430.32(A)(1) vs (A)(2)

[George Stolz]

Why do thermal protectors have a different value than separate overloads?

Also, are thermal protectors ever field chosen and installed?

 

[Smart $]

Why do thermal protectors have a different value than separate overloads?

I'm guessing because it is a more direct measurement of motor temperature. Never really thought about it much. Actually I have to wonder how you determine the trip current level. Thermal protectors are based on temperature, not current... right? Yes they are related, but say a motor has an integral thermal protector whichs trips at X degrees. I'm sure someone has a conversion table somewhere )

How would one demonstrate compliance with the NEC???

Also, are thermal protectors ever field chosen and installed?

In my experience, not for new motors... but my experience is probably by far very limited compared to other patrons here.

 

[iceworm]

Why do thermal protectors have a different value than separate overloads?

Also, are thermal protectors ever field chosen and installed?

My response is not to be taken as all inclusive - just one person's anecdotal experience. Note to nit pickers - yes, I am certain there are many exceptions to my comments.

About the only motors I have seen with integral thermal protectors are single phase like tablesaws, aircompressors, oil-fired furnace guns, or blower motors, or submersible pumps in service station fuel tanks. An exception is 3ph submersible pumps is refueling systems. The submersible pumps have thermal cutouts to shut them off if the pump suctions are dry - the pumps are fluid lubricated and the motors are fluid cooled.

I suspect the single phase tablesaw (and others) type of applications have motors with integral thermal protectors cause it is a dollar cheaper that having to put in a thermal overload switch.

In either case, separate overload or integral, the point is to prevent a fire not really save the motor.

How did the code panel select the currents for integral thermal portectors? Probably the same method use for some of the other numbers given (25 ohms comes to mind). I'd guess either blindfolded dart boad, or ouiji board.

ice