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 Post subject: What causes arc flash
PostPosted: Thu Oct 15, 2009 9:55 am 
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Joined: Mon Apr 14, 2008 7:10 am
Posts: 142
Can anyone explain why inadequate short circuit ratings will cause arc flash? In CSAZ462, it says that under normal operating conditions, enclosed energized equipment that has been properly installed and maintained is not likely to pose an arc flash hazard. The short circuit rating has no business with installation and maintenance. Thanks!


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PostPosted: Thu Oct 15, 2009 10:31 am 
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Location: Georgia
A device with inadequate short circuit ratings has not been properly installed (or the available fault current from the utility has increased). In a fault condition, the inadequate device could disintegrate and initiate an arc flash.


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PostPosted: Thu Oct 15, 2009 1:53 pm 
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Joined: Sun Aug 16, 2009 8:42 am
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Location: Lawrenceburg KY
JJH thats the way I understand it. Accidents happen. Noah, you may already know this part but for those out there I would explain the SCCR of a device and the importance as:

Along comes Joe a new guy and in a hurry to fix a blown fuse in equipment with high IE (incident energy) he unknowingly obtains an old component or a device rated with a very low SCCR from the stock room that is dark because of the power failure but it seems the same size. :eek:

Lets say he or she puts a fuse rated at 35 ka in a fused switch and the calculated short circuit current available is 100 ka and load side has a bolted fault across all three phases. :mad:

Turn the switch on. But I would have someone you really dislike turn on the switch.
Also, you may want to watch from a distance. The same applies to circuit breakers, motor starters, etc.

If the fuse blows and nothing happens it’s his or her lucky day.
If the door stays closed and does not blow open in flames they are even luckier.

But then again, it was not properly maintained, the family will miss that person. :( That’s why it’s important to know the SCCR of devices.

The internet has a few clips on devices not rated properly and exploding.

Noah, I believe this is not the answer you may be looking for but properly installed and maintained is true. Unless there is something that goes wrong.


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PostPosted: Fri Oct 16, 2009 6:06 am 
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Thank you very much! That is impressive!


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