FAQ01609 of Measuring / Motor Protective Relays FAQ

When the operation lock button is pressed, the input to the relay level detection circuit is forced to zero (0) and the time counter for time-limit operations is reset. (Instantaneous elements are not locked.) Use this function for the following purposes.

1.To prevent the time-limit element from operating in advance while measuring the instantaneous operation current.

2.When measuring the operating time for the time-limit element with a stop watch or similar instrument.
Apply the desired overcurrent with the operation lock button pressed, then start the counter (stop watch) at the point where you release the operation lock, and stop the counter (stop watch) when the indication appears.

Note:Perform the measurement quickly. If an overcurrent is continuously applied for an extended period of time with the operation lock button pressed, the current transformer (CT) may be damaged from burning.

Location of the Operation Lock Button
Side with the Nameplate