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 Post subject: 1000 second clearing time
PostPosted: Mon Feb 09, 2009 11:49 am 

Joined: Tue Mar 25, 2008 1:00 pm
Posts: 32
Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this?


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PostPosted: Mon Feb 09, 2009 1:14 pm 
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Location: Spartanburg, South Carolina
deprico wrote:
Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this?

Rated current on a 700 kVA (odd size!) transformer is 842A at 480V. The fault current is not reasonable.


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PostPosted: Tue Feb 10, 2009 5:53 pm 
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Location: New England
1600A MCB is a bit oversized. Does it have a rating plug by which you can change the trip value. A trip value of 1200 or even 1000 amps would shift your trip curve. Even without this, your transformer should be 5 to 6% impedance, which means your fault current should be 15,000 amps. With a finite bus around 10 to 12 thousand amps. So you have something wrong.


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PostPosted: Tue Feb 10, 2009 8:37 pm 
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Maybe the software is looking at the incident energy on the line side of the MCB and is reporting the current in a protective device on the primary of the transformer.


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PostPosted: Thu Feb 26, 2009 8:03 pm 
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Joined: Thu Oct 18, 2007 7:10 pm
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deprico wrote:
Is there really any way a 480V panel fed by a 700kva trans is going to sit there and arc for 1000 seconds? It's got a 1600A breaker but the software is telling me its only seeing 350A fault, so its not tripping. How realistic is this?


If the software is saying 350A fault, I assume there is a length of feeder cable that should be protected by a small circuit breaker. I suspect you are missing a circuit breaker from your study (just guessing).

Gary B


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PostPosted: Fri Feb 27, 2009 7:20 am 

Joined: Mon Dec 08, 2008 7:13 am
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Location: Quebec, Canada
jghrist wrote:
Maybe the software is looking at the incident energy on the line side of the MCB and is reporting the current in a protective device on the primary of the transformer.


Deprico: If you're using Easypower, jghrist found your problem. That's just how it presents the results.

See the report «Upstream Trip Device Name».


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