Class 1 Div 1

[rswolff001]

Understand difference between C1D1 and C1D2. Have seen many offerings for C1D1 pc's and HMI's where the unit is mounted in an XP enclosure, however the touchscreen is accessible to an operator. Would mounting a unit rated for a C1D2 environment into a purged panel (instead of an XP one) still comply with C1D1? I've seen instances where its done, but in speaking to many people some say no, some say yes, and basically no one is actually sure. I'm not sure why mounting in an XP enclosure would be necessary as the device is not 'contained' in the enclosure but protrudes through it. Hard to contain an explosion that way.:-?

 

[rbalex]

Yes, done properly, it could work. In fact, if you wouldn't mind the potential hassles of a possible shutdown from loss of pressure, you might be able to use "ordinary location" equipment. See NFPA 496; especially Chapter 5.

 

[bobgorno]

I cheated and copied this from an old posting of mine. It should all still apply except the references may be old.

Devices protruding thru the enclosure - Logically one wants to make them acceptable for the area classification that they are exposed to. If the enclosure is unclassified inside, the enclosure wall is the boundary and the area outside of it is hazardous. There is no magic force field that envleopes the protruding devices.

Review the commentary in the NEC Handbook following 500.7(D). Key words "within the enclosure"

Review the definitions in NFPA 496 for pressurization types. Key words "within the protected enclosure?

The following are excerpts from ISA-RP12.4-1996 (Note this is outdated and I recommend purchasing the newer version):
?Chapter 6 - Components that protrude through the enclosure? ?Components should permit the flow of the protective gas to properly purge and pressurize the component. (Additional information is located in Annex B.) Exception: components that are suitable for the hazardous location that would exist in the absence of the protective gas do not require purging or pressurization? ?Annex B, 6 ? This requirement is intended for components such as switches, keyboards, lamps, indicators, and for mechanical devices such as shafts that penetrate the enclosure. Methods of protection to comply with the exception include mounting the component in an explosion proof housing or using the component in an intrinsically safe circuit??

From P&F BEBCO EPS, Purging Technology Review:
The use of devices that penetrate the surface of a protected
enclosure must be carefully scrutinized. Protruding devices
will likely contain electrical components that could either be
exposed to the hazardous location or be isolated from the
fl ow of protective gas. Conventional wisdom suggests that a
protruding device should be acceptable if it is (1) explosion
proof, (2) intrinsically safe, (3) proven to emit insufficient energy
to ignite the surrounding atmosphere (applicable for Division 2
locations only), (4) constructed so that all electronics within its
face are suitably sealed from the surrounding environment and
properly ventilated to the protected enclosure, or (5) isolated
from the surrounding atmosphere by a sealed window or access
door that is properly ventilated to the protected enclosure.
Controllers, Indicators & Recorders
Today's panel mounted instrumentation is almost strictly
electronic. The protruding face of these instruments normally
contains LEDs, LCDs and incandescent or fl orescent lights.
Therefore, it is extremely important to isolate all instrumentation
from the surrounding atmosphere, unless the face is sealed
and all electronics are properly ventilated to the protected
enclosure.

 

[rswolff001]

ok, understand this and that. but still not getting a grip.

I have seen offerings for devices, such as touchscreens, where the device is in an XP enclosure, but the touchscreen is still open to the environment. How would this differ from mounting in a purged enclosure? This presumes the protruding part of the device is sealed against the atmosphere penetrating through the device into either itself, or the enclosure.

Same goes for NEMA4 rated pb's, or indicators? If they are sealed from the atmosphere, would it be suitable (legal) to mount these in a purged enclosure in a Class 1 Div 1 area?:-?

 

[rswolff001]

still not sure if I get it.....so if my purged enclosure is in the C1D1 area, and I put a sealed push button into the door, is that ok? If the sealed push button is illuminated (LED) is that ok? how about an operator touchscreen where the exposed part of the device is sealed from intrusion either into the device or the enclosure....is that acceptable?

 

[weressl]

ok, understand this and that. but still not getting a grip.

I have seen offerings for devices, such as touchscreens, where the device is in an XP enclosure, but the touchscreen is still open to the environment. How would this differ from mounting in a purged enclosure? This presumes the protruding part of the device is sealed against the atmosphere penetrating through the device into either itself, or the enclosure.

Same goes for NEMA4 rated pb's, or indicators? If they are sealed from the atmosphere, would it be suitable (legal) to mount these in a purged enclosure in a Class 1 Div 1 area?:-?

