Class I Div 2 Suitability and Exceptions Around General-Purpose Equipment /General-Purpose Enclosures

[Kedward]

Hello,

I've been working with designs in Class I Division 2 Group B areas for some time, and I've heard a myriad of conflicting information for component selection and requirements. I'm focusing on general-purpose equipment/enclosures.

Let's say I have a random instrument as shown in this link: https://dwyer-inst.com/en/products/pressure/single-pressure/transmitters/series3200g.html

If I needed this device to be explosionproof, I think the installation is pretty straight-forward. However, since it's in a Class I Division 2 Group B area, explosionproof is not required. My past experience with this is that since the device is specifically using the Explosionproof protection technique however, I have to pretty much follow the explosionproof installation outlined in the code. Reviewing some of this and trying to understand General-Purpose Equipment and General-Purpose Enclosures lead me down a different path and I'm hoping I can know if I'm off-base or not.

I start with 501.105(B)(3) and can confirm that the equipment does not have "make-and break or sliding contacts" by removing the mag switches for calibration. Now it's able to be used in a general-purpose enclosure. Then with 500.8(C)(6)(a) the equipment doesn't need to be marked for class, division, group, temperature class, or ambient temperature range.

Now I wire up the components in the provision 501.10(B) with much more freedom because my enclosure is not required to be explosionproof.

My concerns at this point is that I'm not interpreting 500.8(A) appropriately for suitability. I feel like with the mindset that this is a piece of general-purpose equipment that is still approved for it's purpose it can fall under 500.8(A)(1). I also feel like I'm not using a specific protection method listed in 500.7. Maybe it falls under nonincendive equipment, but that doesn't feel like an intentional design decision and I'm unsure if that satisfies the code or not. I compare this to things like RMC/IMC in 501.10(B)(1) or specific motors in 501.125(B)(3) which made me start questioning past rigidity I've experienced in Class I Division 2 areas.

 

[petersonra]

Explosion proof is never required. It is just one protection means.

 

[rbalex]

The general rule for Class I, Division 2 is to avoid equipment that arcs or sparks, or heats above the autoignition in “normal” operation. However normal is not well defined for hazardous locations; e.g., Section 500.8(B)(5) where starting a motor is not considered “normal.”

That said, if you wish to consider Section 500.8(A) for items not specifically listed or labeled see 500.8(A)(3).

 

[Kedward]

The general rule for Class I, Division 2 is to avoid equipment that arcs or sparks, or heats above the autoignition in “normal” operation. However normal is not well defined for hazardous locations; e.g., Section 500.8(B)(5) where starting a motor is not considered “normal.”

That said, if you wish to consider Section 500.8(A) for items not specifically listed or labeled see 500.8(A)(3).

My interpretation of 500.8(A)(1) is a little murky.

I interpret it as I can have a generic 4-20mA transducer with no arc, sparks, or heat above autoignition temperature (I believe 80% auto-ignition temperature is referenced in some spaces) that's listed to UL508 vs a NI transducer listed to UL121201 based on 500.8(B)(3) and 500.8(C)(6)(a) if the generic transducer meets the requirements stated in 501.105(B) as an instrument.

 

[rbalex]

Section 500.8(A)(1) is fairly straightforward. That is, the equipment is listed or labeled (identified) for the intended use. Who applies the mark or label will depend on the applicable AHJ. NOTE: Fed or State OSHA will almost always be “applicable.”

Other markings must comply with Section 110.21. Most (not all) product standard markings will require a temperature indication. Be careful to comply with Section 500.8(C) - all of it. There are some special allowances in Section 500.8(C)(6) including where General Purpose Equipment or enclosures are permitted.

Section 501.105(B) can lay some fairly heavy requirements on GP instruments.