Listed Conduit Hubs VS “Myers” Hubs

[yesterlectric]

It’s been asked here but has never been clarified. Even one of the people who’s on Mike’s DVD team suggests that when applying 250.92, that Myers hubs (trade name most of use for these conduit hubs that have a UL listing) don’t satisfy the requirement for listed hubs and thus you still need either need a bonding locknut or grounding bushing. It seems the thinking is only the hubs that bolt onto enclosures suffice. However has anyone ever found any clear evidence of this besides the opinion of some in the industry? UL white book doesn’t seem to suggest this. If the NEC truly was meaning to say this then they probably should’ve written it differently. They probably should’ve said “enclosures with integral hubs” instead of if you use listed hubs.

 

[DrSparks]

They make Myers hubs with am integral ground clamp. I assume you are referring to being listed for bonding. I believe they are and the same rules apply to conduit terminated with locknuts. Must be wrench tight with with the teeth digging into the metal and piercing any painted surface and not through concentric KOs.

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[yesterlectric]

They make Myers hubs with am integral ground clamp. I assume you are referring to being listed for bonding. I believe they are and the same rules apply to conduit terminated with locknuts. Must be wrench tight with with the teeth digging into the metal and piercing any painted surface and not through concentric KOs.

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No that’s not what I’m referring to. If you use listed hubs (which is what is in question here) you don’t have to have a grounding bushing and a wire jumper because the bond to the service disconnect enclosure is sufficient. If you don’t use listed hubs, and you use something like locknuts on either side of a piece of RMC or an EMT connector with EMT, then you have to use the grounding bushing with the wire jumper. I’m wondering how those making the claim that the Myers hub doesn’t constitute a listed hub for the purpose of this section, substantiate that statement.

 

[augie47]

Last time I discussed this with the UL Engineer I was told there are (2) distinct listing on "Myers" hubs: DWTT and KDER
The KDER, which has the means for a bonding jumper, qualifies to be used in a 250.92 (Service) install where as the DWTT does not.
An example is CrouseHinds HUB-100 vs HUB100-B, the one without the B does not qualify.;

Here is your substantiation:
The ones identified with the document provided are only covered under UL Product DWTT (E11853) and not KDER (E24264). They were missing the suffix “B” hence HUB-100B versus HUB-100, the model with the “B” complies, the model without the “B” does not comply for service equipment applications per 250.92.
Link to UL Product Category KDER;

http://productspec.ul.com/details.php?ccn=KDER
Hope this helps.


Jeffrey A. Fecteau CBO

Senior Regulatory Engineer

Distinguished Member of Technical Staff UL

----------------------------------

 

[DrSparks]

I'm confused. 250.92 deals with bonding of metal raceways for services. The way I interpret that is you don't need a ground bushing if your hole is appropriately sized and the lock nuts are wrench tight. Has this code changed recently?

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[yesterlectric]

Last time I discussed this with the UL Engineer I was told there are (2) distinct listing on "Myers" hubs: DWTT and KDER
The KDER, which has the means for a bonding jumper, qualifies to be used in a 250.92 (Service) install where as the DWTT does not.
An example is CrouseHinds HUB-100 vs HUB100-B, the one without the B does not qualify.;

Here is your substantiation:
The ones identified with the document provided are only covered under UL Product DWTT (E11853) and not KDER (E24264). They were missing the suffix “B” hence HUB-100B versus HUB-100, the model with the “B” complies, the model without the “B” does not comply for service equipment applications per 250.92.
Link to UL Product Category KDER;

http://productspec.ul.com/details.php?ccn=KDER
Hope this helps.


Jeffrey A. Fecteau CBO

Senior Regulatory Engineer

Distinguished Member of Technical Staff UL

----------------------------------

I don’t see how this is a substantiation. In the example described, hub-100b simply has the lug to allow a wire type of bond. It’s no different than if you had used two lock nuts on either side of an enclosure and used a grounding bushing. The code gives several means of doing it. One of them is listed hubs. The other is grounding bushings (which have a wire connection). If you use whatever the code is calling a list it up you shouldn’t have to add the wire because the bond to the enclosure should be sufficient.

