Breaker size?

[anbm]

We have a fan power box with 5kW (6.01 FLA) electric heat, 1/2HP (1.1 FLA) fan motor, 460V/3PH.
Mechanical schedule calls for 15A/3P current protection for this unit.
We had a spare 20A/3P breaker in existing 480V panel,
can we feed this unit from 20A breaker instead of
adding new 15A breaker in the panel? Any code violations
if using 20A breaker?

 

[hillbilly1]

Use a fusible disconnect with 15 amp fuses at the unit, problem solved.

 

[anbm]

Use a fusible disconnect with 15 amp fuses at the unit, problem solved.

Will it costs less to install 15A fused disconnect at the unit vs. adding new 15A breaker in panel?
(panel AIC rating is 42kAIC)

 

[augie47]

Normally you should have a manufacturer nameplate providing the MCA and MOCP.
Without that, IMO, you would be limited to the 15 amp breaker due to the rules of 430.52.
(unless of course you do as hillbilly suggest and add a fusible disconnect)

 

[hillbilly1]

Will it costs less to install 15A fused disconnect at the unit vs. adding new 15A breaker in panel?
(panel AIC rating is 42kAIC)

You have to install a disconnect anyway, upgrade to a fusible and fuses, unless one is built into the unit, if you change the breaker, a shutdown would have to be scheduled, is the building already occupied? Or still under the construction phase?

 

[anbm]

You have to install a disconnect anyway, upgrade to a fusible and fuses, unless one is built into the unit, if you change the breaker, a shutdown would have to be scheduled, is the building already occupied? Or still under the construction phase?

under construction and we had non-fused disc. at the unit

 

[infinity]

Either way you need a 15 amp OCPD. Just figure out which method is the cheapest.

 

[Jraef]

What controls the fan motor? Is it just a motor starter or is it a combination motor starter with it's own fuses or CB?
Have you run the wire yet? If it's already run with 14ga, you cannot put a 20A breaker there to protect that circuit.