501.10(A)(3) C1D1 Boxes and Fittings

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lpfink

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2014 NEC referenced here:

501.10(A)(3) states that "All boxes and fittings shall be approved for Class 1, Division 1". I am assuming explosionproof is my approved enclosure.

501.15(A) excludes explosionproof enclosures with entries less than 2" containing only terminals, splices or taps, to be sealed.

So I'm not sealing my 1.5" hub size explosionproof enclosure containing these non arcing, sparking or heat producing components.

My questions are:

1) Is there a need for an explosion proof enclosure in this scenario?

2) Is there anytime that a Class 1 Division 1 approved enclosure would not be used in a Class 1 Division 1 location?

Thank you!
 
Section 501.15(A)(2) is only addressing omitting seals, not enclosures.

1) Not necessarily, but it still needs to be approved for Class I, Division 1. Section 500.7 lists some other protection techniques that may be suitable.

2) An enclosure approved for Class I, Division 1 may be used in other environments; however, it must also be suitable for the environment. That is, a Type 7 enclosure is only suitable for indoor installations unless it is also identified for outdoor installations. It may also need to be corrosion resistent.
 
Bob,

I understand your response and thank you! Follow up questions are:

1) If you do choose to meet 501.10(A)(3)) by using an explosion proof enclosure with these non arcing, sparking or heat producing components, and do not seal it, what's the point? I guess I'm wondering why this requirement doesn't have exceptions for components not in danger of igniting the Class 1 Division 1 atmosphere, or is there always a possibility of these types of components igniting the atmosphere?

2) Off topic a little but I read 501.15(B)(2) last sentence that states "Such seals shall not be required to be explosionproof but shall be identified for the purpose of minimizing the passage of gases permitted under normal operating conditions and shall be accessible." Are there a multitude of conduit seals available that aren't explosion proof but identified for these purposes of minimizing passage of gases? or do most use a seal serving both purposes?

My company use to use conduit to wire our equipment but have now moved toward cable. I still need to support the earlier projects as many of the customers want to stick with conduit for upgrades and refurbishments. Thanks again for the help!
 
Hey lpfink and Bob,

I'm jumping in here because I am chasing down answers for similar questions, but I can offer a bit of experience I have dealing with product design using non-arcing/non-sparking components - these are non-arcing/non-sparking during normal operation, but they would pose a problem in the event of a failure in a Division 1 location. From my experience, this is OKAY in Division 2 because you aren't assumed to have an explosive atmosphere at all times, whereas in Division 1 you are assumed to always have said atmosphere. In the Division 1 case, the "first failure" is of the non-arcing component and causes a hazard because the explosive atmosphere is assumed. In the Division 2 case, the "first failure" would be the presence of the explosive atmosphere to begin with, hence the general use of non-arcing/non-sparking stuff being sufficient as a protection method. This would be different if the component were say Intrinsically Safe, because in that case even a component failure would not cause a hazard.

So for your C1/D1 scenario, you would have to put the non-arcing/non-sparking bits into a suitable enclosure for the Division 1 space, and then meet the Division 1 sealing requirements based on your specific installation (trade size, distances, etc.).

Your reference to the line in 501.15(B)(2) would apply if you were Class 1 Division 2. From what I know, there are specific pack & pour style sealing fittings for entering boxes in Division 1 locations and/or leaving Division 1 locations with a conduit to an unclassified space. My read of (B)(2) would be that you don't need these (large, bulky) specifically listed explosion proof sealing fittings for leaving a Division 2 location and instead you can use some kind of fitting normally used to prevent the transmission of vapor - the point there is to prevent your unclassified location from becoming classified (because in the event of a failure, aka flammable atmosphere, in the Division 2 location it would just migrate therefore making your unclassified location actually Division 2). This is how we handled it on many power gen systems we had running off natural gas, propane, hydrogen, etc. The idea is to create some kind of vapor boundary to keep the unclassified locations as such, but not to the level of needing to contain an explosion as in the case of a Division 1 space.

