HMI in Class 1 Div 2 area


Thread Starter


I have a HMI Located in a class 1 div 2 enclosure. The enclosure is heated with a class 1 div 2 heater as the building heat is turned off from time to time.

Since everything is rated class 1 div 2 I didn't think much of it. When the panel was installed I noticed the connection to the heater was a "sealed" connection which is required for class 1 div 2.
However the wiring within the panel to the HMI is not using Class 1 Div 2 method. Thus when the panel door is opened, the panel is no longer rated class 1 div 2.

The HMI is powered by 24VDC (7 watts) and is class 1 div 2 rated. Could I simply use an intrinsically safe barrier or isolator for the 24 VDC power feeding the HMI? If not then I think the only options are for the operator to have a gas monitor when operating the HMI or we move the HMI panel to a non-classified area.

Any advice would be appreciated.


Bob Peterson

Given that you stated this was a C1D1 area, the use of a gas monitor is very dubious as a way of creating a "safe condition". It is probably unnecessary as well. There should be a control drawing that came with the C1D2 rated stiff that shows how it is supposed to be wired.

in any case, the operator should never be opening the door to the cabinet in the first place. If there is some reason he has to do that, there is a major design flaw that needs to be corrected.