On/Off switch inside control panel

[overkill94]

I'm doing a third-party inspection on a fume hood and one of the control panels has what looks like a normal residential on/off switch that doesn't seem to disconnect the power from the whole unit (might just disconnect a certain control circuit). Assuming that's the case, is there any reason a switch like this would not be allowed per UL 508A? I haven't found anything but wondered if anyone knew of anything different.

 

[petersonra]

I'm doing a third-party inspection on a fume hood and one of the control panels has what looks like a normal residential on/off switch that doesn't seem to disconnect the power from the whole unit (might just disconnect a certain control circuit). Assuming that's the case, is there any reason a switch like this would not be allowed per UL 508A? I haven't found anything but wondered if anyone knew of anything different.

why would a fume hood control panel be listed to UL508a in the first place?

if it is being used as a disconnecting means UL508a has a list of what can be used for that purpose.

 

[overkill94]

Well, the unit has a few switches and this small control panel within the unit has both a fuse and a switch so I believe that would require the use of 508A.

I guess the more general question is - can a manual on/off switch be installed within a control panel where the user would be exposed to live parts to flip the switch?

 

[Upnorth]

I guess the more general question is - can a manual on/off switch be installed within a control panel where the user would be exposed to live parts to flip the switch?

As I recall, without looking it up, if the live parts are at a higher potential than "low voltage" parameters allow (e.g. 42.4 or 49 volts, depending upon circumstances), then UL standards for commercial equipment generally require them to be protected from "contact" by a user or operator, during ordinary operation.
When I did UL testing on high-end computer prototypes (in the 80s), we had a "standard finger probe" hmy: that we used for testing whether any live parts could be reached through any openings, when the covers were on and the service access doors were locked (with a key, which is considered a "tool" available only to authorized technicians). If the voltage measured at the fingertip exceeded 42.4 volts, the design failed.

I don't know what the particular standards are for "fume hoods", but my guess (FWIW) is that they are bound by a similar standard of user safety from electrical shock, which I can't quickly access at the moment.

 

[overkill94]

Thanks upnorth.

For this particular installation the only other things in the panel are a fuse in a fully enclosed fuseholder, touch-safe terminal blocks, and a transformer with touch-free terminals. Does that make the inside of the panel "protected from contact"?

It'd be nice if I had more information on what the switch actually controls but I'm pretty sure it's just an isolation switch that wouldn't be used while the equipment was in operation. Then again, what's the point of installing a switch like that?

 

[Aleman]

As far as I know panels are not yet required to have UL508A listing. A switch of that type is an oddball in a panel, but if it's rated for voltage and current then it's probably ok.