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Have you ever reduced the level of PPE from what was calculated in a study?
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 Post subject: Reduced Level of PPE
PostPosted: Sun Feb 05, 2012 12:38 pm 
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Joined: Mon Sep 17, 2007 5:00 pm
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Location: Scottsdale, Arizona
This weeks question is the subject of many debates.

Have you ever reduced the level of PPE from what was calculated in an arc flash study?
  • No
  • Yes - of course comments are always encouraged!

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Jim Phillips, P.E.
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PostPosted: Mon Feb 06, 2012 7:21 am 
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Joined: Mon Jan 18, 2010 11:35 am
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Location: Wisconsin
Study results were done based on 18" working distance, but voltage testing was done with 4ft hotstick.

Decision was made to use 65 cal/cm² colthing even though study results were 43cal/cm² which is usually labeled as 'Dangerous- no acceptable PPE'.

Worst case scenario was when generators were running, dat center made decision that electrical maintenance would not be performed during compromised state (being on generators) so labels were installed showing normal source values.


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PostPosted: Mon Feb 06, 2012 8:48 am 
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Location: Michigan
I've forced breaker panels that meet the 130.3 exception No. 1 (under 240V fed from <125kVA xfmr) to 1.1 cal/cm^2 which is PPE Level 0.


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PostPosted: Mon Feb 20, 2012 9:51 am 

Joined: Mon Feb 20, 2012 9:42 am
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I used Sepam relays to reduce the PPE needed to work on energized equipment.


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PostPosted: Fri Mar 16, 2012 9:31 pm 
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Joined: Thu Oct 18, 2007 7:10 pm
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Location: NW USA
Much work has been spent recalculating system protection settings and configurations to result in lower arc flash calculated values; which often have been reduced from unworkable to HRC 1. Such work represents the larger portion of Arc Flash Studies we have completed.


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PostPosted: Wed Mar 21, 2012 10:48 am 

Joined: Thu Jul 22, 2010 10:24 am
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We reduced the PPE on this arc flash study... hard to make out, but the label indicates HRC 3 inside 120/208 panel. When I reviewed the study data, it took me no time at all to notice they entered breaker clearing times of 2 SECONDS rather than 2 CYCLES into their spreadsheets... Needless to say, I reduced the PPE requirements.


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PostPosted: Wed Mar 21, 2012 11:24 am 
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triptolemus wrote:
We reduced the PPE on this arc flash study... hard to make out, but the label indicates HRC 3 inside 120/208 panel. When I reviewed the study data, it took me no time at all to notice they entered breaker clearing times of 2 SECONDS rather than 2 CYCLES into their spreadsheets... Needless to say, I reduced the PPE requirements.

Are you sure the 2 seconds has not been chosen because of a low arcing current?
IEEE1584 has a 2 seconds rule to limit the incident energy based on the thought that a worker will get out the way after an arc ignites (if he has a place to go).


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PostPosted: Wed Mar 21, 2012 3:31 pm 
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Sort of depends on what you mean by AF study. If it is a full risk assessment then no. But if it's the calculation itself, certainly.

AF calculation only considers consequence, not likelihood of occurrence. Second, sometimes the arc flash hazard boundary produces a nonsensical answer. So if I'm outside of a significant barrier then the arc flash hazard boundary may be meaningless regardless of how many inches the result is. Second, even the 70E Technical Committee has recognized that in some cases the likelihood is remote and thus sets the arc flash PPE requirement to zero. This is after all a risk assessment. Both severity and likelihood enter into the equation for all risk assessment procedures out there.

Also, what about when we have equipment that has not been installed and maintained properly? AF study results then become meaningless, and 70E says this. I've taken the approach here of running the time out to 2 seconds (following IEEE 1584 guidance) in those cases and assuming that the breaker has a much greater risk of failure, high enough that I have to now consider the arc flash hazard if the breaker fails to open on demand.


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