460V/3phase Motor NEC Requirements

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jesteban

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I have a 460v/6.6amps/3 phase motor
1) What amperage rating should my Circuit Breaker have?
2) What should be the size of my Fused Disconnect for each phase?

here is the full motor info: It will be wire for 460
HP: 5
Voltage: 208-230/460
Hertz: 60
Phase: 3
Full Load Amps: 15.4-14.2/7.1
Usable at 208 Volts: N/A
RPM: 1750
Frame Size: 184T
Service Factor: 1.15
Rating: 40C AMB-CONT
Locked Rotor Code: K
NEMA Design Code: B
Insulation Class: F
Full Load Efficiency: 87.5
Power Factor: 75
Enclosure: TEFC
Mounting: F1
 
Last edited:
Not enough info

Not enough info

We need to know the horsepower of this motor to answer your question. Nameplate information is used for OL only!
Thanks,
Fran
 
Here is the full info on the motor: it will be wire for 460V

HP: 5
Voltage: 208-230/460
Hertz: 60
Phase: 3
Full Load Amps: 15.4-14.2/7.1
Usable at 208 Volts: N/A
RPM: 1750
Frame Size: 184T
Service Factor: 1.15
Rating: 40C AMB-CONT
Locked Rotor Code: K
NEMA Design Code: B
Insulation Class: F
Full Load Efficiency: 87.5
Power Factor: 75
Enclosure: TEFC
Mounting: F1
 
5 HP 460 Volt = 7.6 A

OCPD
7.6A X 175% = 13.3 A (Minimum size)
Round this up to the next standard fuse = 15 Amps (Standard size) 7.6A X 225% = 17.1 A (Maximum size)
Round Down for the standard size fuse = 15 Amps
In this case both the standard size and the maximum would be the same size.

Overload
7.6 A X 115% = 8.74
Round down and start with a 6 Amp fuse.
 
FrancisDoody said:
5 HP 460 Volt = 7.6 A
Click to expand...

for a standard 5 HP motor, via the 430.150 table, right ? However:

jesteban said:
Voltage: 208-230/460
Full Load Amps: 15.4-14.2/7.1
Click to expand...

Motor nameplate FLA is 7.1 so I would use that. And I mostly use class CC fuses that let me go up to 300% size, if needed.
 
Change your calculation

Change your calculation

Name plate information is used strictly for overload calculations. The table you are referring to corresponds to the 2002 NEC. I believe the table has a different number in the 2005 NEC. Maybe 430.250 Full-Load Current, Three-Phase Alternating-Current Motors.
 
FrancisDoody said:
5 HP 460 Volt = 7.6 A

Overload
7.6 A X 115% = 8.74
Round down and start with a 6 Amp fuse.
Click to expand...


How long will a 7.6 amp load run on a 6 amp fuse?
 
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