9)Milivolt drop test

• Checking mV drop with an accurate meter which indicates< 0.2mV when shorted

• Twist the connecting leads while measuring to avoid false pick ups

• Measure current with clip on meter

• The values of drop measured should be less than 4.0mV at the rated current of contactor for AC3 duty. mV volt drop can be calculated by given formula:


Milivolt drop test



Corrective action: If milivolt drop is more, then it is indication of bad joints

For case A & B) Clean the surfaces, apply Dowells crimping compound & re-crimp cables



Image A




Image b




For case C) Higher value of mV drop in this case could be due to either case A or B; In case of persistent higher value, replacement of the entire contactor is necessary


Image C


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