Feeder taps / OCPD for AC units?

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cppoly

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Something I noticed in article 440, is that there is no section for feeder size or feeder short circuit and ground fault protection the same way it is shown in article 430 for motors. Does this mean it's not allowed to feed two AC units from one OCPD and tapping off to provide individual branch circuit protection?

For instance, if I have an AC #1 at 121 FLA / 175A max fuse and AC #2 at 57 FLA / 80A max fuse. Would you be allowed to feed them from one fused switch, then tap off to 175A fuses and 80A fuses for branch circuit protection? What feeder fuse size would you give?

If you were following article 430 for the feeder fuse, it would be 175A (largest unit fuse) + 57A (running amps of remaining units) = 232A, then round down to 225A.
 
david luchini

david luchini

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cppoly said:
Something I noticed in article 440, is that there is no section for feeder size or feeder short circuit and ground fault protection the same way it is shown in article 430 for motors.
Click to expand...
See 440.3(A)
cppoly said:
If you were following article 430 for the feeder fuse, it would be 175A (largest unit fuse) + 57A (running amps of remaining units) = 232A, then round down to 225A.
Click to expand...
430 doesn't tell you to use the largest unit fuse size, it tells you the use the largest compressor (or largest motor) maximum fuse size.
 
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cppoly

Senior Member
Location
New York
How would you apply 430 to pre-packed AC equipment? For these AC units, the manufacturer gives the max fuse size for the whole unit. In a similar fashion to 430, would you simply take the largest motor (in this case the largest AC unit max fuse listed on the equipment) + the remaining motor FLAs (in this case the remaining AC unit FLAs listed on the equipment) then round down?

Per my example, that would be 175A max fuse size for AC #1 + 57A FLA for AC #2, then round down.

OR, for AC units, are you suggesting to use the largest motor compressor fuse size + the remaining motor FLAs, then round down?
 
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