HMI on electrical cabinet

[EBell]

I have a 3 phase 480 v electrical cabinet that we will be installing a new PLC in. Currently the plan is to install the HMI on the door of the cabinet. Can someone tell me if this is against code and give me a reference. I have been looking online but have ended up running in circles. My main concern is reducing the arc flash rating of the cabinet itself.

Thanks

Ed

 

[petersonra]

It is a very common practice to mount an HMI thru the door of a control panel. There is no reference to allow this because codes are generally written to either require something very specific or to prohibit it.

There is no such thing as an arc flash "rating".

Often PLC and communications signals are class 2 and thus would need to be separated from the higher voltage stuff.

 

[jim dungar]

Openings in enclosures do not impact arc flash incident energy values.

 

[ron]

Openings in enclosures do not impact arc flash incident energy values.

Generally when the doors are closed and intact based on the listed enclosure, it is safe to walk around the equipment without PPE.
If the door is modified from the listed product, then I would question if the arc flash integrity (whatever small amount there is) with doors closed is impacted. Although most arc flash incidents I would imagine occur with a door open, rodents, reptiles and other contaminants can result in an arc flash with the door closed.

 

[jim dungar]

Generally when the doors are closed and intact based on the listed enclosure, it is safe to walk around the equipment without PPE.
If the door is modified from the listed product, then I would question if the arc flash integrity (whatever small amount there is) with doors closed is impacted. Although most arc flash incidents I would imagine occur with a door open, rodents, reptiles and other contaminants can result in an arc flash with the door closed.

Arc flash incident energy is calculated as if the doors did not even exist.
Door integrity might be considered when evaluating the possibility of an incident occurring (part of the required risk analysis), but it has no bearing on the amount of possible energy (the hazard analysis part).

Adding a listed or recognized HMI would typically not significantly alter an enclosure rating.

 

[Jraef]

If you have GEAR that is specifically listed as "Arc Resistant", then it does matter. "Arc Resistant" is a label that is set up in ANSI C37.20.7 which i technically for medium voltage equipment, but some manufacturers use that same test standard for low voltage gear, because there is no test standard for LV gear as of yet. In order to pass the test for being Arc Resistant, all devices on the door must be tested to be able to withstand the arc blast pressure inside. If not tested, the label cannot be applied.

But that labeling is only available on switchgear and MCCs, not control panels. So that issue of the HMI not being tested (none of them are by the way) is irrelevant.