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Explain the breakdown of the switch part number?

The 12 digit part number that begins with 4-7 is broken down and explained on page 5 of the SINPAC Catalog.

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How do I select a SINPAC switch for my motor?

1. Be sure switch series matches motor type (a single phase motor is a capacitor start only, or a capacitor start/capacitor run, or if the application is for an instant reversing motor).

2. Be sure switch voltage rating matches (start) circuit voltage rating.

3. Selection can be based on actual measurement of start capacitor current or two times the motor nameplate FLA rating.

4. Switch current rating must match or exceed the motor start capacitor current requirements. Always select a SINPAC Switch with the next higher current rating for:

  • High cycling applications.
  • Long acceleration time.
  • High ambients: Greater than 55° C.

5. To assure proper motor operation, the voltage across the start winding must reach the SINPAC Switch cut out voltage reference between 70% and 85% of motors synchronous speed.

Caution: SINPAC Switches are line voltage compensated. Changes in the line voltage will not affect system operation unless an overload condition causes reduced running speed, along with reduced voltage on the start winding.

6. Higher current switches can be used in place of lower rated switches of the same series.

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What is a cut out voltage and how is it measured?

Cut out voltage is the induced voltage across the motor start winding that is present when the motor rotational speed is near synchronous speed. This voltage is a combination of the start circuit line voltage, plus the built up voltage in the start capacitor. When the SINPAC Switch sees its rated cut-out voltage, it cuts the start winding out of the circuit. See instructions for measuring cut-out voltage at the center of page 16 of the current SINPAC Catalog.

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What is the duty cycle SINPAC switches can operate at?

This is dependent on actual switch used, current draw, ambient temperature, and time the switch is engaged - e.g., 3S or 1/2S. CV and VR switches have been tested at 2-3 cycles per minute under normal conditions. IR switches have been tested at 1 cycle per minute under normal conditions.

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Why won't my SINPAC switch work with my motor?

Reference the Stearns SINPAC Catalog, and assure that the proper switch has been selected based on Motor Horsepower, Motor Start Circuit voltage, full load motor amps, and proper cut-out voltage.

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