Subpanel feed calculation.

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tomleveq

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Help!
????? Myself and another electrician are at odds about the cable size for a
subpanel. I want to feed 60amps to a subpanel 75 feet away from the Main
panel. What size SER (AL)cable should I use? Do I only need to use the 75
degree column (310.16)along with the 3% VD for calculating?

Thank you very much,
 
Re: Subpanel feed calculation.

I doubt voltage drop will be too much of a problem at 75 feet and only 60A of current-carrying capactity. Limiting to 3% should be obtainable without going to a larger size conductor than required per 310.16.

Follow 110.14(C) to determine which temperature rating to use for your conductor size. The voltage drop of #4 AL at 75 degrees will only be 4.5 volts assuming the 21.2 for K and a connected voltage of 240V.
 
Re: Subpanel feed calculation.

Still a little confused after reading 110.14(C).
Must I still use the 60 degree column if the terminations are rated for 75 degrees? Can I only bring 50amps instead of 60 to the sub?
Thank you very much,
 
Re: Subpanel feed calculation.

If all your terminations are rated at 75 degrees, then you can use the 75 degree column. Obviously you must use the 60 degree column for types TW, UF and NM cable.

The feeder rating to the sub-panel must be sized large enough to carry the load to be served but can't be larger than the rating of the panelboard.
 
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