Single Phase Motors

[fifty60]

Why are most 3 phase motors safe to use in Class II Div II locations, and a lot of single phase motors are not? I understand that thermal overload protection needs to be external, but this can be done for single or 3 phase motors?

Is it the starting and/or run capacitor that is used in single phase motors?

 

[iwire]

Why are most 3 phase motors safe to use in Class II Div II locations, and a lot of single phase motors are not? I understand that thermal overload protection needs to be external, but this can be done for single or 3 phase motors?

Is it the starting and/or run capacitor that is used in single phase motors?

Total guess on my part but I imagine it is the start winding centrifugal switch built into the motor that could produce a spark.

 

[GoldDigger]

Is it the starting and/or run capacitor that is used in single phase motors?

Bingo!

More properly it is the contacts in the centrifugal starting switch internal to the motor.
If the single phase motor uses an external timer or other sensing circuit in the starter assembly to control the start winding (and that is in a protected enclosure or outside the classified area) then the winding itself would not be a problem.
If the motor is a shaded pole or other design that does not use a switched starting winding, then the justification is not there but the Code requirement may still be anyway.
With three phase motors the overload is also more likely to be outside the motor itself or the integral thermal protection contact will be a sealed temperature switch.

 

[fifty60]

What if it is dictated that only the fan blade is in the Class I Div II area. To make that kind of statement there is a whole can of worms opened regarding sealing this division, right?

Would a single phase PSC be appropriate if only the fan blade is in the hazardous (Class I Div II) area?

 

[GoldDigger]

What if it is dictated that only the fan blade is in the Class I Div II area. To make that kind of statement there is a whole can of worms opened regarding sealing this division, right?

Would a single phase PSC be appropriate if only the fan blade is in the hazardous (Class I Div II) area?

A PSC motor (Permanent Split Capacitor) motor has no centrifugal switch, so if the motor temperature does not exceed the classification limit and there is not an open contact temperature switch inside the motor, it could potentially be rated for Class I Div2 (Roman for Class, Arabic for Division).

The fan blade itself is not likely to be a problem unless it is a flint blade in a steel enclosure.

 

[fifty60]

Would I bimetallic strip be considered an "open contact temperature switch"? Would it all depend on how the bimetallic strip is sealed?

 

[GoldDigger]

Would I bimetallic strip be considered an "open contact temperature switch"? Would it all depend on how the bimetallic strip is sealed?

1. Probably
2. Yes.