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Old January 28th, 2017, 01:35 PM   #1
RRoc
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Nema 7 Classification Help

I have a control station that just has two selector switches on it in a Class 1 Div 2 Area. I'm providing for this control station a Stainless Steel Nema 4X enclosure and a Cutler and Hammer Selector switch that is rated for Class 1 Div 2 area. The Selector switch contacts are Hermetically Sealed.

My specification is calling for a Nema 4x and Nema 7 enclosure. Do I have a case to state that a Nema 4X enclosure with the hemertically sealed contacts does not need a Nema 7 enclosure rating?

RRoc

Last edited by RRoc; January 28th, 2017 at 01:50 PM.
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Old January 28th, 2017, 02:18 PM   #2
jraef
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Yes you have a case. The risk is, some day someone may replace one of those contact blocks with the non-hermetically sealed versions, whereas with a NEMA 7 enclosure, that would not matter. So it depends a lot on the professional integrity of the user; i.e. do they take things like this seriously, or are they populated by grunts who just "get 'er done". If it's someplace like a refinery, they generally know the score but if it's a Cl1 Div 2 environment in a gas station, I would not trust it.
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Old January 28th, 2017, 02:31 PM   #3
jkerekes
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I'm not sure about the hermetically sealed contacts also. You have no way to know if somehow the sealing fails.
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Old January 28th, 2017, 03:12 PM   #4
diat150
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Quote:
Originally Posted by jkerekes View Post
I'm not sure about the hermetically sealed contacts also. You have no way to know if somehow the sealing fails.

Im not a true expert on this, but I dont think that is how it works. If it is a class 1 div 2 area you use class 1 div 2 components. You dont worry about if something fails.
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Old January 28th, 2017, 07:22 PM   #5
jkerekes
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I think your correct technically. They are allowed. But they are still impossible to verify.
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Old January 28th, 2017, 09:30 PM   #6
James Mcquade
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Since you have only 2 switches,

you may want to consider buying an ab 800h box and 2 of their switches
its a nema 7 enclosure and so are the switches. Use rigid conduit all the way back to the non hazardous area and use seal offs. I don't think barriers will be required.

this is what we did in a class 1 div 1 environment.

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Old January 29th, 2017, 10:57 AM   #7
jraef
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Assuming from the description that you are using contact elements that are UL listed as Class 1 Division 2, as are offered by most of the major mfrs, the concept of using them in a standard NEMA 4 enclosure as opposed to a NEMA 7 enclosure when they are the ONLY elements in the box, such as a control station like yours, is the EXACT intended use that they are listed for. Failure risk is already part of the process of being listed by UL.

My point was the future risk based on the kind of end user environment: conscientious industrial facility with rules and training, or casual user who may bring in untrained unqualified people to fix things who do not understand the risks of using the wrong components. If you use the NEMA 7 route, standard pilot devices can't be mounted in them but the rating of the contact blocks inside becomes irrelevant. It essentially forces them to use the right parts. If it's a refinery or processing facility however, that's typically not much of a risk.
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Old January 29th, 2017, 04:44 PM   #8
James Mcquade
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One thing you MUST remember.
NEC70 rules state that no device can be use in an environment unless it is listed for that use.
When in a classified area, you must adhere to the hazardous section of the code - the 500's

you must also look at the rules regarding purging / pressurizing enclosures since it is a nema 4 enclosure.

While using sealed contacts may be allowed(i'm not convinced you can), you still have to have safety barriers and seal offs to prevent wiring shorts, replacing the contacts with non sealed ones, and open space back to the control panel and creating a hazard.

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