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Old 08-07-18, 07:39 AM   #5
jeff5may
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If you're running low voltage (24vdc or less), contact arcing is less of a problem and regular AC rated contactors can work. Once the voltage goes up above about 50vdc, the contactors with magnets inside must be used. When the switch contacts open, the magnets repel the arc and blow it out. AC contacts tend to either weld to each other or vaporize in short order trying to do their job with high voltage DC. The more current run through the switch, the faster the arc welding process occurs. I try to get a magnet contactor rated about 50 percent over the circuit breaker amps.

Then again you could use a solid state device. They operate silently and for many more cycles than a mechanical contactor. I try to get double the voltage and current ratings in the specs on the label. The things tend to run cooler and handle blips and spikes without failing immediately.
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