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 Post subject: Arc Flash Boundary
PostPosted: Tue May 12, 2015 5:04 pm 

Joined: Mon May 11, 2015 8:13 am
Posts: 1
The work of our service people places them at different customer locations where the majority of the sites do not have equipment 70E labels. Previous editions of NFPA 70E allowed us to use 4 ft as the Arc Flash Protection Boundary which is applicable for systems under 600 V and we incorporated it into our policy. The 2015 edition removed that mention of the 4 ft. I guess we now have to change our policy. But since this edition refers to tables 130.7(15)(A)(b), the flash boundary will be anywhere from 19 inches to 20 Feet.
Does this mean that my company service men have to know the short citcuit available and the OPD clearing time for every piece of equipment they service at the many customer sites the are called?

Does anyone have a suggestion on how to best approach this issue? and kee it simple (why I can't use the 4 feet anymore?)

ps: by mistake I had posted this question at the forum "Question of the Week"

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 Post subject: Re: Arc Flash Boundary
PostPosted: Wed May 13, 2015 5:15 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 879
Location: Rutland, VT
This is a major problem for vendors/contractors who perform work at various customer sites. The customer is considered by OSHA as the Host Employer and is required to inform any contractors of the known hazards that the contractor may be exposed to so that they can protect themselves.

In order to use the tables in NFPA 70E, one needs to know the fault current and clearing time at the equipment being worked on. Additionally, NFPA 70E-2015 states that the owner of the equipment is responsible for arc flash labeling and documentation of that label.

Barry Donovan, P.E.

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 Post subject: Re: Arc Flash Boundary
PostPosted: Mon May 18, 2015 10:00 am 
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Joined: Fri Apr 15, 2011 7:43 am
Posts: 178
Location: Colorado
The arc flash boundary is a simple calculation based on the incident energy. For lack of better terms - it is a reverse calculation to find the distance where 1.2 cal occurs. The 4ft rule probably came close based on the parameters given - maybe, and that is probably why it has been eliminated. Unless the current and the clearing time is known the boundary distance is unknown. In the case of the 4ft rule and the 2 cycle clearing time, it assumes an instantaneous breaker element is tripping the breaker.

I have seen arc flash boundary distances in the hundreds of feet.
The simple answer is there generally no simple answer.

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