OCP on a MOV

[kenaslan]

I have 4ea 0.33hp MOV and 4ea 0.5hp MOV fed from a 50A branch ckt on #6AWG. Each MOV is tapped with a #12AWG to a 15A breaker. I believe that under Table 430.52 that I need smaller OCPD than the 15A. Any thoughts?

 

[Jraef]

I have 4ea 0.33hp MOV and 4ea 0.5hp MOV fed from a 50A branch ckt on #6AWG. Each MOV is tapped with a #12AWG to a 15A breaker. I believe that under Table 430.52 that I need smaller OCPD than the 15A. Any thoughts?

No, probably not. The OCPD needs to primarily protect the conductors, so no problem having a 15A CB on #12. The MOVs themselves are likely using what's referred to as "impedance protected" motors, meaning that if something goes wrong, they can run stalled virtually forever and not catch on fire, or at least until that 15A breaker clears. If not, they will either have their own internal thermal switch (aka "Klixon") or they would need to have a very specific label or instructions telling you that you need supplementary circuit protection and exactly what it needs to be. Every MOV that small that I've ever installed has been impedance protected though.

 

[topgone]

No, probably not. The OCPD needs to primarily protect the conductors, so no problem having a 15A CB on #12. The MOVs themselves are likely using what's referred to as "impedance protected" motors, meaning that if something goes wrong, they can run stalled virtually forever and not catch on fire, or at least until that 15A breaker clears. If not, they will either have their own internal thermal switch (aka "Klixon") or they would need to have a very specific label or instructions telling you that you need supplementary circuit protection and exactly what it needs to be. Every MOV that small that I've ever installed has been impedance protected though.

To add, most MOVs I got to tinker with are operated on a "torque limit" protection. Simply put, if the valve grinds to a halt, valve travel reaches max, or something prevents the MOV to proceed per control signal, the torque switch activates to stop the motor.

 

[kenaslan]

Thank you for your help

 

[Smart $]

Issues mentioned above are considered separate overload protection. The breaker rating you are questioning is considered short-circuit and ground-fault protection. Refer to 430.52 and it's exceptions. I find it quite common that electricians will reference a Table and forget to read the section text that actually says when and how to use its Table.