Overloads for Motors

[fifty60]

Is it a requirement that motors have overloads? I understand why motors have overloads. The branch OCPD is only providing short circuit protection, and without it there is absolutely no overload protection. I have a 1/2HP single phase motor that does not have an internal overload, and the question has been asked "I know I need one, but it is an absolute requirement that I have an overload."

I've explained the "why's" to them, but is there an NEC or NFPA79 code that absolutely requires it?

 

[fifty60]

I seem to remember reading that a single thermal magnetic circuit breaker could be used in place of the short circuit OCPD and separate overload....

 

[fifty60]

I've read through section III of article 430 (NEC 2011) and do not see the exception that allows you to use a single thermal-magnetic breaker or dual element fuse as short circuit AND overload protection....does this exception exist anywhere inside the code?

 

[david luchini]

I've read through section III of article 430 (NEC 2011) and do not see the exception that allows you to use a single thermal-magnetic breaker or dual element fuse as short circuit AND overload protection....does this exception exist anywhere inside the code?

Section III of Art 430 permits a "Separate Overload Device." This can be fuses or a circuit breaker. But keep in mind that there is no "next size up" rule for overload devices.

 

[fifty60]

So a dual element fuse or a thermal magnetic breaker would qualify, even though it would be serving the dual purpose of short circuit protection and overload protection?

 

[david luchini]

So a dual element fuse or a thermal magnetic breaker would qualify, even though it would be serving the dual purpose of short circuit protection and overload protection?

Yes, a fuse or circuit breaker could provide both functions.

 

[fifty60]

430.32(1) says "Motors with a marked temperature rise 40 C or less 125%". I would get this information from the insulation rating right? In this case it is Class F insulation. The temperature rise for this motor, with a 1.25 service factor, is much more than 40 C right? It would be closer to 115 C? Or would that not be the information that is being asked for in NEC 430.32(1)?

Also, I cannot tell if the "Motors marked with service factor 1.15 or greater" and "Motors with a marked temperature rise 40 C or less" are anded together, or if they are or'd. Since I know the service factor is 1.25, can I then ignore the temperature rise requirement for this particular clause?

I actually found the temperature rise in the data sheet. It is 67 C at rated load and 80 C at service factor load....this is above the 40 C, does that mean I have to size at 115% or can I size at 125% based on the "service factor greater than 1.15"...

 

[augie47]

The answer, IMO, is not a simple one. Details matter.
Possibilities: Is it Automatically started ? If so, 430.32(B)
For non-automatic start, see 430.32(D)
Is it on a General-Purpose branch circuit ? If so 430.42(A)
(which also directs you to G P circuit cord & plug connected 430.42C)

 

[fifty60]

It is an automatic start motor. It will be an air circulator motor inside of a refrigeration/oven chamber. Refrigeration equipment itself is not a general purpose equipement. Would the motor inside be considered a general purpose branch circuit inside a specific purpose application? I believe regardless, I am directed back to 430.32 (1). Service factor 1.25, temperature rise is above 40...is 125% rounded down permissible?

 

[texie]

The answer, IMO, is not a simple one. Details matter.
Possibilities: Is it Automatically started ? If so, 430.32(B)
For non-automatic start, see 430.32(D)
Is it on a General-Purpose branch circuit ? If so 430.42(A)
(which also directs you to G P circuit cord & plug connected 430.42C)

I agree. Especially when you are considering anything less than 1 HP. Above 1 HP things are a little more straight forward.

 

[fifty60]

I have it mostly figured out except for the fact that it is a 1.25 service factor motor, which allows 125% rounded down, but its temperature rise is above 40 C, so I would have to go to 1.15%. Is this "and" or "or"? Does the service factor of 1.25 alone allow 125% rounded down, or does the temp rise being above 40 C mandate then that I would have to use 115% rounded down?

 

[rlundsrud]

I know that they exist, but single phase motors that don't contain internal thermal protection are quite rare. Have you verified that this motor doesn't have this?

Bob

 

[david luchini]

I have it mostly figured out except for the fact that it is a 1.25 service factor motor, which allows 125% rounded down, but its temperature rise is above 40 C, so I would have to go to 1.15%. Is this "and" or "or"? Does the service factor of 1.25 alone allow 125% rounded down, or does the temp rise being above 40 C mandate then that I would have to use 115% rounded down?

I see it as an "or".

 

[augie47]

I see it as an "or".

me 2

 

[fifty60]

I believe it reads or as well. The motor does not have an internal overload, I am not sure why.