Meyers Hub vs Sealing Locknut

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A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
When entering a Nema3 enclosure from the top, is a sealing locknut equally as good as a meyers hub for keeping things dry?
 

macmikeman

Senior Member
The answer depends on what type of raceway is intended to be installed into the fitting. I'll explain. Myers hubs are not listed to be used with emt. The threads are not tapered on emt fittings the same as rigid conduit. So in that regard, Yes.

I'll leave it to the others to answer the real question you are asking...
 

szrom

Member
Also would like to know...

Also would like to know...

I am an engineer, not an electrician and I would like to know the answer to this as well. We often specify grounding bushings on our conduit ends and I understand you cannot install a grounding bushing on a Myers hub.

An eletrician we worked with told us that Myers hubs are the only acceptable water-tight fitting. I would appreciate it if someone could confirm this.

Thanks.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Last edited:

hurk27

Senior Member
Without a seal between the fitting and the top of a cabinet I do not see how an "O" ring on a locknut will seal? water will still go through the threads, Arlington Industries does have UL listed sealing washers that work for PVC male adapters, not sure about EMT fittings.
 

tom baker

First Chief Moderator
Staff member
I am an engineer, not an electrician and I would like to know the answer to this as well. We often specify grounding bushings on our conduit ends and I understand you cannot install a grounding bushing on a Myers hub.

An eletrician we worked with told us that Myers hubs are the only acceptable water-tight fitting. I would appreciate it if someone could confirm this.

Thanks.

Meyers (trade name) makes a grounding nut for that application.
Your electrican is wrong. Product application is determined by the listing and the listing instructions. Listing information from UL is available in the UL white book, which is now interactive, IE a section in the NEC leads to the specs in the white book. The UL white book is full of usefull information.

And here is an electrical instructors tip for you. When an electrican says "The only..." he is usually wrong. Many have a habit of learning how to do something and it may be wrong, or the code changes. I have learned to question, or say I don't know, as you do. Thanks for using the forum.

For installations, I will use sealing locknuts inside for wet or dirty enviroment. Outside I would be more likely to use a meyers, esp on the top.
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
Without a seal between the fitting and the top of a cabinet I do not see how an "O" ring on a locknut will seal? water will still go through the threads, Arlington Industries does have UL listed sealing washers that work for PVC male adapters, not sure about EMT fittings.

Hurk, it sounds like the Arlingtons' product contradicts your first sentance. I am using PVC so it sounds like a Meyers Hub and a Male Adapter is out because of the thread difference. The sealing locknut seems like a good choice. BTW, if the sealing lock nut is tight, I don't see how water could get past it. I just want to be sure it is legal........
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
For installations, I will use sealing locknuts inside for wet or dirty enviroment. Outside I would be more likely to use a meyers, esp on the top.

Tom.....but what about the thread difference between MA's and EMT fittings VS rigid pipe or do PVC MA's have the correct threads?
 

hurk27

Senior Member
Hurk, it sounds like the Arlingtons' product contradicts your first sentance. I am using PVC so it sounds like a Meyers Hub and a Male Adapter is out because of the thread difference. The sealing locknut seems like a good choice. BTW, if the sealing lock nut is tight, I don't see how water could get past it. I just want to be sure it is legal........

No, the Arlington sealing washer is places on the fitting before you put it into the hole, it seals between the fitting and cabinet outside of the threads, if placed it inside the cabinet it cant seal because of the threads.
 

Mgraw

Senior Member
Location
Opelousas, Louisiana
Occupation
Electrician
Sealing locknuts seal around the threads. I haven't had one leak yet. The only "issue" is they need to be centered in the knockout to seal really well. PVC fittings have pipe threads like RMC.
 

dicklaxt

Senior Member
I have specified Myer's Hubs for many years for use with rigid(not sure about IMC & EMT) in classified industrial complexes.They do make a grounding hub,,,,,,,,Scru-tite series ,they are rated NEMA 4 which covers hose directed water.We never were allowed to enter the top of any outdoor box in any scenario.

dick
 

kwired

Electron manager
Location
NE Nebraska
The answer depends on what type of raceway is intended to be installed into the fitting. I'll explain. Myers hubs are not listed to be used with emt. The threads are not tapered on emt fittings the same as rigid conduit. So in that regard, Yes.

I'll leave it to the others to answer the real question you are asking...

Without a seal between the fitting and the top of a cabinet I do not see how an "O" ring on a locknut will seal? water will still go through the threads, Arlington Industries does have UL listed sealing washers that work for PVC male adapters, not sure about EMT fittings.

A listed raintight EMT fitting comes with a gasket or O ring that must be installed for the fitting to meet the listing. There are some out there that are plain crap and are hard to keep from separating from the connector and there are others that work great.
 

Smart $

Esteemed Member
Location
Ohio
Hurk, it sounds like the Arlingtons' product contradicts your first sentance. I am using PVC so it sounds like a Meyers Hub and a Male Adapter is out because of the thread difference. The sealing locknut seems like a good choice. BTW, if the sealing lock nut is tight, I don't see how water could get past it. I just want to be sure it is legal........
Excerpt from UL: DWTT.GuideInfo, Conduit Fittings


Sealing (Liquid-tight) Locknuts ? Sealing locknuts are intended for use with threaded rigid metal conduit and intermediate metal conduit with one sealing locknut in the outside or the inside and either an ordinary locknut or sealing locknut on the inside of the enclosure for wet locations or liquid-tight applications. Sealing locknuts may also be used with Listed wet location or liquid-tight fittings where so marked on the fitting carton and used on the inside of the enclosure.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I generally try to avoid coming in the top of any outdoor enclosure. A Meyers type hub works a bunch better then a locknut and sealing washer(s), but putting the conduit entry on the side or bottom works even better.

I have seen a fair number of conduits attached to boxes with just a double locknut that have come loose over time, with or without sealing washer(s), so I generally discourage that practice as much as I can.
 

iwire

Moderator
Staff member
Location
Massachusetts
Rigid PVC is not threaded (as I am sure you know:)) as has been mentioned connectors have straight threads and will not seal into a Myers hub
 
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