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 Post subject: 4 Foot Flash Protection Boundary??Posted: Wed Jul 04, 2007 8:02 am

Joined: Wed Jul 04, 2007 7:58 am
Posts: 3
We are in the middle of conducting our first arc flash study. We are getting many calculated flash boundaries of less than the 4 foot distance that NFPA 70E has. Do any of you use the smaller calculated boundaries or do you use the 4 foot distance as the minimum??
b.t.w. Nice Forum!

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 Post subject: Posted: Wed Jul 04, 2007 3:27 pm

Joined: Tue Jul 03, 2007 5:00 pm
Posts: 45
Location: Michigan
4 Foot Boundary

We started out using the calculated numbers, but then decided it would be more consistant to adopt a standard "minimum" distance of 4 feet. We have a few distances greater than 4 feet but 4 is our minimum.

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 Post subject: Posted: Wed Jul 04, 2007 3:33 pm

Joined: Wed Jul 04, 2007 7:58 am
Posts: 3
4 Foot Boundary

Joe B - what do you post on the labels? 4 ft?

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 Post subject: Posted: Wed Jul 04, 2007 4:44 pm

Joined: Tue Jul 03, 2007 5:00 pm
Posts: 45
Location: Michigan
4 Foot Boundary

We use the labels generated by the program so the distance will vary. We use 4 ft. as part of our electrical safety standard.

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 Post subject: Posted: Tue Nov 20, 2007 10:50 am

Joined: Tue Nov 20, 2007 10:41 am
Posts: 4
Default Arc-Flash Boundary

The default arc-flash boundary for systems 600V and less is 4 feet. However, it depends on the available fault current and clearing time of the overcurrent protective device. According to NFPA 70E, the combination cannot exceed 300,000 Amp-cycles. What this means - is that if the available fault current is 50,000 amps, then the clearing time cannot exceed 6 cycles (100 milliseconds).
Ken Cybart
Littelfuse, Inc.

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