Help with Class 2 Div 1 and Class 2 Div 2

[amgar]

Background - I am more of a PLC programmer than an electrician. We are quoting a few pieces of equipment, some of which will be going into a hazardous location. It has become my responsibility to try to put together a cost estimate for the required electrical hardware, junctions boxes, etc. The engineering company has stated that the control panel and PLC will be installed in an unclassified location but that devices/instrumentation installed inside the equipment will need to be suitable for class 2, div 1, group G. Devices installed on the exterior of the equipment will need to be class 2, div 2, group G. I have done a bit of reading in NFPA70, article 502, but I still have a few questions.

1. Does the PLC and associated I/O modules (installed in the unclassified location) need to be rated for the appropriate hazardous location if interfaced with devices inside the hazardous area?

2. According to article 502-6(b), class 2 div 2 locations require only that the enclosures be dust-tight. Can components (such as a remote PLC I/O rack) not specifically marked for class 2 div 2 be installed within this dust-tight enclosure?

3. It appears that dust-ignitionproof enclosures are only required in regards to class 2, div 1 locations. Article 502-5 requires appropriate sealing between dust-ignitionproof enclosures and non-dust-ignitionproof enclosures. Are there any similar requirements for sealing dust-tight enclosures from enclosures in an unclassified area?

4. What is the role of intrinsic safety? After reading 500-2(a)(4) it appears to allow for normal installations by removing the requirements of article 502.

Thanks!

 

[amgar]

My original post referenced parts of the NEC from my outdated copy at home. I have modified the quote below to reference 2011 code sections.

Background - I am more of a PLC programmer than an electrician. We are quoting a few pieces of equipment, some of which will be going into a hazardous location. It has become my responsibility to try to put together a cost estimate for the required electrical hardware, junctions boxes, etc. The engineering company has stated that the control panel and PLC will be installed in an unclassified location but that devices/instrumentation installed inside the equipment will need to be suitable for class 2, div 1, group G. Devices installed on the exterior of the equipment will need to be class 2, div 2, group G. I have done a bit of reading in NFPA70, article 502, but I still have a few questions.

1. Does the PLC and associated I/O modules (installed in the unclassified location) need to be rated for the appropriate hazardous location if interfaced with devices inside the hazardous area?

2. According to article 502.115(B), class 2 div 2 locations require only that the enclosures be dust-tight. Can components (such as a remote PLC I/O rack) not specifically marked for class 2 div 2 be installed within this dust-tight enclosure?

3. It appears that dust-ignitionproof enclosures are only required in regards to class 2, div 1 locations. Article 502.15 requires appropriate sealing between dust-ignitionproof enclosures and non-dust-ignitionproof enclosures. Are there any similar requirements for sealing dust-tight enclosures from enclosures in an unclassified area?

4. deleted

Thanks!

Sorry about that.

 

[rbalex]

1. No. In this case, only the wiring methods actually inside the classified location must be identified for Class II.

2. Yes.

3. No. The distinction is for enclosures "... required to be dust-ignitionproof and one that is not..." That said it, it is often prudent to to use 502.15 (2), (3) or (4) as if the dusttight enclosure were dust-ignitionproof, but not absolutely necessary.

4. I note you deleted it, but for future reference Article 504 still has some rather intricate requirements for separation, grounding, bonding and sealing.

General Note. See NFPA 499 for a better understanding of classification practices. You are fortunate that this is a Group G application. Good housekeeping practices can often reduce or eliminate a great deal of the need to classifiy.

 

[amgar]

rbalex,

Thanks for the comments. It seems I am on the right track as your answers to 1 & 2 confirmed what I believed to be true.

It appears that I can use my normal PLC components (I was considering the $$$ Flex EX, http://ab.rockwellautomation.com/io/1797-flex-ex-io) and install them within the appropriate dust-tight or dust-ignitionproof enclosures. Of course all wiring to field devices will have to be in accordance with 502.10.