fuse and wire sizing for multiple motors and other loads on 1 circuit

Tainted

Tainted

Senior Member
Location
New York
Occupation
Engineer (PE)
If I understand how to size wire and overcurrent protection if 1 circuit contains only motors. But what if it contains other loads like a heater for example.


Suppose I have one 25HP motor (74.8A FLC), one 10HP motor (30.8 FLC) and one 5kW heater (13.9A). All loads are continuous at 208V 3phase.

minimum wire size would be:

74.8(1.25) +30.8 + 13.9(1.25) = 141.7 amps -> 1/0 copper

Fuse size would be:

74.8(1.75) + 30.8 + 13.9(1.25) = 179amp ->175 amp fuse?

Since a heater is associated with the circuit, can we use 1/0 copper for the circuit or must it be 2/0?

is the calculation correct?
 
Last edited:
Feeder is 125% of largest plus 100% of others
93.5+44.7=138.2

Don't add the 25% of the heat load to either calculation.
Doesn't make any difference in the wire size or the fusing.
I believe you could increase the fuse size to 225 if needed. 430.53(C) Exception No. 2, (2)

Expect corrections
 
Tainted said:
Fuse size would be:

74.8(1.75) + 30.8 + 13.9(1.25) = 179amp ->175 amp fuse?
Click to expand...
Is this going to be a feeder? How are you providing overcurrent protection for each individual load? Are there going to be taps at each piece of equipment?
 
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