Class 1 Division 1 Ex Cert Process


New member
Houston, TX
I am trying to make sure I understand the process with an NRTL when we go to test/certify our system.

I am working on a product for a C1D1 environment with "Explosion Proof" as the protection method. The system will have a UL listed explosion proof enclosure (modified by the manufacturer for conduit entry) with the appropriate metal conduit and fittings running to a UL listed explosion proof motor. The contents of the enclosure will all be UL Listed for ordinary locations. I'll also have the proper conduit running out of the C1D1 area for power.

Will the NRTL (test lab) require explosion tests as a system? Or because I used an explosion proof motor, enclosure, and conduit, will they not require explosion testing?


Staff member
Mission Viejo, CA
Professional Electrical Engineer
There are several other manufacturer/fabricators here that are better suited to answer this question. While I have certainly required vendors to obtain NRTL certification, I don't tell them or the NRTL how to do it.
Assuming all equipment is installed per its conditions of use, and all of the installation is done correctly, then the NRTL has the option of not doing explosion tests.

The principle is approximately the same as assembling the same equipment in the field. An electrical inspector would verify that it is all installed properly, in which case it is safe. The NRTL can use the same approach, if they feel it is appropriate.

But, if there is any doubt, they can certainly demand explosion tests.

One particular area of concern may be what is placed inside the XP enclosure. Many enclosures have restrictions on what may be mounted, in terms of volume and/or cross-sectional area. In other cases, the lab may not be sure that pressure piling or other effects will not occur, or - in rare cases - there may be some specific piece of equipment in the enclosure that has additional requirements.

Similar considerations will not apply to the motor. That's a buy part.

From this, there is some small chance that the NRTL will want to bang test the XP enclosure, but they (probably) won't want to test the motor or the overall system.