Multiple motors, single 240V ckt

[kenaslan]

I am considering connection having 4ea 1/3HP 240V motors on a single 30A 240V 2P circuit with 4 motor starters. The motor starters are FVNR Non-Fused Disconnect Combo starters. Starters will be fed with #10 XHHW. I believe that this is permissible per 430.32 (B).

 

[augie47]

IMO, you will run into problems with 430.52
Since your starters are non-fuse the 30 amp GFSC protection you propose would not offer protection of the smallest motor.

 

[jap]

IMO, you will run into problems with 430.52
Since your starters are non-fuse the 30 amp GFSC protection you propose would not offer protection of the smallest motor.

Can you expand on this?

Wouldn't the Overloads be protecting the amperage of the smallest motor?

JAP>

 

[augie47]

Overload protection appears to be covered. My comment is on Ground-Fault/Short Circuit protection per 430.52 which would allow a breaker 250% of the FLA of the smallest motor protected.. His 30 amp breaker exceeds that limit.

 

[jap]

Overload protection appears to be covered. My comment is on Ground-Fault/Short Circuit protection per 430.52 which would allow a breaker 250% of the FLA of the smallest motor protected.. His 30 amp breaker exceeds that limit.

I was looking at the Instantaneous Trip column but evidently it would exceed that also.


JAP>

 

[Fnewman]

I recently designed a similar system, but with fused disconnects for each motor in the circuit. Thermal protection for motors of that size is usually by embedded thermal overload.

 

[kwired]

430.53(A) would allow these motors to all be on a 20 amp breaker.

If it won't hold during starting, you have a problem, if they are PSC fan motors, it likely will hold, if they are high starting torque motors, it very well may not hold.

 

[Smart $]

Recommend getting fusible motor starters.