Class I Division 2 NEC Exceptions

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gerbonic

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This question is about NEC Article 501.105(B).
The article provides guidance for instruments in Class I Division 2 area.

I have had many discussions with people of varying levels of experince and there seems to be widespread opinion regarding what kind of instrumentation is acceptable in a CID2 area and what kind of enclosures or additional protection is required.

The widespread opinion seam to stem from the Exceptions in 501.105(B)(1) versus the Exceptions in 501.105(B)(2)

(B)(1) clearly spells out a requirement for non-incendive, hermetically seals, oil immersed or listed devices. However (B)(1) applies only to Contacts

(B)(2) applies to Resistors and Similary Equipment and the exception for (B)(2) says that GP is permitted if it meets the T rating requirment and it has no contacts.


How do we apply this to general purpose instrumentation (generally 24VDC) such as flowmeters, DP meters, etc? How do people generally determine if any certain piece of instrumentation falls under the (B)(2) exceptions or not? Is this left up to the AHJ or is there a hard rule to go by. I have always applied the (B)(1) requirements to instrumentation, but with so many different opinions, I figured I would go get a few more :lol: .
 
I seem to recall Bob Alexander pointing out once that there are resistors in just about every piece of electronic equipment, thus triggering the requirement it be listed for the area classification.

These days there are plenty of choices for instruments and other devices that are listed for classified areas. Why try to make up your own rules about what is usable? Just let UL or FM or someone else who is far more qualified to do so make that choice for you.
 
The exception in501.105(B)(2) specifically apply to resistors.

The goal is not to re-invent the wheel here. In an ideal green field, all the instrumentation would be specd out as required. However, areas change classification and a place which was previously GP might become CI D2 in the future. In those scenarios it would be best to be able to utilize all options available.

If the exceptions were not intended to be used, then they should be removed and say all components in a class I div 2 area should be listed for the area. If we take it to the extreme then eveything down to a standard terminal block should be listed CID2. I think there is a middle ground somewhere.
 
I would not consider a process transmitter to fall under either exception (although some might have contacts for alarming and will likely have integral resistors and other electronic components). I would always assume 500.8 would apply and the instrument needs to be listed for Cl I Div2, unless it is a simple apparatus and an IS protection technique is used. I wouldn't consider a transmitter to be a 'resistor or similar equipment'.
 
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