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 Post subject: Old arc flash study
PostPosted: Tue Jul 06, 2021 8:47 am 

Joined: Wed Aug 06, 2014 7:17 am
Posts: 1
A customer has been using a number of circuit breakers with different interrupt ratings. When questioned he referred to an arc flash study dated 2011. This study listed a hazard risk level at each level of the single-line, only stating the arc flash boundary, the available energy, and the required PPE level.

Can I translate this to a SCCR level at each panel? I think not and a co-ordination study is necessary. Any Forum advice is appreciated.


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 Post subject: Re: Old arc flash study
PostPosted: Wed Jul 07, 2021 2:22 pm 
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Joined: Thu Apr 18, 2019 11:42 am
Posts: 56
Sounds like maybe the table method was used, using maximum fault current? I would agree...a new study (AF/TCC/SC) would be worthwhile and if you can get the actual available fault current from the utility...even better.

Mike


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 Post subject: Re: Old arc flash study
PostPosted: Sun Jul 11, 2021 10:08 am 
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Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1605
Location: Scottsdale, Arizona
SRWflash wrote:
A customer has been using a number of circuit breakers with different interrupt ratings. When questioned he referred to an arc flash study dated 2011. This study listed a hazard risk level at each level of the single-line, only stating the arc flash boundary, the available energy, and the required PPE level.

Can I translate this to a SCCR level at each panel? I think not and a co-ordination study is necessary. Any Forum advice is appreciated.


The short answer is No.
The SCCR is the short circuit current that the device is rated for. The actual short circuit current that could flow during a fault will vary depending on many factors such as conductor and transformer impedance, configuration, utility strength etc. The current that flows during an arc flash (arcing current) would be even less.

Expanding on MSParent's comment, did the previous study use the SCCR as the short circuit current for the study? That could lead to possible problems such as indicating a protective device operates quickly for the higher fault current and if the actual current is lower, the device could take longer.

You mentioned calculated incident energy so it sounds like calculations were performed. Someone needs to evaluate the previous study in more detail to determine what assumptions were made and if they are correct / conservative.;

An easy answer is the study is from 2011. NFPA 70E states that studies should be reviewed at intervals not to exceed 5 years (or if major changes occurred) so bottom line, it is time to take a look at the 2011 study.


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