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 Post subject: SKM PTW Miscoordination
PostPosted: Mon Feb 02, 2009 11:30 am 

Joined: Wed Nov 12, 2008 10:26 am
Posts: 46
Location: CA
Miscoordination is not necessarily a bad thing.

I struggled to eliminate miscoordination errors from my Arc Flash Studies until I spoke with Jim Babcock at SKM. Jim teaches their Arc Flash seminars.

Traditional protective relay studies are based on Isc, three phase bolted fault currents. In reality most real life faults are less than Isc, especially arcing faults. IEEE 1584 uses 85% of Isc. NFPA 70E uses 38% of Isc.

What the "(*N5) Miscoordination, Upstream Device Tripped" message indicates is that an upstream device (fuse or relay/CB combination) interrupts the fault before the device closest to the faulted bus. That's good, compared to not clearing the fault at all. It's a situation you may want to address with your protective relay specialist. There may not be a perfect solution that properly protects for both Isc and arcing faults.


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PostPosted: Thu Feb 05, 2009 6:48 am 
Sparks Level

Joined: Mon Apr 14, 2008 7:10 am
Posts: 142
Thanks for sharing!


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PostPosted: Thu Feb 05, 2009 9:05 am 
Sparks Level

Joined: Thu Oct 18, 2007 7:10 pm
Posts: 263
Location: NW USA
Nice to have a reality check.

Because we are calculation for worse case exposure it is compelling to get swept up in worse case fault thinking which may not be realistic.


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