Meyer's Hub

[Karl H]

I'm looking at a Meyers hub right now and I think I'm going to change
my opinion. What does the White Book say? If you use channel locks to tighten
a Meyers Hub it does scratch the paint of a 3R enclosure.

 

[jeremysterling]

I'm looking at a Meyers hub right now and I think I'm going to change
my opinion. What does the White Book say? If you use channel locks to tighten
a Meyers Hub it does scratch the paint of a 3R enclosure.

I try to put the channellocks on the lock nut rather than the fitting. The O-ring can jump out or tear if you turn the main body of the fitting. You may scrape the paint off with the hub's teeth at the expense of watertightness when the O-ring fails. IMO, when the locknut is tightened, it pulls the fitting's teeth into the enclosure while safely compressing the O-ring.

 

[Karl H]

I try to put the channellocks on the lock nut rather than the fitting. The O-ring can jump out or tear if you turn the main body of the fitting. You may scrape the paint off with the hub's teeth at the expense of watertightness when the O-ring fails. IMO, when the locknut is tightened, it pulls the fitting's teeth into the enclosure while safely compressing the O-ring.

When I hand tighten a Meyers Hud the distance from the top tooth
to the bottom tooth is 1/16th of an inch. So when made "Wrench Tight"
I'm going to have to say yes it is suitable for grounding/bonding.
But, then again my opinion doesn't really matter. The AHJ or IEEE opinion
does.

 

[RUWired]

There are grounding type myers hubs out there.

http://www.crouse-hinds.com/crousehinds/pdf/CH62318C-0077.pdf

 

[Karl H]

Even the half inch Meyer's Hub I have has four threads in contact. I can't tell the
manf. name I don't think it's a DOT. I also wouldn't say that a Meyer's
hub has a standard lock nut either. I have to admit this is the first time I
have ever really looked at a Meyer's this closely before. Can anyone reff the IEEE white book as I don't have one in my home office?

 

[brantmacga]

IMO, I would agree that the lock nut that comes with a "standard male 'Myers' hub" fitting is a trade standard lock nut. However, in the past I have used female Myers hubs that do not include a locknut as part of its standard assembly.

Some male Myers hubs come with a bonding style locknut.

what is a female myers hub?

 

[mweaver]

Screw-type Hubs and Section 250.92(B)

Screw-type Hubs and Section 250.92(B)

This question came up during a training event recently in Kansas City so I contacted a UL staff engineer associate I network with, and his information and insight was helpful.

He stated: In reality, the use of this screw-type (Cooper-Myers or T&B) hub without its optional grounding lug to comply with Section 250.92(B) will be an AHJ call because of a (sort of) catch 22. The following is a summation of what he informed me over the phone ?


Section 250.92(B) recognizes other listed devices (under list item 4)

Both T&B and Cooper (Myers) produce these screw-type hubs which are actually listed under the 2008 UL White Book?s category DWTT (pg 103) as a conduit fitting. Both companies produce these hubs with an optional grounding screw for the connection of a bonding jumper. Under this listing category (DWTT), if they are listed, they are listed for grounding above and below 250 volts. Section DWTT does not mention continuity required by the NEC at service equipment. This DWTT listing (for grounding) includes the Cooper and T&B hubs with and without the optional grounding screw. These hubs are listed for grounding (under UL?s DWTT) and Section 250.92(B) recognizes other listed devices. For some jurisdictions, this may suffice.




For some AHJs, issue of 250.92(B) may surround the hub?s sealing ring and the hub?s ability (or lack of) to maintain both inside and outside metal-to-metal contact between the hub and the enclosure. (This would assume a non-enamel [or paint removed by hand] metallic enclosure, since no device or fitting has ever been evaluated or listed by UL listed to peel paint on its own and satisfy any grounding or bonding requirements.)




The catch 22 ?

