Article 430 Question

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Mustwin351

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If I have a 3 phase motor over 1 horsepower with thermal overload protection built into the motor do I still need overload protection for my branch circuit conductors being that my circuit breaker is sized 250% of full load current.


Or can I just rely on the overloads built into the motor to provide for the branch circuits overload protection?
 
Table 430.250

Table 430.250

If I am sizing my branch circuit conductors by utilizing table 430.250 to determine my motors full load current but my motor is 4hp is not listed on the table, do I then go off the 5hp rating on table 430.250 because that is the next size motor up?

It seems odd that your branch circuit doesn't need overload protection if it is contained within the motor but I guess it is acceptable because the equipment that my motor is in will be hardwired and not cord and plug connected.
 
Mustwin351 said:
If I am sizing my branch circuit conductors by utilizing table 430.250 to determine my motors full load current but my motor is 4hp is not listed on the table, do I then go off the 5hp rating on table 430.250 because that is the next size motor up?

It seems odd that your branch circuit doesn't need overload protection if it is contained within the motor but I guess it is acceptable because the equipment that my motor is in will be hardwired and not cord and plug connected.
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You could cross reference the FLA on the motor and see what size HP it is closest too.

Your branch circuit doesn't need overload protection because the thermal on the motor does that. It does need short circuit protection which is what the breaker or the fuse is for.
 
The motor nameplate tells me it is 4 hp but table 430.250 does not list a 4 hp motor so I assume I just use the next higher one up which would be 5 hp.
 
motor has temperture switch

motor has temperture switch

I think you are mistaking the motor thermal cutout with overload protection. The thermal that is in the motor is just an extra way of tripping the motor, If you waited for this the motor would be short lived. You need thermal protection at the starter on each phase to react to the load, then the ocpd does not have to protect the wire.
 
Mixing curcuits?

Mixing curcuits?

Mustwin351 said:
Or can I just rely on the overloads built into the motor to provide for the branch circuits overload protection?
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Are you talking about other things on the circuit besides the motor? If yes OCPD needs to be sized for the wire, but that may cause the circuit to trip from starting current of the motor. Unless it's another motor circuit I would not mix them.
 
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