Class 1 Div II Control Panel Requirements;

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andy.sincali@nalasenginee

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Control System Engineer
I have been looking at some of the requirements for a class 1 Div 2 PLC Control Panel and based on some of the information that I have reviewed it appears that if all of the PLC equipment and associated terminal blocks are rated for the area (in my case Groups B,C,D that it does not matter what the actual enclosure is rated. My vendor/ contractor built a pump skid with a Nema4X Class 1 Div 2 SS Enclosure but ran wiring into the panel with no conduits or seals; basically just access holes through the bottom. Is this correct, (does it meet the NEC code)? and do you have any references regarding this issue.
 
My vendor/ contractor built a pump skid with a Nema4X Class 1 Div 2 SS Enclosure but ran wiring into the panel with no conduits or seals; basically just access holes through the bottom. Is this correct, (does it meet the NEC code)? and do you have any references regarding this issue.
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What would trigger the need for seals?

I don't know what you mean by access holes.

It is possibly acceptable as long as there are no hard contacts like relays or contactors inside the panel, unless they are hermetically sealed. This would include any relay contacts used by the PLC.
 
andy.sincali@nalasenginee said:
I have been looking at some of the requirements for a class 1 Div 2 PLC Control Panel and based on some of the information that I have reviewed it appears that if all of the PLC equipment and associated terminal blocks are rated for the area (in my case Groups B,C,D that it does not matter what the actual enclosure is rated. My vendor/ contractor built a pump skid with a Nema4X Class 1 Div 2 SS Enclosure but ran wiring into the panel with no conduits or seals; basically just access holes through the bottom. Is this correct, (does it meet the NEC code)? and do you have any references regarding this issue.
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If the enclosure needs to be 4X any conduit or cable entries would also have to be 4X.
 
There is no such thing as a “NEMA 4X Class 1, Division 2 SS enclosure”. Unless it is also rated NEMA 7, but I’ve never seen an enclosure rated for both.
 
retirede said:
There is no such thing as a “NEMA 4X Class 1, Division 2 SS enclosure”. Unless it is also rated NEMA 7, but I’ve never seen an enclosure rated for both.
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Yep, and some 7 and 9 enclosures do not have any other ratings so they cannot be installed in a wet location.
 
No, I still here but trying to learn the fabrication requirements for a Class 1 Div 2 PLC enclosure; mainly because I think our vendor misrepresented the classification of his design. By the way the PLC control panels and junction boxes are non-purged enclosures with Allen Bradley Compact Logic PLC components which are rated for Class 1 Div 2; but there are no IS Barriers. Also you are correct the terminal blocks are not rated for Class 1 Div2 areas as far as I can see. I think we have a problem but maybe I am wrong, please advise and documentation links would be greatly appreciated. Thanks
 
andy.sincali@nalasenginee said:
No, I still here but trying to learn the fabrication requirements for a Class 1 Div 2 PLC enclosure; mainly because I think our vendor misrepresented the classification of his design. By the way the PLC control panels and junction boxes are non-purged enclosures with Allen Bradley Compact Logic PLC components which are rated for Class 1 Div 2; but there are no IS Barriers. Also you are correct the terminal blocks are not rated for Class 1 Div2 areas as far as I can see. I think we have a problem but maybe I am wrong, please advise and documentation links would be greatly appreciated. Thanks
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For this kind of thing you are looking at non-incendive protection from explosion. You would not need intrinsically safe barriers or purging.

For the most part the only thing you have to worry about are things that might get hot or spark such as a hard contact. Terminal blocks are not an issue.

You might want to read carefully the sections of the code that refers to this protection technique. Unfortunately it's not like it's all in one spot. It is kind of scattered through articles 500 and 501. And you have to read pretty carefully what it actually says rather than what you think it says. It's also somewhat confusing because equipment that is non-incendive is generally not labeled that way. It just says it is okay for class one div two for instance. For some reason the UL product standard does not require it to be labeled as NI.

There is a good chance that you could make a PLC control panel that would be perfectly acceptable for a division 2 area without any special protection means other than NI. I have to admit I am a little nervous about your use of the term access holes to describe how the field wires come into the control enclosure.

If there are motor starters or relays in the box, it probably can't be non-incendive.
 
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