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 Post subject: Bit of plea
PostPosted: Thu Aug 27, 2009 11:39 pm 
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Joined: Thu Aug 27, 2009 11:28 pm
Posts: 2
Alright, So here is the scenario. Two weeks ago I was hired at a manufacturing facility as an Electrical Engineering intern. About a week after, I was assigned the task of updating an Arc Flash study done by an outside contractor.

Here's what has fallen in my current realm of understanding:

1. IEEE Incident energy calc
2. Arc Current Calc
3. Safe working distance and PPE level assignments.

However, I'm mildly frustrated with my inability to wrap my head around calculating "Bolted Fault Current". Most of the new equipment ranges from 240 VAC to 480 VAC panels. Some have been kind enough to provide a maximum short circuit current etc etc, making my life much easier. However, some inconveniently leave these values out, are in a foreign language, or are down right stubborn. Everything is fed from an overhead Bus that already has had Arc flash studies performed upon it.

So long story short, I need to get from point A to B, find the bolted fault current for these various panels, so I can move on with the Arc Flash calculations.

Unfortunately a software solution is not an option, I"m strictly looking for a hand analysis of the process.


Thank you all in advance!


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PostPosted: Fri Aug 28, 2009 12:10 am 
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Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
DougL wrote:
Alright, So here is the scenario. Two weeks ago I was hired at a manufacturing facility as an Electrical Engineering intern. About a week after, I was assigned the task of updating an Arc Flash study done by an outside contractor.

Here's what has fallen in my current realm of understanding:

1. IEEE Incident energy calc
2. Arc Current Calc
3. Safe working distance and PPE level assignments.

However, I'm mildly frustrated with my inability to wrap my head around calculating "Bolted Fault Current". Most of the new equipment ranges from 240 VAC to 480 VAC panels. Some have been kind enough to provide a maximum short circuit current etc etc, making my life much easier. However, some inconveniently leave these values out, are in a foreign language, or are down right stubborn. Everything is fed from an overhead Bus that already has had Arc flash studies performed upon it.

So long story short, I need to get from point A to B, find the bolted fault current for these various panels, so I can move on with the Arc Flash calculations.

Unfortunately a software solution is not an option, I"m strictly looking for a hand analysis of the process.


Thank you all in advance!



Wow, trail by fire huh? No software? Have fun. This should help.
http://www.cooperbussmannstore.com/pc-46-9-electrical-plan-review-epr.aspx


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PostPosted: Fri Aug 28, 2009 4:43 am 
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Joined: Thu Jul 19, 2007 7:54 am
Posts: 201
Location: St. Louis, MO
First tip - read the contractors study!
Pay special attention to their assumptions and disclaimers. Check these against actual conditions where you can. They may not have had as good access to the equipment as you do.

Second tip - Don't confuse equipment interrupting ratings with available fault current. You will need to calculate the available fault current yourself. There are many programs online that can do this, and few downloadable excel sheets. I would also advise getting one of the manuals on short circuit calculations available from GE or CooperBussman. (If you know a local salesman, they may be able to get you a copy for free, if you can't download it.)If the previous study provides the available fault current of the overhead bus that the equipment you are interrested in is fed from, start there. (Provided their assumptions, etc are correct.)

That should get you started. Welcome to the forum and come on back when you are ready for more!


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PostPosted: Mon Sep 14, 2009 10:59 am 
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Joined: Wed Jun 10, 2009 5:00 pm
Posts: 204
Location: Toronto
check A Handbook to Accompany the Online Short-Circuit Calculation Program describing MVA method for short circuit analysis and its online implementation.

_________________
Michael Furtak, C.E.T.
http://arcadvisor.com


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PostPosted: Thu Sep 17, 2009 1:26 am 
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Joined: Thu Aug 27, 2009 11:28 pm
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First off, I I'd like to thank everyone for the replies. The project was put on the back burner for a week or so, but its grabbed the big boss's attention again. I've a bit of studying up to do, but I'll be back to post any other road blocks. Again, thank you all for your help


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