Use of Bonding Jumper in Class II, Division 1 Locations

[powergage]

We recently performed a full evaluation of our Class II, Division 1 classified locations (coal handling). There were several instances in one building where single locknuts were used for conduit penetrations in enclosures.

What can we do to meet the Code requirements for these conduits/enclosures?

Is there a "quick fix" that can be retrofitted to the system?

Can we redo the penetrations with Myers Hubs?

Can we install external bonding jumpers to meet the Code requirements? There is a note in the 2008 Handbook under 502.12(B)(4) that states "Standard pressed-steel boxes that are not identified for Class II locations are permitted as long as they do not contain taps, joints, or terminal connections, are dusttight, and ARE PROVIDED WITH A BONDING JUMPER AROUND THE BOX IN ORDER TO COMPENSATE FOR THE ABSENCE OF THREADED HUBS." I know this is under the Class II, Div 2 section, but does this apply to Class II, Div 1 areas also? If so, this would save a tremendous amount of time and money?

Thanks!

 

[resqcapt19]

502.10(A)(1)(4) requires the use of boxes with threaded hubs for a Division 1 location. In my opinion, even the use of a "Myers hub" does not meet the requirements of this section.

(4) Fittings and boxes shall be provided with threaded bosses for connection to conduit or cable terminations and shall be dusttight. Fittings and boxes in which taps, joints, or terminal connections are made, or that are used in Group E locations, shall be identified for Class II locations.[/quote

 

[powergage]

Thanks, resqcapt19. Does anybody else have an opinion on Myers hubs? I looked up Myers hubs on Cooper Crouse-Hinds' website and the data sheet lists "Class II, Divison 1 & 2" under the 'Certifications' section.

 

[rbalex]

Resqcapt19’s answer is correct and is the only clearly NEC compliant solution. Crouse-Hinds has had a long history of suggesting their products are “compliant” for a particular application, (and they very likely are) but the products are not necessarily listed for it – they may not even be listed at all. In this case though, Myers-Hubs are both listed and depending on the model, listed for grounding as well, but not necessarily Class II nor bonding.

The critical issue is bonding such that absolutely no stray, harmonic nor fault current can produce an arc at any joint. This is particularly critical for Division 1. See 502.30(A). Note the Section applies equally to both Divisions 1 & 2. While fault currents may be rare, stray and harmonics may occur anytime and thus the Section applies to Division 2.

You might consider approaching an alternate solution through Section 500.8(A). The key is the term identified. It is defined in Article 100. The associated Fine Print Note implies identified means listed or labeled. It doesn’t. That is why Code Making Panel 14 wrote Section 500.8(A) for classified location applications. Many products that are suitable for classified locations are not specifically listed or labeled for them. If you can assure yourself that the bonding methods used can prevent any arcs at joints, then 500.8(A)(3) may be your answer.

 

[powergage]

Veeeerrryyy interesting. That can be a pretty big judgment call for the Authority Having Jurisdiction, especially if the AHJ isn't exactly a Code expert.

That leads to an interesting question, if a threaded Myers hub doesn't meet the "threaded" requirement, what does?? Again, I'm talking about the case where a box does not contain aplices, terminals, etc. Is there such a thing as a dust tight enclosure with threaded inlets that isn't explosion proof??

Also, if we wanted to wanted to meet the intent of the Code, but without spending thousands of dollars to change out a simple locknut, could we just add bonding wedges (e.g. T&B series 3650) to the locknuts and run a bonding jumper to a ground lug in the enclosure??

I know it sounds like I'm trying to be cheap, but we're talking about hundreds of man-hours just to fix a single box if we have to pull out all of the wires and redo all of the penetrations.

 

[rbalex]

While most NEMA manufacturers in the classified location enclosures industry make combined Type 7/9, Adalet and Hoffman both have Type 7 "only" available. I've never used either one in a Class II location, but both are reputable companies. Hoffman doesn't make Type 9 enclosures at all.

I didn't say Myers Hubs aren't suitable, I said they aren't UL listed for Class II. They are however, CSA Certified for Class II, both Divisions 1 & 2. In this particular case, CSA is not a NRTL because the certification is not based on an ANSI or ASTM standard.

I have no problem with cheap (well, cost-effective that is), I do have an issue with safety. I have outlined the critical issue. If you believe you can make your case with bonding wedges to the AHJ, go for it - although I would prefer you made it with your insurance underwriter.

 

[powergage]

Thanks, rbalex. I tend to agree with your approach. I am generally very conservative by nature on these types of issues. Just trying to play "devil's advocate" and explore all options.

Any other guidance is fully appreciated! Thanks!

 

[resqcapt19]

Bob,
I sais Myers hubs are not suitable based on the code language. The code requires that the enclosure itself have a threaded boss when installed in a Class II, Division 1 area. My reading of 502.10(A)(1)(4) says that the "theaded boss" has to be a part of the enclosure, not an add on fitting like a Myers hub.

