TEFC vs Open

[electricpete]

Looking around our plant I see several very similar motors (100hp, 3600 rpm) driving centrifugal pumps in similar environments (slightly humid, no corrosive chemicals, ambient <40C). All were spec'd and purchased in the 1980's and have class B insulation.

I doubt that we specifically asked for TEFC... since doesn't appear it was required by the environment. Is it possible that we left the choice open and the supplier supplied TEFC because it was cheaper?

Any thoughts?

 

[rhatcher]

Generally, TEFC is more expensive than an ODP motor of the same HP/speed. As well, for a given HP/speed, an ODP motor will (can) be one frame size smaller than a TEFC motor of the same rating.

As to why some of your applications are TEFC and some ODP when all else is the same....who knows? In general, my impression is that TEFC motors are more commonly produced now than ODP, where 25-30 years ago the opposite may have been true. If so, maybe you are seeing the transition period reflected in your equipment. Of course, that is not to say that ODP motors are not produced or used. In fact, (again an impression), these days the most common new applications that I see them in are by manufacturers of 'packaged' compressors and pumps. I believe that this is because of the smaller frame size and more so because of lower cost. (remember these are the same ones who usually size a motor to run at service factor...)

 

[jbartos]

Suggestion:
TEFC motors may be designed, based on some economical analysis, if some record shows that the light humidity is causing downtime, double-ended pipe ruptures damage open motors more than TEFC, and perhaps or habitually pumps and associated piping have traveling condensed water on pipes and other equipment, including debris, right into open motors.