 

[yesterlectric]

I'm confused. 250.92 deals with bonding of metal raceways for services. The way I interpret that is you don't need a ground bushing if your hole is appropriately sized and the lock nuts are wrench tight. Has this code changed recently?

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It’s not exactly recent but yes more is required on the wind side of the service and it’s not just if you have eccentric or concentric knockouts.

 

[augie47]

I'm confused. 250.92 deals with bonding of metal raceways for services. The way I interpret that is you don't need a ground bushing if your hole is appropriately sized and the lock nuts are wrench tight. Has this code changed recently?

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250.92 (B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s)

 

[DrSparks]

250.92 (B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s)

I see that. That only applies to service raceways correct? I always use PVC so I'm rusty there. Locknuts are ok for feeder raceways?

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[yesterlectric]

I guess this will go down as another one of those questions on this that was brought up but never really answered. I think they should revise the code to make it clear if they are going to say that only certain listed conduit hubs are acceptable.

It might be that the intent was to say that if you have the bolt on style hubs that you don’t have to run an additional ground wire to those because the bolt provides an additional tight bond to the metal enclosure. If this was the intent, then I think they should’ve said that “listed hubs that are integral with the enclosure” are acceptable. Otherwise they should just remove the sentence about listed hubs because there’s no need to have such a sentence if it’s only intended to approve listed hubs that have a grounding lug.

 

[wwhitney]

I'm confused by this discussion of "listed hubs". 250.92(B) has two relevant options:

(2) Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
(4) Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers

Option (2) doesn't use the word "listed." A Meyers hub that is listed to UL category KDER (Ground and Bonding Equipment) would obviously fit category (4). And if the intention was to require a Meyers hub to be so listed, then option (2) should specify "integral hubs" or "factory hubs" or something. But it doesn't, the language of "threaded hubs on enclosures" seems to me to cover any Meyers hub, not just those listed to KDER.

Or are people reading "on enclosures" to already mean "integral to the enclosure"?

Cheers, Wayne

 

[yesterlectric]

I'm confused by this discussion of "listed hubs". 250.92(B) has two relevant options:

(2) Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
(4) Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers

Option (2) doesn't use the word "listed." A Meyers hub that is listed to UL category KDER (Ground and Bonding Equipment) would obviously fit category (4). And if the intention was to require a Meyers hub to be so listed, then option (2) should specify "integral hubs" or "factory hubs" or something. But it doesn't, the language of "threaded hubs on enclosures" seems to me to cover any Meyers hub, not just those listed to KDER.

Or are people reading "on enclosures" to already mean "integral to the enclosure"?

Cheers, Wayne

It doesn't say hubs listed for grounding and bonding. It just says listed hubs. If they needed to be listed for grounding and bonding then it would say so, much like in 250.8 it says you can use listed pressure connectors AND connectors listed for grounding and bonding. If it doesn't specifically say that the hubs have to be listesd for grounding and bonding, then I don't interpret it so.

 

[kwired]

I guess this will go down as another one of those questions on this that was brought up but never really answered. I think they should revise the code to make it clear if they are going to say that only certain listed conduit hubs are acceptable.

It might be that the intent was to say that if you have the bolt on style hubs that you don’t have to run an additional ground wire to those because the bolt provides an additional tight bond to the metal enclosure. If this was the intent, then I think they should’ve said that “listed hubs that are integral with the enclosure” are acceptable. Otherwise they should just remove the sentence about listed hubs because there’s no need to have such a sentence if it’s only intended to approve listed hubs that have a grounding lug.

Section Augie quoted answers this.

250.92 (B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s)

A bolt on hub is not a standard locknut or bushing. Enclosure with integral hub isn't standard locknut or bushing either.

A meyers hub - most don't have your typical standard locknut but I would think it comes down to listing of them on whether you can treat them as more than standard locknut. And yes there are versions with a bonding lug attached to them, which may or may not mean anything about the general bonding ability of the locknut.

 

[wwhitney]

It just says listed hubs.

Again, it doesn't even say that, 250.92(B)(2) doesn't use the word listed. It just says "threaded hubs on enclosures."

