Poor voltage to coil

Control voltage less than 85% during pick up may not be enough to safely close the

contactor and can cause the coil to meltdue to over heating. This because the coil

is designed to withstand the inrush current for a limited time only. One common

reason is when the coil supply is taken from the main supply were high current

is causing the voltage to drop. Too high continuous control voltage could also

cause the coil to melt. See picture below for typical failure.

Direct on line (across-the-line) motor starting.

Current peaks used by heavy duty starting- If the application requires a high level

of torque during start-up, for example a big fan or a pump, it is important that the

contactor’s making capacity and short time withstand current are capable of handling

the starting current and current peak.

Trouble shooting

examples of common reasons for contactors not working properly

Voltage drop during start up of the motor Voltage drop to less than 85 % of nominal

voltage for 5 to 10 ms can be enough for the contactor to start opening.

Also,other disturbances in the control voltage such as poor relay contacts or too small

control transformer/power supply could be responsible for this problem.

The result of these voltage problems can be increased

contact wear and also lead to welding of main contacts.

With the AF technology these problems are avoided.