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Old September 13th, 2018, 09:48 AM   #31
g.mccormick
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One question I have is where is the arc flash potential coming from? Is it the drive itself? There are a lot of drives that are available in NEMA4/12/etc. These are typically placed outside of an enclosure on the wall or unistrut. The NEMA ratings does not change the arc flash potential correct? So you would think that a NEMA12 drive on the wall would pose a larger arc flash potential than a NEMA1 drive inside of a panel with a PLC.

Or is the arc flash only considered when "working" on the enclosure?
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Old September 13th, 2018, 10:20 AM   #32
VAN
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Quote:
Originally Posted by g.mccormick View Post
One question I have is where is the arc flash potential coming from? Is it the drive itself? There are a lot of drives that are available in NEMA4/12/etc. These are typically placed outside of an enclosure on the wall or unistrut. The NEMA ratings does not change the arc flash potential correct? So you would think that a NEMA12 drive on the wall would pose a larger arc flash potential than a NEMA1 drive inside of a panel with a PLC.

Or is the arc flash only considered when "working" on the enclosure?
https://www.youtube.com/watch?v=4bBvmPRqfmo

A site I was working at had an old school VFD have an arc flash incident, luckily nobody was around it when it happened (just caught it on camera).
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Old September 13th, 2018, 10:33 AM   #33
Tom Jenkins
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Quote:
Originally Posted by g.mccormick View Post
One question I have is where is the arc flash potential coming from? Is it the drive itself? There are a lot of drives that are available in NEMA4/12/etc. These are typically placed outside of an enclosure on the wall or unistrut. The NEMA ratings does not change the arc flash potential correct? So you would think that a NEMA12 drive on the wall would pose a larger arc flash potential than a NEMA1 drive inside of a panel with a PLC.

Or is the arc flash only considered when "working" on the enclosure?
I'm not an expert, and I don't want to be. The arc flash can occur anytime, but it's effects are most hazardous when the enclosure is open and personnel are in close proximity. I don't know how much a NEMA 1 ventilated enclosure decreases the impact, but I'm sure it helps.

I was standing next to a 300 hp low voltage VFD when it blew. A technician was working on it. No injuries, due to pure good luck, but it sure as he!! scared the bejeezus out of us.
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Old September 13th, 2018, 01:43 PM   #34
g.mccormick
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So I guess the issue is mitigating exposure to the potential arc flash, not the arc flash itself happening.
I'm obviously not very knowledgeable about this though it is something that I should start to learn.

Tom i'm sure that would have scared the hell out of anyone!
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Old September 13th, 2018, 02:11 PM   #35
boardmaker
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One of the most difficult things about arc flash is that it's hard to calculate the potential.


It's not nearly as simple as looking at a chart saying with this voltage and this amperage, then this is your arc flash potential.


I definitely agree with everyone that it's a very important safety issue. I just wish it was easier to calculate and implement.
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