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ekstra   ara
 Post subject: The Table and Switchboards.
PostPosted: Wed Jul 01, 2009 6:13 pm 
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Joined: Thu Jan 10, 2008 8:49 pm
Posts: 483
Location: New England
The Table should have been constructed as a means to model typical US business industrial electrics.

"Panelboards or Switchboards Rated >240 and up 600V with molded case or insulated case circuit breakers - Note 1"

Note 1: Maximum or 25kA short circuit available, maximum 2 cycle fault clearing time.

Wouldn't you say that 25kA is atypically low? How many 480 switchboards are there in US businesses that are fed directly from the utility transformer which are often 1000KVA, 1500KVA, and even 2000KVA? Why would they pick such a low value?

Lets say we have something more typically industrial in the 35kA to 45kA range - what then. I take it we can't just use the 'switchgear' section whose footnote is max 65kA because it says 'power circuit breakers'.

What is the economical solution to deal with switchboards at industrial fault levels. I'm talking the classic Square D switchboard, main breaker compartment with attached I-Line distribution panel.

Further, lets say the fault is unders 25kA and there is a main circuit breaker. I think its safe to say that the utility is not using a primary fuse that will clear in 2 cycles for a secondary arc fault. So then we can't use the Table for the main. But if the main does clear under 2 cycles, can we use the Table on the distribution side of the cabinet? Is this prohibited because the fault on the load side of the main could carry over to the line side?


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