I have an inquiry on Nonincendive control circuitry in Class I div 2
environments. What is the procedure on using nonincendive circuits?
Does mearly buying nonincendive rated equipment qualify? I am
requesting information, hints, web sites from those of you who may be
more experienced in this area. This seems to be a fuzzy area of
control wiring. Thanks to all.

Robert Most

 

NO, mearly buying rated equipment does not qualify.
Generally speaking, there are one of two of two choices.
1. Rated devices with sealed rigid conduit. This is all about isolating sources of electrical energy from explosive materials, and preventing the migration of explosive material back to the control panel. Rated devices are usually bulky, have seals, and require installation by a certified electrician CAPABLE AND EXPERIENCED in such environments. Rigid conduit, not electrical metal tube (EMT),provides the mechanical protection. Seals for this conduit must be outside the rated zones. If the seals are not done correctly, you have a dangerous situation.
2. Non-Rated devices with zener barriers. This is all about limiting the current through electrical devices to below the ignition threshold. This is suitable only for dry contacts or NAMUR two-wire devices that behave like a dry contact. This is absolutely NOT SUITABLE for solenoids or three-wire devices such as proximity switches with separate power wires. Although, this does not address the migration of explosive material.

And finally, IF YOU HAVE ANY DOUBTS, HIRE A CONSULTANT TO DO THE WORK TO LIMIT YOUR OWN LIABLITY. In fact, HIRE A CONSULTANT ANYWAY, REGARDLESS OF WHETHER YOU THINK YOU KNOW WHAT YOU’RE DOING.
You have the lives of others in your hands.
Anthony Kerstens P.Eng.

 

Robert,
You will find a great deal of useful information in the National Electrical Code, 1999 issue.

http://www.nfpa.org

If you are unable to obtain information, please post your specific question.

Phil Corso, PE
Trip-A-Larm Corp

 

Nonincendive circuits and field wiring is defined in the US National
Electrical Code(NEC) in Article 100 and its use in Article 500 and 505. ISA
Standard S12.12 "Nonincendive Electrical Equipment for Use in Class I and
II, Division 2 and Class III, Division 1 and 2 Hazardous(Classified)
Locations" further defines nonincendive systems. An IEC standard for this
type of protection(called Type Ex "n") is IEC 79-15 "Electrical Apparatus
with Type of Protection "n" ". Another reference is "Electrical Instruments
in Hazardous Locations, 4th. Ed", by Ernest Magison, published by ISA(ISBN
1-55617-638-4).


William(Bill) L. Mostia, Jr. PE
Principal Engineer
WLM Engineering Co
Independent I&E Consultant
P.O. Box 1129
Kemah, TX 77565
E-Mail: [email protected]

These opinions are my own and are offered on the basis of Caveat Emptor.

The difference between genius and stupidity is that genius has its limits
Experience without understanding is ignorance.