Calculation Question

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noeernlat

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Washington State
I need a little help understanding something here. I have a 3 phase 125A panel listed on the plans as being fed by 1 1-2" Conduit containing (4) 1AWG conductors and (1) 6AWG conductor. The calculated load for this panel is 14.8 Kva, if I'm correct this equates to a calculated load of 41 A. Now, I assume i have to derate due to 4 or more current carrying conductors which is 1 AWG (90deg Column) 150 X.80= 120A. Am I permitted to supply this gauge wire to a 125A panel even if the calculated load is 41A?? Im thinking I would need to run 1/0 Conductors. Thanks!
 
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skeshesh

Senior Member
Location
Los Angeles, Ca
41A is correct assuming a 120V/208Y panel. Are you sure you need to derate? In other words are you sure that the neutral should be counted as a CCC? If the majority of loads are non-linear then you are correct.
Is the panel rating 125A or does it actually have a 125A main? Whats the OCPD size upstream of this panel? You are allowed to size the conductor based on load so I'm assuming you're choosing a larger size to account for future loads and/or voltage drop.
Anyway, let's assume that you are correct about having 4 CCCs, and 90deg #1AWG, then the derated ampacity would be 120A. In that case you'll be able to able to use the next higher standard overcurrent device rating per 240.4(B) so you're ok. If the derating does not apply, you're still okay but you can choose a smaller cable and be fine.
 
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noeernlat

Member
Location
Washington State
skeshesh said:
41A is correct assuming a 120V/208Y panel. Are you sure you need to derate? In other words are you sure that the neutral should be counted as a CCC? If the majority of loads are non-linear then you are correct.
Is the panel rating 125A or does it actually have a 125A main? Whats the OCPD size upstream of this panel? You are allowed to size the conductor based on load so I'm assuming you're choosing a larger size to account for future loads and/or voltage drop.
Anyway, let's assume that you are correct about having 4 CCCs, and 90deg #1AWG, then the derated ampacity would be 120A. In that case you'll be able to able to use the next higher standard overcurrent device rating per 240.4(B) so you're ok. If the derating does not apply, you're still okay but you can choose a smaller cable and be fine.
Click to expand...

Yes, the majority of the loads are non linear. The Panel is a 125A MLO , and the OCPD upstream on the plans read 200AS/125AF (I dont know what this means). Thanks for your quick response.
 
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