Control Boxes in Hazardous Areas
- Thread starter mull982
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petersonra
Senior Member
- Location
- Northern illinois
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- engineer
rcwilson
Senior Member
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- Redmond, WA
120V "Controls" in Classified Area
120V "Controls" in Classified Area
There's not enough information to give a good answer. What ever you install, it must be listed for the area classification and comply with Article 500 & 502.
If ?controls" just mean a pushbutton station, install a NEMA 7 station with listed pushbuttons and the appropriate conduit seals at the correct locations. Or use a NEMA 4 box with factory-sealed pushbuttons listed for the area classification. If controls includes relays, or circuit boards, or motor starters or power supplies or ???, they have to be in a listed enclosure with proper seals.
A device?s suitability for use in a classified area does not depend on the operating voltage. We can't just say that it?s not hazardous because it?s low voltage.
Look at the web sites for Appleton and Crouse-Hinds or other manufacturers. They have some excellent tutorials on hazardous area installations.
120V "Controls" in Classified Area
There's not enough information to give a good answer. What ever you install, it must be listed for the area classification and comply with Article 500 & 502.
If ?controls" just mean a pushbutton station, install a NEMA 7 station with listed pushbuttons and the appropriate conduit seals at the correct locations. Or use a NEMA 4 box with factory-sealed pushbuttons listed for the area classification. If controls includes relays, or circuit boards, or motor starters or power supplies or ???, they have to be in a listed enclosure with proper seals.
A device?s suitability for use in a classified area does not depend on the operating voltage. We can't just say that it?s not hazardous because it?s low voltage.
Look at the web sites for Appleton and Crouse-Hinds or other manufacturers. They have some excellent tutorials on hazardous area installations.
Basically what I am referring to is a controller, and touchscreen panel which houses a circuit board with various 120V inputs and outputs. I'm trying to figure out what kind of enclosure I need to house this in.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Many PLCs and associated I/O are listed for class 1, division 2 areas (although relay output modules aren't).
weressl
Esteemed Member
Walking all over the map with terminologies.
Class II locations are those that are hazardous because of the presence of combustible dust.
Depending on the severity of the expected dusting the equipment utilized in these areas are looked at for the following:
Depending on the severity of the expected dusting the equipment utilized in these areas are looked at for the following:
- Do they have hot external surfaces,
- Do they prevent ingress of dust into the enclosure,
- Do they present a dust buildup surface by gravity where the trapped heat would/could become a source of ignition.
Class I locations are those in which flammable gases, flammable liquid?produced vapors, or combustible liquid?produced vapors are or may be present in the air in quantities sufficient to produce explosive or ignitible mixtures.
Whole different kettle of fish, different problems addressed differently.
Divisions 1 and 2 express the likeliness or frequency that the above conditions under either Cl. I or Cl. II may exist.
If you don't know what area you have, which is what I can gather form your description, you have no business deciding what equipment is suitable for either location.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
That sounds a bit odd.
weressl
Esteemed Member
Why do you think so?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Its odd because I don't think I have ever seen anyone do that before.
I am not suggesting it is a violation of some code, just unusual.
There is no reason a NEMA3R box cannot be used for that purpose, but they may not be well suited for it, especially in some styles.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
From this site:
http://www.nema.org/prod/be/enclosu...=500&rdepth=0&sufs=0&order=r&cq=&id=4b4da2c87
Also, 502.10(B)(4).
Do you really have to install this in a Class 2 area? Is the area properly classified?
Last edited:
weressl
Esteemed Member
Agreed, it is usually NEMA 4. Proper gasketing could take care of the issues with NEMA 3 also, but it is a modifiction.
weressl
Esteemed Member
Hmmmm...not exactly sure what you are trying to say or ask here.
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
I'm out of town right now and don't have my code book, but I believe that section was saying the box needed to be rated for the location.
The question was 2 part, 1-can the box go elsewhere? Does it really have to go in the Class 2 location? 2-Is the area truly a class 2 location? I've seen people claim areas were class 1 locations when in reality they were close to it and not really a class 1 area and I was just wonder if this might be similar.
weressl
Esteemed Member
Any purged (NFPA496) NEMA box would be considered rated for the location.
It sounds like that the equipment is an operator MMI that implies that it needs to be in close proximity of the operation are.
Certainly the proper area classification is paramount in deciding what type equipment is needed and locating equipment always in the 'lesser' classifications is a ground rule of good engineering practice.
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