Remember, that just because you have seen a product, even advertised, it does not mean that it has an approval as an assembly, nor that it even meets the area classification requirements.

Some of the questions you're asking have already been answered directly or indirectly by the quotes from NFPA and other literature.

Remember the BASIC principle: the objective of the 'purged' installations as to separate the ingnitabla atmosphere fromt he source of ignition. So the placement of any equipment inside, outside or on the surface of the purged enclosure - as to be part of the 'wall' of the enclosure - should be bounced against that criteria.

 

[bobgorno]

still not sure if I get it.....so if my purged enclosure is in the C1D1 area, and I put a sealed push button into the door, is that ok? If the sealed push button is illuminated (LED) is that ok? how about an operator touchscreen where the exposed part of the device is sealed from intrusion either into the device or the enclosure....is that acceptable?

An LED or any other pilot light XP assembly would have a pretty sturdy glass lens, a threaded barrel, and an overall construction method that would contain an explosion.

An explosion proof enclosure contains an explosion.

A touch screen is sensitive to touch. It is not likely to find such an animal with an XP rating. How would it contain an explosion if it was sensitvie to touch?

You can purchase an intrinsically safe touch screen for D1 areas.

You can purchase a non-touch screen that is located behind a glass lens in an X-purged enclosure for D1 use. This type would have a membrane style instrinsically safe keyboard for D1 use.

You probably can find an a Zone 1 ATEX approval on a European touchscreen, but that won't help you in the US.

 

[weressl]

An LED or any other pilot light XP assembly would have a pretty sturdy glass lens, a threaded barrel, and an overall construction method that would contain an explosion.

An explosion proof enclosure contains an explosion.

A touch screen is sensitive to touch. It is not likely to find such an animal with an XP rating. How would it contain an explosion if it was sensitvie to touch?

You can purchase an intrinsically safe touch screen for D1 areas.

You can purchase a non-touch screen that is located behind a glass lens in an X-purged enclosure for D1 use. This type would have a membrane style instrinsically safe keyboard for D1 use.

You probably can find an a Zone 1 ATEX approval on a European touchscreen, but that won't help you in the US.

The above does not help much IMHO. It is really immaterial if the device can withstand an explosion since the major part of the devie will be within the purged enclosure where an explosion will not happen, by design. However the parts exposed to the hazardous location need to meet the area T-rating, either by design or by rating.

The issue fo the touchscreen is similar to the above, you are only interested in the surface temperature for one, but you will also be interested if the screen is able to produce any static or other electrical discharge that may be a source of ignition.

 

[bobgorno]

rswolff001's post referred to touchscreens in an XP enclosure. The comment to containing an explosion was in reference to installing a touch screen in an XP enclosure. For the life of me I don't know who would cut a large rectangle out of an XP enclosure and mount a touchscreen in it.

As for a touchscreen in the face of a purged enclosure, without a protective lens in front of it (defeats the purpose of touchscreen), how do you prove the impact resistance of the touchscreen is suitable for a D1 area? Anything protruding through a purged enclosure needs to meet the EAC encountered on the outside of the enclosure.

I'd stay far away from touchscreens in D1 unless they were instrinsically safe. And I would not install an IS touchscreen in an XP box. I there is an explosion in the XP box, the operator will be wearing the touchscreen as a permanent necklace.

BobG

 

[weressl]

rswolff001's post referred to touchscreens in an XP enclosure. The comment to containing an explosion was in reference to installing a touch screen in an XP enclosure. For the life of me I don't know who would cut a large rectangle out of an XP enclosure and mount a touchscreen in it.

As for a touchscreen in the face of a purged enclosure, without a protective lens in front of it (defeats the purpose of touchscreen), how do you prove the impact resistance of the touchscreen is suitable for a D1 area? Anything protruding through a purged enclosure needs to meet the EAC encountered on the outside of the enclosure.

I'd stay far away from touchscreens in D1 unless they were instrinsically safe. And I would not install an IS touchscreen in an XP box. I there is an explosion in the XP box, the operator will be wearing the touchscreen as a permanent necklace.

BobG

still not sure if I get it.....so if my purged enclosure is in the C1D1 area, and I put a sealed push button into the door, is that ok? If the sealed push button is illuminated (LED) is that ok? how about an operator touchscreen where the exposed part of the device is sealed from intrusion either into the device or the enclosure....is that acceptable?

He allready passed the original idea of XP enclosure and it got directed toward the purged enclosure implementation.