General

In order to obtain satisfactory performance in any motor application, the first essential is to select the correct motor to meet the requirements of the driven machine. It is equally essential that a suitable starter should be used with the selected motor. Many will say that these are self-evident facts, but it is surprising how often the manufacturer is blamed for a faulty motor when the prime cause of the trouble is bad selection. It is also surprising how frequently the starter manufacturer hears the remark: 'The motor will not start ... the starter must be faulty'. An actual case occurred where a user purchased a two speed tapped wound motor, as it was the cheapest, and a starter for a double wound motor, again as it was the cheapest, and then complained that they would not work (tap wound motors have three contactors while double wound motors have two).

While this is an extreme case , similar instances occur all too frequently, illustrating in varying degrees a lack of appreciation of the factors involved. The first that is heard of the trouble is when either motor or starter manufacturer is blamed for supplying faulty equipment. The outcome is always the same - extra expense and delay while the correct equipment is being supplied.

This paper presents, as concisely as possible, a review of the prime factors in the selection of motor and starter (apart from the fundamentals of voltage, frequency and speed), with some reminders of various side issues which are sometimes overlooked