The UL White Book also contains a grounding category (KDER pg 180) which addresses fittings, such as hubs to provide a raintight or liquidtight connection, and their compliance (under KDER) to provide electrical continuity required by the NEC at service equipment and for circuits rated over 250 V. While the Cooper-Myers hubs were not checked for listing under KDER, the only T&B hub listed under the KDER category is for ?? trade size, which is not extremely helpful for most service installations. The UL representative stated that the use of these DWTT listed hubs with their optional grounding screw and correctly sized line side bonding jumper should satisfy the requirements of Section 250.92(B) for any jurisdiction which may choose to question their use without the optional grounding screw and jumper.



He stated: As an AHJ (and he used to be an AHJ ?), he would require the hub be equipped with the optional grounding screw and a properly sized and installed line side bonding jumper to provide compliance with the bonding requirements of Section 250.92(B).


I hope this is helpful,
mweaver

 

[tom baker]

Hello Ryan.
I looked into this issue some time ago, and found that a meyers hub is listed as a fitting, same as a locknut. There is a version of the Meyers hub available with a grounding ring, IE the locking has a screw for the attachment of a grounding jumper.

 

[LJSMITH1]

A "Myers" hub has a special locknut - not a standard locknut. It has a wide flange with large, serrated teeth on it.

The fitting is designed to be assembled into the panel and the locknut tightened while holding the body of the hub. The increasing clamping force, combined with the rotation of the nut, will scour the paint from the surface of the metal directly across from the teeth. This will sufficiently bond the fitting to the enclosure, while maintaining a watertight seal. If you hold the nut and turn the body, you are less likely to create an electrical bond, while taking a chance that the o-ring or flat rubber gasket will 'extrude' out from under the hub body and compromise the water resistance feature.

In addition, these fittings are typically only designed for Rigid tapered threads, not straight connector threads.

The fitting is listed under UL514B and complies with standard fitting requirements.

 

[Karl H]

Well, I think that sums it up. I guess I have to return to my original
opinion, Bonding bushing required.

 

[Karl H]

A "Myers" hub has a special locknut - not a standard locknut. It has a wide flange with large, serrated teeth on it.

The fitting is designed to be assembled into the panel and the locknut tightened while holding the body of the hub. The increasing clamping force, combined with the rotation of the nut, will scour the paint from the surface of the metal directly across from the teeth. This will sufficiently bond the fitting to the enclosure, while maintaining a watertight seal. If you hold the nut and turn the body, you are less likely to create an electrical bond, while taking a chance that the o-ring or flat rubber gasket will 'extrude' out from under the hub body and compromise the water resistance feature.

In addition, these fittings are typically only designed for Rigid tapered threads, not straight connector threads.

The fitting is listed under UL514B and complies with standard fitting requirements.

What about this?
For some AHJs, issue of 250.92(B) may surround the hub?s sealing ring and the hub?s ability (or lack of) to maintain both inside and outside metal-to-metal contact between the hub and the enclosure. (This would assume a non-enamel [or paint removed by hand] metallic enclosure, since no device or fitting has ever been evaluated or listed by UL listed to peel paint on its own and satisfy any grounding or bonding requirements.)

 

[LJSMITH1]

What about this?
For some AHJs, issue of 250.92(B) may surround the hub?s sealing ring and the hub?s ability (or lack of) to maintain both inside and outside metal-to-metal contact between the hub and the enclosure. (This would assume a non-enamel [or paint removed by hand] metallic enclosure, since no device or fitting has ever been evaluated or listed by UL listed to peel paint on its own and satisfy any grounding or bonding requirements.)

There is no requirement that I am aware of that specifiies that a fitting must electrically bond to both sides of the enclosure wall. One side is usually sufficient, and will pass the ground fault test in UL514B (ex: a 2" hub would need to withstand 3900A for 6 seconds without arcing or visible damage).

If there is ever a question if serrations on locknuts will remove paint, all one needs to do to verify, is try it, and remove it. It may not be as 'clean' as a wire -brushed or sanded area, but it should be sufficient. When in doubt, the installer should always remove the coating by hand first.