 

[powergage]

respcapt19-
The reference to "threaded bosses" makes sense in the case of conduit fittings; I think all conduit fittings (e.g. outlet bodies, etc.) rated for hazardous locations have threaded entrances cast right in. However, in the case of enclosures, they typically don't have the same pre-fabbed entrances. You typically have to drill and tap them for your conduit penetration.

For the case where no splice is present and you just need the enclosure to be dust tight, a standard dust tight enclosure will not be thick enough to drill, tap, and thread your rigid conduit right into it. So what are your options if you can't use a threaded hub instead??

 

[rbalex]

Don,

I agree Myers Hubs will not meet the literal text. The boss must be integral to the enclosure.

The question became whether Myers Hubs can be used in an alternate method to meet the actual need of the installation. The installation must be acceptable to the AHJ and the AHJ must be able to identify their suitability. They aren't listed; so some other option, if available, under 500.8(A) needs to be used. I only see 500.8(A)(3) as the only viable option.

Note the three 500.8(A)options are a summary on FedOSHA's definition of acceptable in 29 CFR 1910.399.

So, far I haven't said the Myers Hubs are acceptable, I simply haven't counted them (or any other option) out either. I have stated from the beginning, yours was the only immediately defensible interpretation.

 

[resqcapt19]

powergage,
The code section that I cited clearly applies to both fittings and boxes in the Class II, Division 1 location.

...(4) Fittings and boxes shall be provided with threaded bosses for connection to conduit or cable terminations ...

In a Class II location, I can see the Meyers hub doing the job that is required, but I just don't see it as being code compliant. Maybe the code needs to be changed. The wording in 501.10(A)(3)for Class I, Division 1 locations seems less restrictive.

(3) Boxes and Fittings. All boxes and fittings shall be approved for Class I, Division 1.

 

[powergage]

I agree with the Code language change. It's an issue of Code language versus reality. They try to give you some leeway if there's no splice in the box by saying that it only has to be dust tight, but then they say it still has to have threaded bosses. No such enclosure exists in the real world.....except one that is rated explosion proof, so you're right back where you started.

I think rbalex's approach of utilizing 500.8(A) is the only way to 'get around' not having all explosion-proof enclosures regardless of what's inside.

 

[rbalex]

How would you revise the Code? Technically, explosionproof won't do the job either. See Section 502.5.

Don (resqcapt19) and I are both familiar with how to make Proposals to revise tne NEC; both of us have even been successful a few times.

I would suggest revising the text of 502.10 (A)(4) to read something like:

Fittings and boxes shall be provided with threaded bosses or threaded hubs listed for grounding and bonding for connection to conduit or cable terminations [and]; the assembled enclosure shall be dusttight.

The text in [brackets] would be deleted and the underlined text added.

 

[Thealanator]

I think this is why the code is fussy about threaded connections, integral bosses, etc.

The idea is to keep an internal explosion from propagating to the exterior of the enclosure. Hot gases are cooled as they pass through the small openings provided by the threaded connection. Finely machined flanges on bolted enclosures accomplish the same thing.

A conduit penetration held with a locknut implies an enclosure that is not explosionproof. If this is a Division 1 area, the enclosure/installation appears to be out of compliance.

 

[resqcapt19]

Thealanator,
The code does not require that enclosures for Class II installations be able to contain an explosion like is required for Class I installations. The idea for Class II is only to prevent the dust from getting into the enclosure. It is easier to prevent dust from getting into an enclosure than it is to prevent vapors from getting into the enclosure.

The idea for Class I is that you cannon prevent the flammable vapors from entering the enclosure and the enclosure must be able to, as you said, cool the hot gasses when the explosion occurs.

 

[powergage]

rbalex-

I think it would be best to split 502.10(A)(4) into two sections:

(4) Fittings and boxes:
(a) Fittings and boxes in which taps, joints, or terminal connections are made, or that are used in Group E locations, shall be identified for Class II locations. They shall be dusttight and be provided with threaded bosses for connection to conduit or cable terminations.

(b) Fittings and boxes that do not contain taps, joints, or terminal locations shall be dusttight. They shall be provided with threaded bosses or installed with threaded hubs listed for grounding and bonding for connection to conduit or cable terminations.

 

[rbalex]

See:

http://www.nfpa.org/categoryList.asp?categoryID=124&URL=Codes & Standards

Look on the right-hand side for the NEC Proposal Form. The download is MSWord format. You have until 5pm, EST, Nov 4, 2011 to get it in.
Work every angle in the Substantiation. If you make your Proposal and it isn't Accepted, I'll support it during the Comment stage.

 

[BJC]

If your coal handling area is part of a power plant the NEC does not apply- use the Meyers hubs.

 

[rbalex]

If your coal handling area is part of a power plant the NEC does not apply...

But the NESC probably does. While I agree the NEC is overkill in this particular case, you might want to review NESC Rule 126.

 

[powergage]

...you might want to review NESC Rule 126.

Section 127 of my 2007 NESC states the following:

Electrical installations in classified areas shall meet the requirements of the NEC, Articles 500 through 517. Areas classified in accordance with NEC Article 500 shall comply with the requirements of that Article and A. through L. below. Areas classified with the optional Zone method in accordance with NEC Article 505 shall comply with the requirements of that article.