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 Post subject: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 9:18 am 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
I have a small site built in SKM. I have a main breaker in a piece of switchgear then that feeds an I-Line panel. The main breaker has 10.39 cal/cm^2 and 93 inch flash boundary. 15 feet away the I-Line has 15.37 cal/cm^2 and 89 inch boundary. Does this make sense to anyone else. SKM said it was due to the Switchgear and panel designations. Higher incident value would always have a larger boundary right? Still does not ring right with me. Any feedback? Thanks


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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 10:38 am 

Joined: Tue May 29, 2018 8:19 am
Posts: 44
There are several possible considerations. What SKM told you is a possibility, depending on the type of equipment you have selected, enclosure size, bus configurations. It's not clear if your IE values are at the panel buses or load sides of the breakers. If your panel has a main breaker and you don't have "check upstream mis-coordination" checkbox checked, it may be basing the calculation on the time-current characteristics of the panel main alone. A system 1-line would be very helpful in providing more meaningful responses.

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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 11:04 am 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
I think I got it put up there.


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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 11:36 am 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
I also do have the check upstream device checked.


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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 12:04 pm 

Joined: Tue May 29, 2018 8:19 am
Posts: 44
Did you try running it with the motor turned off?
There is something strange happening between Xfm#1 Sec (20.5 Cal) and #1 Xfm MDP Main Brk Encl (10.4 Cal).

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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 1:34 pm 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
The motor does not seem to make a difference. I assumed the transformer secondary is due to the cable. I have seen that before. The the other issue is throwing me for a loop. Just does not feel right.


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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 15, 2023 1:36 pm 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
I have also removed the enclosure dimensions and that did change the numbers but they were still wrong with the shorter boundary with the higher energy.


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 Post subject: Re: Arc Fault calculations.
PostPosted: Mon Sep 18, 2023 7:09 am 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
So I removed the busses I am questioning and put in another bus with no data attached. The numbers seem right on that one. So I guess I am down to trying to figure out why a switchboard and a panel would have formulas to make the flash boundary go down when the incident energy goes up? That is what SKM said the software was doing but still does not make sense. Any thoughts?


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 Post subject: Re: Arc Fault calculations.
PostPosted: Mon Sep 18, 2023 11:10 am 

Joined: Tue Jun 14, 2022 11:35 am
Posts: 15
rshummel wrote:
So I removed the busses I am questioning and put in another bus with no data attached. The numbers seem right on that one. So I guess I am down to trying to figure out why a switchboard and a panel would have formulas to make the flash boundary go down when the incident energy goes up? That is what SKM said the software was doing but still does not make sense. Any thoughts?


Your datablock does not show the working distance, but unless you changed them, SWGR is 24" and PNL is 18" so that may account for the difference in IE.


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 Post subject: Re: Arc Fault calculations.
PostPosted: Mon Sep 18, 2023 11:13 am 

Joined: Mon Aug 17, 2020 8:38 am
Posts: 15
That makes sense. Thanks, this one was confusing me.


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 Post subject: Re: Arc Fault calculations.
PostPosted: Fri Sep 22, 2023 10:26 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 571
Location: Wisconsin
Win Engineer wrote:
rshummel wrote:
So I removed the busses I am questioning and put in another bus with no data attached. The numbers seem right on that one. So I guess I am down to trying to figure out why a switchboard and a panel would have formulas to make the flash boundary go down when the incident energy goes up? That is what SKM said the software was doing but still does not make sense. Any thoughts?


Your datablock does not show the working distance, but unless you changed them, SWGR is 24" and PNL is 18" so that may account for the difference in IE.


And switchboards are typically treated as panels, for arc flash, due to their similar breaker and bussing connector. Switchgear usually involves drawout breakers with cable compartments in the rear of the equipment. Check the UL listing.


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