Question:

We received a tech call regarding an application to incorporate a manual starter and two contactors. The manual starter required a means of disconnect, short circuit protection and overload protection. The motor size was 20HP with an FLA of 23.4A @460V. The question from the customer was whether the KTA7-32S-29A, with a dial setting of 24-29A, was an appropriate selection for the application. The customer also asked if an overload incorporated to cover the actual full load rating on the motor would be a better choice.

Answer:

What was not clear about the application was “incorporate a manual starter and two contactors”. If there are two motors then it takes a short-circuit device and an overload relay for each motor. The original question indicated only one motor. If we assume one motor then one device is required as follows:

• In the field, someone’s first reaction might be to choose a KTA7-25S-25A based on the Current adjustment range of 18-25A, which fits within the motor FLA of 23.4. However, consider the following details:
  1. If the nameplate of a 20HP @ 460 Volt motor reads 23.4 FLA, then the FLA is the overriding selection factor. However, if you selected KTA7-25S-25A, an inspector may give you a hard time over the fact that the label says 15 HP @ 460 VAC, even though the government passed a law requiring the motor manufacturer to lower FLA to premium efficiency levels.
  2. Consider also that NEC 430-32 indicates for a 1.15 service factor motor that an overload relay trip at less than 125%. Consider further that Sprecher + Schuh overload relays are designed to trip at 120%. This means choosing KTA7-32S-29A with a 24…29A range with the dial set at 24A FLA setting represents a trip at 28.8, or 123% of 23.4 actual FLA. Therefore, choosing the KTA7-32S-29A unit with a dial setting at 24 Amps would be within the range.
• Perhaps more important to the application was that the manual starter required a means of “disconnect, short circuit protection and overload protection”. On page F5 of the Sprecher + Schuh Industrial Controls Catalog we indicate that KTA7-32S-29A is NOT a Self-Protected Combination Motor Starter (Type E) and therefore cannot be applied as the short-circuit device under NEC430-52.c.6
  1. Note that a manual motor starter cannot be used as a short-circuit device, but a Self-Protected Combination Motor Starter (Type E) can be applied as a short-circuit device under NEC430-52.c.6. Most of our KTA7s have both approvals but not all. Careful examination of the UL ratings application chart on F5 shows this.
  2. However, the KTA7-45H-32S is approved as a Self-Protected Combination Motor Starter (Type E), has a range of 23…32A, and has a 20 HP @ 460 VAC rating.

Our recommendation, barring the aforementioned need for clarification regarding the number of motors, was to incorporate the KTA7-45H-32A into the application. This means compliance with the HP rating and the FLA setting needed. The KTA7-45H-32A also provides short-circuit protection as a Type E rated device. There would be no need for a separate overload relay for one motor. Problem solved every way you look at it.

For additional information please contact your nearest authorized distributor, sales representative, or call our customer service or technical support lines.