Changing main contacts, arc chutes and coils

When changing the AF coil with its PCB (printed circuit board) care must be

taken to avoid ESD damage.

Before any dismantling of the contactor:Make dead by, turning off the contactor.

Opening the main circuit by turning off the main switch, if any, or by removing the

main fuses in all three phases. To protect against making attempt, open also the con

trol circuit.

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.