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 Post subject: table ?
PostPosted: Sun Nov 07, 2010 3:47 am 

Joined: Sun Nov 16, 2008 12:01 pm
Posts: 44
We are instructed to use the tables in 70e @ work , our ppe is 2*. To do a task for work in a mcc 480 volt and a note 2 is listed for the max of 65ka scc available; max of 0.03sec. clearing time.

How can we perform this task if we do not know how to determine kaic and clearing time? We just found out in a forum that the ka rating listed on the 800 amp breaker has nothing to do with the kaic or clearing time. Does this mean all
energized work such as troubleshooting is off limits ? Can work such as loto be done on any of the buckets in the mcc ? Would knowing the kaic and clearing time of the main be enough to work in the mcc ?


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PostPosted: Sun Nov 07, 2010 7:28 am 
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Joined: Wed May 07, 2008 5:00 pm
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Location: Rutland, VT
That is true that the kaic rating on the breaker and associated equipment (MCC, panel, etc) has nothing to do with the actual available fault current. The rating on the breaker/equipment provides information that the equipment will safely handle a bolted fault up to that rating. This related to the ability of the equipment to withstand the mechanical forces of a bolted fault.

All that being said, you at least need to determine the available fault current and associated clearing time at the equipment that you are working on to be able to use the tables. You need to have an electrical engineer determine this.

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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