Setting the motor protection on a submersible pump
The overcurrent release integrated into the motor-protection switch must trip on cold start in less than 10 seconds at five times the maximum motor current stamped on the rating plate.
In order to provide the best possible protection to the submersible motor, the motor-protective switch should be set in accordance with the following guidelines:
1. Set overcurrent release to the stamped maximum motor current.
2. Let the pump run for half an hour at normal power.
3. Set the overcurrent release successively lower until the trip point is reached.
4. After that, set the overcurrent release 5% above this trip point.
If the tripping characteristic of the motor-protection switch does not fulfil these requirements, the motor warranty is void. The maximum adjustment value of the overcurrent release must not exceed the maximum motor current stamped on the rating plate. For motors wound for star-delta start-up, proceed as follows when setting the motor-protection switch, but note that the protective switch setting must not exceed a maximum value of:
Protective switch setting = stamped max. current x 0.58.
The maximum permissible start-up time for star-delta starters or for motor switches with autotransformers is 2 seconds.
Grundfos offers different devices for motor protection like the MP204 module, for further information, refer to CAPS.