current capacity, voltage drop and short circuit level

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elicio

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Hi, i am Elicio, and i would like to make you a question about The National Electric Code.

I have 7.5 hp motor connected to MCC at 380 meters. The voltage system is 480V (Line to Line), maximun short circuit at the MCC is 39.55 MVA and i need to calculate the appropriate cable by tree methods, current capacity, voltage drop and short circuit level. I have already calculated this cable and is AWG #4. But i have a doubt, where do i have to calculate the short circuit ? at the motor?s connection or near the MCC.

The motor?s feeder is a continuous (1x3c #4 AWG) by tray and does not hace any connection betwen the ends.

regards
 
Re: current capacity, voltage drop and short circuit level

You could help us out in the backwards US by converting 380 m to feet and what is the fault current? I am not sure what 39 MVA is, is M = K or mega?
 
Re: current capacity, voltage drop and short circuit level

Not OP, but about 1235 feet.
 
Re: current capacity, voltage drop and short circuit level

Tom
Some times fault current is shown as MVA instead of amps. 39.5 MVA = 39500 kva = 40ka at 480 volts.
My cable manual shows #4 is good for about
17000 amps for 1 cycle. He will need to install a
CL fuse that will reduce the fault to something less that the 17ka for #4. I am assuming the 40 ka is on the secondary side of the transformer.
The voltage drop is 7 volts or 1.5%.

[ September 23, 2003, 09:03 PM: Message edited by: bob ]
 
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