Hazardous Area Classification

What is meant by Hazardous area classification for PLCs ? What is Class and Div ? Do any Safety PLCs comply with these Class and Div ? What about Rockwell GuardPLcs ? Anybody have any idea on this ?

Please help !!

A very in depth subject

The NEC Code will offer information on this as will:
http://www.osha.gov/pls/oshaweb/owasrch.search_form?p_doc_type=STANDARDS&p_toc_level=0&p_keyvalue=

Another very informative site is:http://www.sti.com/safety/index.htm

Hazardous classification in the US is defined by NEC Article 500.5 states the Classifications.
Class I: Locations which flammable gasses or vapors are or may be present
Class II: Hazardous because of the presence of combustible dust.
Class III: Presence of easily ignitible fibers or flyings, but in which the fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitible mixtures.

Each Class has a Division I or II that offers more specifics to the degree of hazard.

I am not sure where the Safety PLC's like AB GuardPLC (formerly PILZ I believe) fall in the NEC hazardous classification, I would have to download the manuals and tech sheets. They have a tendency to follow IEC guidelines which arent always as harsh as NEC or ANSI.

I would expect the plc to be in the "safe " area, and interface with the sensors etc via zener barriers and galvanic isolation barriers, or be inside a suitably rated ( probably flameproof) enclosure.
There is a new standard " ATEX" which is coming into force this year in the european community,which incorporates dust hazards as well as gas.

As fas as I know, the safety PLCs are "safe" only in regards to operational safety (two-hand starts and the like), not hazardous safety.

Another buzzword you'll see used in hazardous (Class 1, Div 1 or 2) areas is "intrinsically safe". Basically, it means that there is zero chance that it will cause a spark.

To put a PLC in a hazardous environment, you need to put it in a special enclosure which can be pressurized (so that no explosive gases/dust/fibers can come in and be detonated by the "sparking" PLC).

I've seen some plc equipment w/ Class I Div. 2 hazardous location ratings. The Schneider Momentum PLC has a cert. for Class I Div. 2 from FM.

http://www.modicon.com/85256AE8006D7893/all/852566B70073220C85256990005BB8B1!OpenDocument&prod=noopen

Unfortunately I haven't seen any mention that this PLC has any type of SIL (safety integrity level) rating that would equal the safety ratings of the AB. I've seen that some of Triconex products have safety ratings + the haz. loc. ratings, but they might be overkill for your app. (and big $$$ too!).

http://www.triconex.com/products/trident/certs.asp

To place any of this equipment in a classified location requires special precautions to ensure safe operation. These ratings may save you a few $$ in special enclosures (purging etc...) but there might be an offset in the installation. Research as much as you can about the proper installation before jumping into the project. (NEC art 500 thru 505 would be an excellent start).

http://www.nfpa.org/catalog/

Bob

Every one of my installations are in a Class I, Div 2 hazardous area.
I use the A-B ControlLogix system which is suitable for mounting in Class I, Div 2. The PanelView is suitable for the hazardous location as well.

I think that Siemens and possibly others have PLCs rated for Class I, Div 2.

Class 1, Div 1 is another story. You will need to use an explosion proofing method such as purging and pressurization or Ex-d enclosures (explosion-proof :angr: )

by the way...

Definition of Hazardous locations...

Check out these links, they have decent summaries of haz location definitions..

http://www.cullen-exi.com/index.htm
click on the Haz Facts button

UL's link
http://www.ul.com/hazloc/index.htm

Bob