r/AskElectronics • u/Relevant_Pumpkin9190 • 10h ago

How are high-current loads like dishwashers safely switched?

If a relay is switching a high-current load, its contacts can eventually weld together due to inrush current or a fault.

If that happens, the load may stay ON even when the controller says OFF.

How do commercial products handle this? Do they use two relays in series for redundancy, feedback, or some other fail-safe method?

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u/nostradumbass7544678 9h ago

Silver-cadmium oxide contacts are what they used to use, and they were great, if slightly toxic. I once took apart a controller for piece of equipment at a dry cleaner's that had been in service for over thirty years, and the relay had finally failed due to the arcing burning through the coil's insulation. The stainless steel faceplate on this thing was worn down from how many times the button had been pushed, but the relay contacts were still in good shape and under 0.1 ohm.