Class 1 Division 2 Installation Methods For C1D2 Rated Products


Meridian, ID
Hey all! I did a C1D2 project many years ago and have forgotten some of the painstaking fundamentals I figured out during that project. I've got a PanelView Plus HMI that indicates it is rated for a C1D2 environment. I'm mounting it on a NEMA 4X enclosure. Also mounted on the enclosure are two (2) hermetically sealed pushbuttons. The only thing I have on the backplane of the enclosure are terminal blocks.

My question is, can I just run 24VDC to it from a normal breaker? I know that they will have to seal the conduit when going from the safe area to the hazardous area. I shouldn't have to run the power for the HMI through an intrinsically safe barrier or some other galvanic isolator since all components are rated for C1D2, right?

Allen Bradley indicated that it was ok and they referenced a restricted breathing note:

Restricted Breathing: This is a form of sealing the enclosure with gaskets. The principle employed is that in Division 2 the enclosure is sufficiently tight that it is highly unlikely that a flammable cloud of gas would surround the enclosure for the length of time necessary for enough material to enter the enclosure to produce a flammable mixture.


Staff member
Mission Viejo, CA
Professional Electrical Engineer
"Restricted breathing" for the HMI is not a specifically recognized protection technique in Section 500.7 for Class I, Division 2. It is, however, recognized in Section 505.9(C)(2) for NEC Class I, Zone 2. It is possible that it would be suitable under Section 500.7(L) or 501.5 (Either would take some fairly healthy documentation).

Personally, I would want to see how a NRTL certified (listed or labeled)the HMI. A manufacturer's sales literature wouldn't be enough. (Even their technical literature annoys me sometimes)

The rest of the equipment, as described, should be acceptable.

BTW, Intrinsically Safe or Nonincendive installations can be far more complicated than most electricians and engineers imagine.