UL508A - Distance ventilation openings

U

Uze

Member
Location
France
Occupation
Engineer
Hi everyone,

I would like to use ventilation for my electrical cabinet. When I read UL508A point 22.1 "Ventilation Openings," I see that I need to have at least 305 mm between the opening and a "possible source of arcing."


My First question: The ventilation manufacturer told me that the filter is UL94 5VA. Does this mean I don’t need an additional barrier? Is that correct? In UL 508A, I don’t see anything about this.


Second question: What should I consider a "possible source of arcing"? Does this include all of my power circuits?

Thank you in advance for your reply
"22.1 Unless a ventilation opening is located at least 12 inches (305 mm) from an arcing part, a barrier of metal or of a material such as those specified in 22.4 shall be interposed between the ventilation opening and a possible source of arcing, such as a power-circuit disconnect switch, the vent openings of a circuit breaker, a contactor, or an overload relay."
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Uze said:
Does this include all of my power circuits?
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It includes those power devices which open/break/interrupt current using contacts exposed to air. Think of all air break switches.
It would not include sealed or non-air break devices like solid state components or those sealed like fuses.
 
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Thank you for your responses.
Have you already received feedback the ventilation filters can be considered as a barrier?
 
Uze said:
The ventilation manufacturer told me that the filter is UL94 5VA
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UL94V is basically just a UL standard for plastics used in electrical applications, pertaining to it's ability to spread flames vertically, and the 5VA just means it will self extinguish at least 5 times. Any piece of plastic used in electrical equipment must be UL94V listed. It has no relation to anything else.

That said, Section 22 does not state the PURPOSE of the barriers, but the PRECEDING section, 21, and in particular 21.2.2 says;
A ventilation opening that serves as an air outlet of exhaust air from a forced ventilation system shall not direct air at the area occupied by the equipment operator.
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That to me, along with the mention of "arcing parts" in 22, implies that the concern is not flammability of the vent parts, it is in protecting people from the effects of arcing components possibly causing an arc flash event. Again, that is not STATED, but my point is that the fact that the vent parts have a UL94V listing is not something I would consider relevant to the likely issue in consideration.

As an aside, I have built many many ICPs where there is an MCCB used as the main disconnect near the top of the enclosure, I have never once had a UL inspector check that distance to a vent opening in the top. I have on the other hand had them make me install a baffle for the vent grille because of a contactor too near the top or bottom opening.
 
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