpretation. The standard locknut whether it comes in a box or on a connector cannot be used for bonding the raceway. If fact with something like the meter base with the EMT connector that you've mentioned two standard locknuts on a piece of RMC would provide a much better electrical connection than the EMT connector with a single standard locknut. Two locknuts would cut into the paint on both sides of the meter enclosure. A connector with single locknut would only cut into the paint on one side. The EMT connector shoulder against the paint would provide little to no connection to the metal enclosure.

 

[Pinnie]

I think waynes arguement is a valid case for the clarification needed in this section. just a quick tidy and it would be perfect.

 

[wwhitney]

I see how you're reading this but in 40 years in this trade I've know of no one that agrees with your interpretation.

Right, I'm coming at this from what the text of the NEC says, rather than any absorbed wisdom from the community. It's possible the two are misaligned.

I'll just point out that as far as I know, nobody has paid to test two standard locknuts for bonding and grounding, while an EMT connector and its locknut is tested for current and resistance under UL 514(B). On the other hand, I do see that it is odd that the shoulder on an EMT connector (or a threadless RMC connector) is smooth and will not bite into the enclosure.

What's your opinion on a standard locknut plus a pointy bonding locknut on the threaded end of RMC, does that comply with 230.92(B)?

Cheers, Wayne

 

[wwhitney]

Hmm, the plot thickens a bit. I decided to check the 1987 NEC to see what is says. The equivalent section is 250-72 "Methods of Bonding Service Equipment". Subsection (c) says:

"(c) Threadless Couplings and connectors made up tight for rigid metal conduit, intermediate metal conduit and electrical metallic tubing. Standard locknuts or bushings shall not be used for the bonding required by this section."

So on the one hand that is exactly what infinity says, you can't use a standard locknut with an EMT connector (or threadless RMC connector). But on the other hand, how else do you use a standard connector which comes with a threaded bit that sticks into the enclosure?

If the answer is "using a bonding locknut with the connector", then the inclusion of "connectors" in (c) seems completely redundant. It could just refer to threadless couplings. Because bonding locknuts are already covered in (e):

"(e) Other Devices. Other approved devices, such as bonding-type locknuts and bushings."

This leaves me a bit confused, unless the second sentence of (c) is saying "don't use a separate standard locknut that comes with the threadless connector; use the locknut provided with the connector, as that is the one that has been tested in combination with the connector." If that's the intention, it's not very clear.

Cheers, Wayne

 

[wwhitney]

On the topic of 250.92(B), curious about other's ideas about whether the following examples would be compliant with the text.

(a) RMC threaded end into service enclosure, with standard locknut on one side and pointy bonding locknut on the other.
(b) A compression style snap-in EMT connector, no locknuts involved.

Thanks,
Wayne

 

[wwhitney]

OK, a little more history. 1981 NEC 250-72(c) just referred to "threadless couplings" with no mention of connectors. Then PI 5-83 (250-72(c)) for the 1984 NEC (which isn't available through Free Access at npfa.org/70, but the ROP and ROC for it are on the website) proposed to change the word "couplings" to "fittings". The substantiation was:

The word "couplings" per se does not include threadless connectors which when screwed into threaded hubs or bosses, or used with grounding or bonding ocknuts or bushings appear to be a satisfactory and commonly accepted method of obtaining electrical continuity at services.

The CMP accepted but decided to change "couplings" to "couplings and connectors". This apparently opened up the 1984 NEC to the interpretation I was proposing that a threadless connector along with its locknut suffices, which was not the intention per the above substantiation. And so the 1987 NEC added that sentence about not using standard locknuts to 250-72(c). And that notion eventually migrated to the parent text of what is now 250.92(B).

So the answer to my question "how else do you use a standard connector which comes with a threaded bit that sticks into the enclosure?" was apparently "by screwing them into threaded hubs or bosses," at least in 1984. I guess the hubs with straight threads vs tapered threads kerfuffle postdates that time.

Thus I reluctantly agree that the intention behind 250.92(B) is that an EMT connector with a locknut is not sufficient, and you would need at a minimum to add a bonding wedge or bonding locknut to the EMT connector. But the present wording of 250.92(B) is evidently not sufficiently clear. So I guess that's another PI on my list for this month.

Cheers, Wayne

 

[wwhitney]

But the present wording of 250.92(B) is evidently not sufficiently clear. So I guess that's another PI on my list for this month.

OK, I came up with changing the subject of 250.92(B)(3) from "Threadless couplings and connectors" to "Threadless connections on couplings and connectors." That makes it clear that for a connector, the allowance applies only to the threadless side of the connector, not the side that is normally used with a locknut. Other options 250.92(B) will be required for maintaining electrical continuity between the connector and the enclosure at a service.

Cheers, Wayne