Cheers, Wayne

 

[yesterlectric]

Again, it doesn't even say that, 250.92(B)(2) doesn't use the word listed. It just says "threaded hubs on enclosures."

Cheers, Wayne

Actually, 2020 they added the term listed hubs, but that to me doesn't make much of a difference in the question I had. I don't see how the listed hub (commonly called Myers hub) doesn't meet the rule of 250.92 B 2. In one of Mike's code update videos, an inspector from Massachusetts elluded to a thnking that a Myers hub doesn't constitute a hub for the purpose of 250.92, but I don't see anythign that substantiates that. The only thing I get is that perhaps one needs to be careful of the opinion of the inspector and if possible try not to rely on things like Myers Hubs. There's some applications, such as safety switches used as service equipment (some are so rated) where the manufacturer provided listed accessories provide no provisions for an extra wire for a grounding bushing (or wire for connection to a Mysers Hub so equipped).

 

[wwhitney]

Actually, 2020 they added the term listed hubs, but that to me doesn't make much of a difference in the question I had.

Thanks for the correction. I actually checked the 2020 NEC to see if there was a change, but managed to completely miss the added the word. Too bad the online version at nfpa.org/70 doesn't have shading for changes.

So now the question (for the 2020 NEC) is whether the use of the word "listed" in a section of article 250 implicitly means "listed for grounding and bonding." I would say there is a reasonable argument that it does, that there's no need to spell out "listed for grounding and bonding" given the context. Not sure about this one.

Cheers, Wayne

 

[kwired]

Actually, 2020 they added the term listed hubs, but that to me doesn't make much of a difference in the question I had. I don't see how the listed hub (commonly called Myers hub) doesn't meet the rule of 250.92 B 2. In one of Mike's code update videos, an inspector from Massachusetts elluded to a thnking that a Myers hub doesn't constitute a hub for the purpose of 250.92, but I don't see anythign that substantiates that. The only thing I get is that perhaps one needs to be careful of the opinion of the inspector and if possible try not to rely on things like Myers Hubs. There's some applications, such as safety switches used as service equipment (some are so rated) where the manufacturer provided listed accessories provide no provisions for an extra wire for a grounding bushing (or wire for connection to a Mysers Hub so equipped).

250.92(B)(2) is identical in NFPA's free access versions of 2017 and 2020 and both say "or listed threaded hubs". Which might have intended to mean an integral hub and not a myers type hub?

 

[wwhitney]

250.92(B)(2) is identical in NFPA's free access versions of 2017 and 2020 and both say "or listed threaded hubs".

I do not see the word "listed" in the 2017 version of the NEC on nfpa.org/70.

I looked up the 2020 PI that added the word "listed" to 250.92(B)(2). The panel statement was "The change will affirm that hubs used for a service installation must be listed in accordance with Section 344.6." As 344.6 just says "RMC, factory elbows and couplings, and associated fittings shall be listed," that's a strong argument that the listing required by 250.92(B)(2) is just UL DWTT, not UL KDER.

Cheers, Wayne

 

[kwired]

I do not see the word "listed" in the 2017 version of the NEC on nfpa.org/70.

I looked up the 2020 PI that added the word "listed" to 250.92(B)(2). The panel statement was "The change will affirm that hubs used for a service installation must be listed in accordance with Section 344.6." As 344.6 just says "RMC, factory elbows and couplings, and associated fittings shall be listed," that's a strong argument that the listing required by 250.92(B)(2) is just UL DWTT, not UL KDER.

Cheers, Wayne

This what shows up on my screen, have to run out to truck to see what my printed copy might say. Haven't purchased or had to yet a 2020 so on line access is what I have used when referencing that.

 

[paulengr]

See

https://code-authorities.ul.com/wp-content/uploads/2014/04/ul_ConduitHubs.pdf

DWTT is Listing for service entrance. It can also optionally be Listed under KDER for grounding and bonding, not the other way around.

Kind of reminds me of when I’ve seen external bonding cables added to LFMC in division 1 (hazardous locations) service. Obviously the LFMC or connectors that are clearly Listed aren’t sufficient by themselves, Lusted or not. And many things do not require Listing (common hardware). It comes down to when do we cross the line.