As far as I know, UL has not developed a test, or included a 'paint removal' requirement in UL514B. Perhaps they will in the future.

The two things that affect a fitting's ability to handle that kind of current are surface contact area and contact pressure. If the locknut does its job, it should provide plenty of surface area (note the large flange on the hub locknut), and the rubber gasket has a certain durometer to resisist extrusion, while providing sealing and provide the amount of compressive force the locknut needs to carry the current.

 

[Karl H]

There is no requirement that I am aware of that specifiies that a fitting must electrically bond to both sides of the enclosure wall. One side is usually sufficient, and will pass the ground fault test in UL514B (ex: a 2" hub would need to withstand 3900A for 6 seconds without arcing or visible damage).

If there is ever a question if serrations on locknuts will remove paint, all one needs to do to verify, is try it, and remove it. It may not be as 'clean' as a wire -brushed or sanded area, but it should be sufficient. When in doubt, the installer should always remove the coating by hand first.

As far as I know, UL has not developed a test, or included a 'paint removal' requirement in UL514B. Perhaps they will in the future.

The two things that affect a fitting's ability to handle that kind of current are surface contact area and contact pressure. If the locknut does its job, it should provide plenty of surface area (note the large flange on the hub locknut), and the rubber gasket has a certain durometer to resisist extrusion, while providing sealing and provide the amount of compressive force the locknut needs to carry the current.

I understand everything your saying and I agree. But, if it isn't
"Listed" for the purpose, we can't use it.

 

[mweaver]

Paint removal for grounding and bonding

Paint removal for grounding and bonding

LJsmith1,

I am unable to comment on your statement: "There is no requirement that I am aware of that specifiies that a fitting must electrically bond to both sides of the enclosure wall.”
This is outside my knowledge base (as it may apply to UL514B).

But…

My understanding is that this requirement does in fact exist for the bonding of over 250 volts in Section 250.97 (Locknut inside & out -or- firmly seated shoulder outside and locknut inside, etc).
Am I misunderstanding this?


With regards to clean surfaces in Article 250, this is addressed in two locations:

Part I – General Requirements for Grounding and Bonding (applicable to all grounding and bonding)

250.12 Clean Surfaces. Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.

-and-

Part V - Bonding Requirements (applicable to all bonding)

250.96 Bonding Other Enclosures.
(A) General. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non–current-carrying parts that are to serve as grounding conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or be connected by means of fittings designed so as to make such removal unnecessary.


While this phrase: “or be connected by means of fittings designed so as to make such removal unnecessary” appears in both these Code sections, I have been informed that no such fittings have ever been submitted to UL for evaluation of this feature, hence no product is listed to perform this “removal” function (It must be removed by hand prior to making the fitting connection). The UL White Books Section DWTT notes that this listing for said products is only applicable "where installed in accordance with the NEC".

We are all familiar with certain locknuts which can in fact peel paint on some enclosures, but their individual product listing for grounding under the DWTT White Book Section is predicated upon “clean surfaces”, and the requirements of Section 250.12 for grounding and bonding and 250.96 for the bonding of Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non–current-carrying parts that are to serve as grounding conductors.

My understanding is that locknuts peeling paint is not a certainty of any particular grounding integrity.

Your statement “If there is ever a question if serrations on locknuts will remove paint, all one needs to do to verify, is try it, and remove it. It may not be as 'clean' as a wire -brushed or sanded area, but it should be sufficient.” Gives me pause as to “how sufficient” because no product has ever been listed for grounding with its individual capability to peel paint.

This is my understanding. Please help me out here if you have information which negates this. I would be delighted to be corrected on this.

If this is in fact correct then I, like many, have misunderstood the paint removal requirement for years, which is why I am now a firm believer in the statement that: Enamel is NOT your friend…

mweaver

 

[ryan_618]

I was away from the computer over the weekend, so I was unable to participate in the discussion after I posted it.

