Technical Tips & FAQs

CEP7 Overload Relay test procedures

QUESTION: What procedure can be used to test the phase loss or overload protection on a CEP7 overload relay?

ANSWER: Our normal production test procedure is not something that a customer could easily duplicate. However, a basic on-site test can be run following the examples below (assuming that the motor is not running at the minimum FLA of the overload):

Overload Protection Test:

  1. Measure the normal motor running current (i motor).
  2. Turn off the motor and let it cool for about 10 minutes.
  3. Calculate the following ratio: i (motor) / i (overload min FLA). 
    For example, if i (motor) = 3.0A, and the customer is using a 1-5A overload, i (overload min FLA) is 1 and the ratio is 3.  If the ratio is less than 1.2, this test cannot be run.  For best results the shortest test times are obtained when the ratio is 2.0 or greater.
  4. Set the overload to its minimum FLA and turn on the motor.
  5. Wait for the overload to trip.  The trip time should be within the range defined by the trip curves on the overload instruction sheet for the ratio calculated.  The trip time should be close to the cold trip time defined on the curves as shown on the CEP7 instruction sheet.

Phase Loss Test:

If a phase loss test is desired, the customer may install a suitably-rated normally closed (NC) contact block or NC contactor in series with one of the motor phases. To run the test perform the following steps:

  1. Turn the FLA dial back to its proper setting and let the motor run for at least 5 minutes
  2. Open the contact(or) while the motor is running and start a timer
  3. The overload should trip in around 3 seconds, or within 10 seconds maximum. In order to prevent damage to the motor, under no circumstances should the customer simulate a phase loss in this manner for longer than 10 seconds.

The CEP7 phase loss detection is designed to operate under the following conditions:

Other important items to make note of for a Phase Loss testing procedures are the following:

In order to guarantee that both of these conditions are met, it is a good idea to run the motor at (or near) 100% of the overload FLA setting for about 5 minutes or more before running the phase loss test. If you do this, the overload will trip for phase loss in about 3 seconds. Conversely, if you try to run a phase loss test on a "cold" overload, you will find that it will take a while, perhaps 1 to 2 minutes worst case, because of the need to satisfy the conditions noted above.

September 2017

Jason McCoy

Jason McCoy, Product Manager

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