This is from my experience - I've been lurking on these forums for a while and never had occasion to post, but from my reading over some time I would say if Bob says different then I would go with his advice and not mine. I'm still a little wet behind the ears at 10 years in my electromechanical design seat :)

I have some additional questions about the requirements of the explosion proof sealing fittings in C1/D1 spaces, for which I will post another thread (when my newbie permissions go through...)
 
Grockj,

Thank you very much for the reply! Is there some reading of "failures" you could recommend or is that just common sense? I'm wondering if understanding that would be another tool in helping me to understand proper hazardous location design?

I've been reading these forums about sealing at a boundary from Class 1 Division 2 to unclassified location, and I've seen a lot saying that there aren't many times its necessary but nothing describing those times it is. On a piece of enclosed equipment where the interior is classified as a Class 1 Division 2 and the exterior could be a Class 1 Division 2 or non-haz, I guess it is safer to standardize on non-haz, especially if there is a device needing sealing close to the boundary. I would think the seal could serve both purposes, seal the device and for boundary seal. Have you any thoughts on this?

Talking about wet behind the ears, I've only been here in my company since 2014.:)
 
I'm sorry, I've had a rough week. The last two posts are just too complex for me to get a clear idea of the situation at the moment.

I will say, there appears to be a misconception with the idea of "first failure". See Section 500.5(B)(1)(3). There is no "first failure"; the failure and ignition source must be caused simultaneously.
 
Hi Bob,

Hope your week gets better!!

Thank you and I'll go over section 500.5(B)(1)(3).

Did you see my reply to your first response? I have a couple of follow up questions. I thought you could help to mitigate some of my confusion! Thanks again!

Loren
 
lpfink said:
Bob,

I understand your response and thank you! Follow up questions are:

1) If you do choose to meet 501.10(A)(3)) by using an explosion proof enclosure with these non arcing, sparking or heat producing components, and do not seal it, what's the point? I guess I'm wondering why this requirement doesn't have exceptions for components not in danger of igniting the Class 1 Division 1 atmosphere, or is there always a possibility of these types of components igniting the atmosphere?

2) Off topic a little but I read 501.15(B)(2) last sentence that states "Such seals shall not be required to be explosionproof but shall be identified for the purpose of minimizing the passage of gases permitted under normal operating conditions and shall be accessible." Are there a multitude of conduit seals available that aren't explosion proof but identified for these purposes of minimizing passage of gases? or do most use a seal serving both purposes?

My company use to use conduit to wire our equipment but have now moved toward cable. I still need to support the earlier projects as many of the customers want to stick with conduit for upgrades and refurbishments. Thanks again for the help!
Click to expand...
Let's start with the "fire triangle". For practical purposes we need air, fuel and a source of ignition. For the nitpickers we are talking about practical purposes. Hazardous locations assume air is always available for all Classes and Divisions. Division 1 assumes that fuel will be available at the time an ignition source becomes available. Division 2 assumes ignition sources occur under the equipment involved's design operating conditions but fuel is not available under design operating conditions. Catastrophic releases of fuel are not considered under general electrical area classification criteria. NFPA/API have determined that a catastrophic release of fuel will be ignited by something electrical or not.

1) Since fuel is assumed to be available in Division 1, either under standard operating conditions or concurrently with a non-design potential source of ignition (e.g., a short) under non-catastrophic system failure, the protection techniques [Section 500.7] must be suitable [Section 500.8(A)] to prevent ignition of the surrounding atmosphere. Explosionproof enclosures would not be expected to contain an explosion frequently where it only contained non-arcing, non-sparking or non-high temperature components. However, where entrances to the enclosure is 2 inches or larger, common experience anticipates a sufficient increase in available fuel and warrants sealing the enclosure.

2) If a seal is listed it will be explosionproof. Study the terms identified in Article 100 and suitable in Section 500.8(A). non-explosionproof seals are " identified.
 
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