General-purpose enclosure with 220 V in Class I, Division 2 location - possible?

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Hi all.

I just beginned study NEC and have a lot of questions. I hope I will be modest enough not to annoy you too much, but there is one question which is really interesting for me.

Consider an usual Class I, Division 2 location ? for example, pump room with normally adequate ventilation, but which may failure.
NEC says 501.115(B)(1):
"Type required.
...
unless general-purpose enclosures are provided and any of the following apply:
and exception (4):
?The device is a solid state, switching control without contacts, where the surface temperature does not exceed 80 percent of the autoignition temperature in degrees Celsius of the gas or vapor involved.?

So, according to it, can I use general-purpose enclosure (maybe IP68) for solid state power contactor, even if it will control AC 220 V circuit?
It is absolutely unthinkable in our practice, in Russia. Dangerous location with 220 V (or any not-nonincendive circuit) ? is Exd and only Exd, without variants.

Does anybody does different? Or do I misunderstand NEC?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
You seem to be mixing IEC requirements and NEC requirements together. That may be part of why what you are ending up with is giving you some concern.

Class 1, division 2 areas are not normally hazardous at all. They only become hazardous during uncommon events. The protection scheme eliminates the most common potential sources of ignition (such as arcing or sparking contacts) by enhanced protection such as explosion proof enclosures, but things that are unlikely to produce ignition require no further protection.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
One of the general distinctives between IEC and NEC is there is so such thing as "general purpose" applications in IEC classified locations. An "Increased Safety" protection technique (Type "Ex e") is basically the minimum. That said, even in Russia, voltage levels are not a typical basis for evaluating protection techniques except for some nonincendive or intrinsically safe applications.
 
What is "General-purpose enclosure"?

What is "General-purpose enclosure"?

I carefully read IEC 60079-7 about type "Ex e". There are a lot of requirements, and Exe equipment must meet them. So, can it be "general-purpose enclosure"? I think no. But - what NEC writes about?
There is a mention about Ex e
protection technique in NEC, so, if NEC means Exe - it must point it out clearly?
Where can I read more about it? I see there is a big misunderstanding :-(
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I carefully read IEC 60079-7 about type "Ex e". There are a lot of requirements, and Exe equipment must meet them. So, can it be "general-purpose enclosure"? I think no. But - what NEC writes about?
There is a mention about Ex e
protection technique in NEC, so, if NEC means Exe - it must point it out clearly?
Where can I read more about it? I see there is a big misunderstanding :-(
It is confusing. It is also important to understand that a recognized protection technique in the NEC is not necessarily a required protection technique. We had a similar discussion here.

NEC and IEC "Zone" concepts, while moderately related are NOT the same. I co-authored a paper in the mid-nineties that may help a bit. It is very dated now; the ATEX Directive had just been instituted and several other developments have occurred since, but it is still a start and many comparisons are still valid.

One thing to consider, ANSI/ISA 60079-7 and ANSI/UL 60079-7 which are referenced in Informational Notes in NEC Article 505, Section 505.2 are only somewhat related to IEC 60079-7 which is not directly referenced in the NEC. ANSI/ISA 60079-7 and ANSI/UL 60079-7 have been heavily "Americanized" to reflect greater a affinity for NEC Division concepts than IEC Zones. One example: NEC Zone equipment must be marked "AEx" to reflect certain testing that IEC 60079-7 doesn't require. "Ex" or 'EEx" is not acceptable

I don't intend to create an exhaustive comparison of the current relationships between NEC and IEC Zones. I will say every US domestic manufactures' poster I've seen is inadequate except to compare NEC Divisions and Zones.
 
AM
rbalex, thank you for the link, it was really interesting. I am from Russia, and we are harmonizing our stantarts with IEC. Can you please point me out where can I found a more comprehensive and contemporary materials about the difference between NEC and IEC in terms of hazardous locations? I am also interesting in the procedures of determining the size of the dangerous zone in the different countries and by different standarts. What is a best practices or standarts about it?
 
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