Type X Purge for Class 1 Division 1

Status
Not open for further replies.

fifty60

Senior Member
Location
USA
Is type X purging an acceptable protection technique on an individual electrical enclosure inside of a class 1 division 1 location? Or, is type X purging meant to be applied to the entire room? Would type X purging used on a sub panel enclosure allow for unclassified components to be used inside the enclosure?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is type X purging an acceptable protection technique on an individual electrical enclosure inside of a class 1 division 1 location? Or, is type X purging meant to be applied to the entire room? Would type X purging used on a sub panel enclosure allow for unclassified components to be used inside the enclosure?

A type X purge is used to create a non-hazardous space inside of an enclosure of some sort that would otherwise be CID1.

A similar idea is often applied to entire rooms.

The whole idea is to create a volume of space where normal components can be used.

Best bet is to buy such a system (already UL listed) rather than trying to make it yourself, as there are some nuances that are best left to people more familiar with the requirements. Then you can just attach it to your UL 508a listed industrial control panel and create an unclassified space inside your enclosure.

I will point out that this is an unpopular technique in some plants.
 

fifty60

Senior Member
Location
USA
Is it normal to purchase the enclosure and purge system in one assembly? Or, would I look to only purchase the purge system to use with any basic Hoffman enclosure?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is it normal to purchase the enclosure and purge system in one assembly? Or, would I look to only purchase the purge system to use with any basic Hoffman enclosure?

You would normally buy the UL listed type X system separately from whatever it is you are trying to make unclassified.

My understanding is that generally, there are no special requirements for the enclosure being pressurized, either for the enclosure itself or what is in it.

I have heard that there are some places that will only allow this technique on UL listed devices such as UL508a control panels, but I don't believe that is a basic requirement. It may be a plant thing, or some kind of local practice.

There are some devices this technique is unsuitable for such as certain displays with touchscreens or membrane keypads mounted through a door. Some of them do not deal well with having higher pressure behind them.
 

fifty60

Senior Member
Location
USA
Reading NFPA 496, I do not see any requirements for a specific NEMA style enclosure. I have been told by technical support for type X purge suppliers that I should use a NEMA type 4.

The enclosure I have is Type 4, 12. Does Type 4,12 basically mean NEMA type 4, but built with no knockouts like a type 12?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Reading NFPA 496, I do not see any requirements for a specific NEMA style enclosure. I have been told by technical support for type X purge suppliers that I should use a NEMA type 4.

The enclosure I have is Type 4, 12. Does Type 4,12 basically mean NEMA type 4, but built with no knockouts like a type 12?
If it is marked NEMA 4/12 that means it meets the requirements for both types. I have never seen a NEMA 4 with knockouts.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Reading NFPA 496, I do not see any requirements for a specific NEMA style enclosure. I have been told by technical support for type X purge suppliers that I should use a NEMA type 4.

The enclosure I have is Type 4, 12. Does Type 4,12 basically mean NEMA type 4, but built with no knockouts like a type 12?

type 4 or 4X are usually used with pressurization systems because they can take the internal pressure better so they leak less air. air is a very expensive utility in plants.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
type 4 or 4X are usually used with pressurization systems because they can take the internal pressure better so they leak less air. air is a very expensive utility in plants.
I wonder if that is still true? In past years, all of the type 4 enclosures had door clips on three sides. In fact, that was often the only difference between a type 4 and a type 12...the 4 had clips on 3 sides and the 12 only on the side opposite the hinge.

Now I see a lot of the type 4 enclosures with clips only on the side opposite the hinge.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I wonder if that is still true? In past years, all of the type 4 enclosures had door clips on three sides. In fact, that was often the only difference between a type 4 and a type 12...the 4 had clips on 3 sides and the 12 only on the side opposite the hinge.

Now I see a lot of the type 4 enclosures with clips only on the side opposite the hinge.

IIRC, the UL std for type 4 boxes requires a higher clamping pressure than for type 12. How they meet it is up to the designer.
 
Status
Not open for further replies.
Top