I think a bond bushing is required, and I appreciate all of your input.

 

[LJSMITH1]

I wanted to add some information regarding these Locknut Serrations; specifically their ability to remove enclosure paint to establish electrical bonding. Also, I wanted to respond to KarlH's comment about UL never evaluating this feature. I did a little more research and I found something that may be enlightening to everyone.

Back on June 1st, 1992, UL released a fact-finding research study called "Report of Research on Conduit Fitting Ground Fault Current Withstand Capability". This report was done to help validate and refine the ground fault current testing requirements in UL514B, as well as address concerns expressed regarding the ability of conduit fittings to carry ground-fault current - no matter what the metal alloy or design type.

The testing utilized a standard, painted, panel enclosure (such as a C/B panel) and short lengths of EMT coupled with various manufacturers of zinc or steel compression or set screw connectors. The paint was a standard grey, baked-on acrylic enamel that was a nominal .001" thick.

Each fitting was assembled per the manufacturers instruction (locknut hand tight plus 1/4 turn with a hammer and standard screwdriver) and subjected to test currents and times specified for the trade size under test. Over 310 fitting samples were tested.

On page 24 of the report, 2nd paragraph, UL states:

"A visual examination of all conduit fittings with die-cast zinc locknuts showed that there were three different constructions of the locknuts. The three constructions differed in that the surface of the locknut contacting the enclosure was either flat, nibbed, or serrated. The sample assemblies with die cast zinc locknuts that did NOT complete the Current Test with acceptable results had locknuts with flat or nibbed surfaces. All fittings having die-cast zinc locknuts with serrations consistently penetrated through the enclosure paint and provided better electrical contact between the fitting and the metal of the enclosure, than did the locknuts with flat or nibbed surfaces."

We were one of the first to develop serrations on the die-cast zinc locknuts around 1981, with the idea of promoting enhanced bonding and grounding capabilities. After the report came out in 1992, we noticed that some of our competitors had copied the idea. Unfortunately, for unknown reasons, we did not patent this feature in 1981 (I was still in school...not even thinking about fittings.. :roll

So, in summary, yes, serrations can cut through enamel paint to establish suitable bonding. The only caveat is what I said before. The fitting body must be held stationary while tightening the locknut (i.e. tighten the setscrew or compression nut FIRST, before the locknut). Obviously the fitting body will not cut through the paint on the outside of the enclosure, and with the results of these tests, it appears that it is not necessary to carry the specified ground fault currents. Thie UL514B specification is developed IAW NEC 250.12 & 250.96.

I hope this answers many questions.

 

[mweaver]

NEC compliance with 110.3(B), 250.12 & 250.96

NEC compliance with 110.3(B), 250.12 & 250.96

LjSmith1,

I do want to thank you for sharing this information. I have read your post three times, and I am still unsure how this information is actually helpful for me (enlightening, yes very ? helpful, not really ?). I mean no disrespect here? I am only acknowledging that I am slow ? so please bear with me, because I am in need of this clarification. It is in conflict with what I have been told, and what I can read and determine for myself.

It is obvious that you are an expert in this area, and I do respect that. This is what you do for a living and you quite notably have access to UL information that is beyond the reach of the typical installer or building official.

You have stated that you hope that your information answers many questions, but for me, it has only created additional questions. You are citing an obscure (at least for me) document from 1992 which the typical installer, designer or building official does not have access to and you seem to be citing this particular document to reinforce that: ?serrations can cut through enamel paint to establish suitable bonding?. This is of course based upon the fact that you are using a locknut which has serrations and an enamel enclosure whose paint is .001? thick. The biggest issue I have with your information (and your resulting statement) is that none of this information appears to be reflected in the 2008 NEC or 2008 UL White Book language (which is readily available to all of us). This makes it difficult for me to use on an everyday basis for determining compliance with 110.3(B), 250.12 & 250.96.

