Finger safe equipment and how it affects approach distances and PPE.

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Perean

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I have a question for the very knowledgeable people on this site concerning finger safe equipment in a control enclosure. The enclosure in question is large roughly 3' wide by 3' deep by 7' high. Upon opening the hinged door on the front all the fun fuse blocks, contactors, and transformers are exposed. These cover the interior three walls of the enclosure leaving enough space if you were so inclined to step inside. The box is being fed by a 120 volt 20 amp circuit and has the ability to transform that and output up to 900 VAC for the control of remote elements. All the equipment inside this box is "finger safe". My question is basically this; due to the finger safe designation of the equipment is it permissible for the proverbial "unqualified" worker to enter safely. I am asking because I have been challenged on my assertion that the equipment should be locked out before anyone enter, and preferably before the enclosure is even opened.

I have been digging through my NFPA 70E copy and haven't found as much to support my position as I would like. Since all the equipment could be considered "suitably guarded, isolated, or insulated" I don't know if I can apply any of the rules that would kick in with an exposed electrical conductor or circuit part.

The only thing I am fairly sure I can force is that before any change is made to the system, (i.e. test leads moved from location a to b) I can force a LOTO by using NFPA 70E 130.3. "Only qualified workers shall be permitted to work on electrical conductors or circuit parts that have not been put in an electrically safe work condition". This does not give me all the warm fuzzies though. Even with the equipment being finger safe I would still be very worried about an untrained person being around it.

So if you happen to know of any code or standard references that I can bring to my next meeting with the group working on this enclosure I would appreciate it greatly. I am willing to accept that I may be wrong and that this is a technically acceptable practice but I would much prefer vindication.

The other two areas that I am looking at are the possibility of an increased chance of arc flash NFPA 70E 130.2(2).

Or the possibility that since there are exposed insulated THHN conductors (when the enclosure is open) that this would be considered an Abnormal condition as these conductors are expected to be protected by conduit or some other substantial means.

Any guidance that you can provide would be greatly appreciated.

Thanks
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
This is just an opinion and should not be considered authoritative.

Finger safe equipment is an IEC concept. IMO though, it provides a lot of protection from exposure to energized circuits.

Since 120V supplies do not generally have any appreciable arc flash concerns, you only have to worry about protecting workers from electrocution.

I would be more worried about the 900 Volt side.

Presumably you are training the people who are entering how to do things safely. that makes them qualified.
 
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