Real World Learning

The article “Consider Motor Load Requirements & Applications,” by Cyndi Nyberg of the Electrical Apparatus Service Association (EASA) (pgs. 54-56, MAINTENANCE TECHNOLOGY, September 2007) brought the following comment from a reader in Wheeling, IL…

Dear Maintenance Technology:
The information (contained in the EASA article) is a good starting point; however, the load factor and power factor are important.

A fully loaded motor will have a good power factor and require no auxiliary equipment for power factor correction.

There are other conditions which contribute to the life of the motor:

1. Ambient temperature—If the air temperature is elevated, the cooling will not take place.

2. Starting and stopping—If it (the motor) is started and stopped several times an hour, the heat buildup is sizable.

Motors with a service factor (S.F.) of 1.0 run at full load have a relatively short life. Most applications for good power factor and long life should have an S.F. 1.15.

The E-plus motor would be a better selection as well as conserve energy. This would help reduce the amount of CO2 (or be another way to reduce the carbon foot print).

Arthur W. Ebeling
Retired
Via fax

We asked EASA to respond. Technical support specialists Tom Bishop, P.E., and Chuck Yung answered…

We appreciate Arthur Ebeling’s comments on Cyndi Nyburg’s motor load article in the September 2007 issue of Maintenance Technology.

We agree that load factor is important and that power factor can be an issue, especially when motors are operating below 50% of capacity. The main theme of the article is load factor, and the lower power factor (and, more importantly, efficiency) is specifically addressed. As for the need to provide auxiliary equipment to increase power factor, that is a seldom-necessary occurrence with EPAct and Premium Efficiency motors.

Ambient temperature is a factor in any motor application, if the NEMA standard 40 C limit is exceeded. Although the September article could have been expanded to address this, ambient temperatures above the NEMA limit would be an unusual condition and the topic would diverge from the focus of the article.

Starting and stopping capability of a motor is a significant condition and the article could have expanded into that topic. We appreciate that input and will keep that in mind for the future.

We do not agree that motors with a 1.0 service factor have relatively short lives. A motor that is properly selected and applied will provide a normal life span, whether it is 1.0 or 1.15 service factor. The service factor allows for periodic overload and does not in itself extend the life expectancy of a motor. The temperature rating of the insulation is a more important consideration, and most modern manufacturers use insulation at least one rating higher than the design operating temperature. Further, we know of no association of power factor with service factor.

…T.B. and C.Y.
(www.easa.org)