For me, your last sentence was in fact the most helpful, if I did in fact understand it correctly. You stated: ?Thie UL514B specification is developed IAW NEC 250.12 & 250.96.? (IAW = in association with ??)

If I understand your last statement correctly, the UL test to provide the listing for electrical conduit fittings (which means they are listed for grounding) is predicated upon Section 250.12 (Clean Surfaces for all grounding and all bonding for compliance) and Section 250.96 (bonding of other enclosures that are to serve as grounding conductors, which requires removing all nonconductive surfaces for compliance). If I understand this correctly: It seems the listing requirement for grounding and bonding of electrical fittings is predicated upon clean surfaces or removing nonconductive finishes from all contact surfaces to obtain clean surfaces. (For me the NEC language of 250.96: ?Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces? is all encompassing and would obviously include ALL contact surfaces.) If one side was sufficient for compliance it would say this in the White Book and in 250.96; and not send me to look for a study from 1992 which is not public knowledge?

If I combine this information with your previous statement, it seems that while ?serrations can cut through enamel paint to establish suitable bonding? (see UL document: Report of Research on Conduit Fitting Ground Fault Current Withstand Capability - 1992); this capability is not within their listing requirements for grounding. It seems as if you are saying that serrated locknuts can in fact peel paint, but they are not actually listed for that ? (I admit ? I am slow, and I am groping to understand this ? I am not attempting to speak for you, just trying understand what you have provided ?)

Section 110.3(B) mandates that ?Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling? and neither the NEC nor the UL White book seem to acknowledge the 1992 document you cite or your statement that ?serrations can cut through enamel paint to establish suitable bonding?. Fittings do not appear to be listed to peel paint (Is this correct or not ??).

Again, I mean no disrespect, I am honestly attempting to apply with everyday practicality, the information you have provided. Did I muck this up??

My biggest question is: Are any of your companies? (or is anybody?s) electrical fittings listed for grounding ?so as to make such removal unnecessary? ??

I am asking because I have been instructed otherwise. If you can provide additional clarification on this I would sincerely appreciate that.

mweaver

 

[mweaver]

Compliance with 110.3(B), 250.12 & 250.96

Compliance with 110.3(B), 250.12 & 250.96

Please pardon my response to my own post ... (after reflecting on my own post ...)

It seems to me that how each individual fitting manufacturer can respond to the question:


Are any of your companies’ electrical fittings listed for grounding “so as to make such removal unnecessary” ??


... will (simply and plainly) determine how we as installers, designers and enforcers maintain compliance with Section 250.12 and Section 250.96, and ultimately Section 110.3(B) [not to mention Section 250.97, as well] while utilizing their companies’ individual listed fittings ...

mweaver

 

[LJSMITH1]

Mweaver - No disrespect taken!

I appreciate your efforts to try and understand the issues surrounding these questions.

Let me see if I can clarify some of my comments further:

1.) Yes, the UL report is 'obscure' and possibly unavailable to the general public. It was a 'fact-finding' study, which UL occasionally conducts when they have received complaints from the field or other manufacturers when products don't seem to meet established specifications. In this case, UL wanted to see if the paint had any effect of how the bonding was established between the locknut and the enclosure. As another example of these fact-finding studies...

In 2002, UL received field complaints that listed EMT compression split ring type rain-tight fittings were permitting the entrance of water into the conduit system. After checking the validity of these claims - with a fact-finding study, UL made the decision to de-list ALL fitting manufacturers? compression type raintight connectors and couplings.

What this means is that some manufacturers may have claimed that serrations, nibs, or ridges on the locknuts would a) remove such coatings from enclosures, and b) provide the proper bonding to withstand the current tests. Unfortunately, none of this information was translated into the UL whitebook or NEC because not every manufacturer has 'serrations' on their locknuts.

