Isc Current for Panel Boards / SwitchBoards / Urgent Final request??

[EDISON_NY]

Could you please help me to solve these 2 questions; I did try different ways and got different answers, just want to find where is my mistake:

1) Service panel served from 100 KVA, 1ph, 2% impedance with 1/0 AWG conductor, 50' away, what is the max fault current at panel?

2) 1000A switchboard rated 480V, 3ph, 60 Hz, served from 1000KVA, 3ph, 5% padmounted xfrm, using 3 sets of 400 kcmil copper in non-metallic conduit, 100' away. What is the max fault current at Panel?

Thank you in advance.

 

[EDISON_NY]

Any comments!!!!

 

[Dolphin P.E.]

1) You haven't provide the voltage or the conduit type. Assuming the line voltage is 480V, and the wire runs in steel conduit.

Short Circuit KVA for transformer = 100 / 0.02 = 5000 KVA

Short Circuit for feeder = (480 * 480) / (1000 * 0.00275) = 83780 KVA (note: 0.00275 is the value of the 50ft feeder reactance from NEC table 9. )

Resultant KVA short circuit = (5000*83780)/(5000+83780) = 4718 KVA

Max Short Circuit Current = 4718 / 480 = 9.8 KA

Next KAIC panel rating available is 10 KAIC

2) Same method as above.

Short Circuit KVA for transformer = 1000 / 0.05 = 20000 KVA =20 MVA

Short Circuit for Feeder = (0.48 * 0. 48) / (0.00163)= 141 MVA (Note: 0.00163 is the value of the 100 ft , 3 set of feeder from NEC table 9)

Resultant MVA Short Circuit = (20 * 141) / (2 + 141) = 17.52 MVA

Short Circuit Current = (17.52 * 1000) / (480 * 1.732 ) = 21KA

Next KAIC panel rating available is 22 KAIC.

I hope it will help.

 

[vdubEE]

I was hoping someone would answer this as I was interested and have not run across problems like this. While I don't think we will have to size panels for the PE, the calculations that could pop up. Thanks, Dolphin.

 

[EDISON_NY]

Thanks Dolphin P.E. ,

 

[Mahmoud]

where did you find the next Panel size (KA Rating)? which standard you are looking at ?

 

[Dolphin P.E.]

KAIC standard depends on the manufacturer, for example 'Square D' has10K, 14K, 18K, 22K, 25K, 35K, 42K, 65K, 100K, and 200K just for 120/208V panelboards.