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 Post subject: Incident Energy andCL Fuse Equations
PostPosted: Mon Feb 01, 2010 12:20 pm 

Joined: Thu Apr 30, 2009 11:08 am
Posts: 4
Does anyone else have a problem with the IEEE 1584 incident energy equations for current limiting fuses?

Incident energy is based on the arcing fault current, not the bolted fault current. Arcing fault current is determined from the bolted fault calculation but takes several other variables into consideration, like system voltage, gap, etc. The CL fuse incident energy equations only use bolted fault values.

Why are the CL fuse equations based on bolted fault rather than arcing fault values?

For now, I am not using the equations in my analysis. Are my concerns unfounded?

Thanks.


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PostPosted: Mon Feb 01, 2010 1:02 pm 
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Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
SJB wrote:
Does anyone else have a problem with the IEEE 1584 incident energy equations for current limiting fuses?

Incident energy is based on the arcing fault current, not the bolted fault current. Arcing fault current is determined from the bolted fault calculation but takes several other variables into consideration, like system voltage, gap, etc. The CL fuse incident energy equations only use bolted fault values.

Why are the CL fuse equations based on bolted fault rather than arcing fault values?

For now, I am not using the equations in my analysis. Are my concerns unfounded?

Thanks.



Current limiting fuses are only effective at reducing Ei when operating in the current limiting range, something the fuse manufacturers don't like to talk about.


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PostPosted: Mon Feb 01, 2010 7:46 pm 
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Joined: Sun Dec 23, 2007 1:44 pm
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Location: Charlotte, NC
But the protection guys must know!


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PostPosted: Tue Feb 02, 2010 7:26 am 
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Joined: Mon Jun 02, 2008 11:58 am
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acobb wrote:
But the protection guys must know!


Know how to best sell fuses that is.


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PostPosted: Tue Feb 02, 2010 8:55 am 
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Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1503
Location: Scottsdale, Arizona
SJB wrote:
Does anyone else have a problem with the IEEE 1584 incident energy equations for current limiting fuses?

Incident energy is based on the arcing fault current, not the bolted fault current. Arcing fault current is determined from the bolted fault calculation but takes several other variables into consideration, like system voltage, gap, etc. The CL fuse incident energy equations only use bolted fault values.

Why are the CL fuse equations based on bolted fault rather than arcing fault values?

For now, I am not using the equations in my analysis. Are my concerns unfounded?

Thanks.


During the development of IEEE 1584, had only a handful of tests with current limiting fuses. CL fuses have a different response depending on how much short circuit current is flowing and whether the current is in the CL range or the non CL range.

It is easier just to measure the incident energy and create an equation rather than try to predict the arcing current which is based on the fuse operating in its current limiting mode.

You can still have a high incident energy while using CL fuses if they respond too slow. If the short circuit current is too low, the fuse can take time to respond similar to breakers and other devices. The CL fuse must be properly sized.

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Jim Phillips, P.E.
Brainfiller.com


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