2.) When UL created UL514B (and other electrical equipment specifications/requirements) together with industry, field, & manufacturers representatives, they took into account all of the NEC codes. With regards to UL514B, it was written in accordance with (IAW) NEC 250 as applicable to conduit and cable fittings. It is continuously revised to stay current with changing NEC, NEMA, NFPA or ASTM regulations.

3.) When we talk about "listing", many people have different interpretations of what that actually means. In short, "listing" means that the product meets the applicable standard that it was designed and manufactured for. Listing also means that the product is included on a qualified product 'list', validated by a third party (NRTL). The NRTL's responsibility is to periodically conduct verification tests/evaluations on the product to ensure it still meets the applicable standard. At anytime during an evaluation the product does not meet the established standards, it is 'delisted' and is no longer approved by the NRTL.

4.) In the same vein as #3, in order to be 'listed' for a purpose, it would need to be tested for such purpose. This is where we get into a grey area. If there is no specific test requirement to meet, there is no test required. In this case, there is no "paint/coating removal test" for locknuts or fittings in the governing specification UL514B. In actuality, UL514B does not specify painted or unpainted enclosures or boxes to use for its current tests. Therefore, they do not address preparation of said enclosure KO areas by sanding the paint or coating off.

To say that something is listed for a function of something that is not tested per the listing requirements, would be incorrect. The UL Whitebook combines the specification requirements with the NEC, and would not typically stray to define applications of products for which they were not designed - nor tested. In my experience, the Whitebook only covers the most likely applications of product.

Our company has never tested our locknuts on every type of enclosure coating out there, so we are not prepared to say our locknut does not require paint stripping around the KO in every case. However, UL did perform this test that involved a "standard" grey enamel-coated enclosure. Maybe, manufacturers who have a certain type of serrated locknut could state that they have a feature like the special serrations that don't require paint removal in "most" cases, but that might not mean much to anyone if it is not listed for that purpose - and here's where we revert into a circular argument with #4

So, it comes down to being better off removing the paint from the KO area to be sure you have a legit equipment bond - per the NEC direction. That way, you don't have to guess if your enclosure's coating is the .001" thick enamel, or is it a supertough epoxy.

Part of me wonders how many electricians actually strip the paint from every KO they fill with a fitting....

I hope I have clarified my thoughts a bit better than before.

 

[mweaver]

Your clarification brings this full circle

Your clarification brings this full circle

LJSmith1,

Thank you for responding with additional clarification on this issue. Your expanded explaination is extremely beneficial to me personally and (I am sure…) equally beneficial to others who review this thread.

This particular subject is an area of tremendous misunderstanding for installers, designers and enforcers alike. I, like many, have misunderstood the requirements surrounding this for most of my career (Hey… Nobody ever explained it to me… That’s, my only excuse…). The NEC requirements can be quite clear (well… at least on occasion …), but what actually must be accomplished in the field to maintain that compliance can be elusive to many, since in the field it all seems to turn into multiple shades of grey.... Truly understanding what it takes to maintain compliance is a process for most of us (I believe…). For me... The more I learn, the more I (obviously...) need to know …

I have been thinking that the 1992 study you cited reminds me of a study which was highlighted in both the 9th and 10th editions (Chapter eleven) of the IAEI publication: Soares Book on Grounding and Bonding. I am wondering now if it is one and the smae. I will have to check that possibility out. As I remember that chapter was quite interesting and it must be time to read it again, because I obviously don't remember enough about it ...

Your post has brought this full circle and to a close for me.


Although, I am imagining that most viewers of this thread do not want to read your statement:

“So, it comes down to being better off removing the paint from the KO area to be sure you have a legit equipment bond - per the NEC direction.”

I believe it did need to be said…


Regarding your closing thought:

“Part of me wonders how many electricians actually strip the paint from every KO they fill with a fitting....”

...While this needs no actual response... Since I have become more informed on this subject, I have wondered the exact same thing. I can only respond with another question: How many understand the need for this?

…Now, hopefully more understand… (Hey, it's a process...)

Thanks,
mweaver