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Another project with a switch...


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  • Another project with a switch...

    I need a dpdt momentary contact, center return switch for a 7A, 120V application. I can find exactly what I need at RS, but it's rated 20A, 12V. Can I still use it? It would, after all, use less amps....

  • #2
    It would be less amps, that's true. But a switch in an electric circuit is going to act like a small resistor, and the problem is that for a resistor, watts = volts times amps.

    So, you're going to potentially have 840 watts going through that switch as opposed to the 240 it's rated to handle, and that means there's going to be about 3 1/2 times as much heat generated by the current going through that switch. I don't know that the extra heat would be enough to harm the switch, tho.

    If I were you, I'd just see what a momentary DPDT switch rated at 120 volts and at least 7 amps would cost from your local electrical distributor, and base your decision on that. If you can buy a dozen Radio Shack switches for the cost of one from your electrical distributor, I'd be inclined to go cheap and see how long the RS switch lasts. If the prices are in the same ballpark, you'd be a fool to buy the RS switch.

    If you do go with the Radio Shack switch, maybe wear a rubber glove on your switch hand to protect you from an electrical shock until you get some confidence that the RS switch is going to last. That way, if the RS switch melts, you're not exposing yourself to as much danger.

    Also, if you're going to be using this project somewhere where you can't pull the plug quickly and easily (like on a ladder or a roof), you should consider adding two cheap wall switches, one in each circuit controlled by the DPDT switch. That way, if the RS switch does melt and the contacts stick together, you can shut the power off to the thing with the SPST switches.
    Last edited by Nestor; 04-26-2012, 10:37 PM.


    • #3

      a 12 volt switch cannot be used in a 120 volt application. its internals aren't built for the higher voltage. it all deals with insulation engineered into the switch. sometimes look on a circuit breaker. you'll see the abbreviation BIL. this is an industry standard for breakdown insulation value. Switches are rated by a "tungsten value" as to what voltage can be run through them. a G rated switch is general usage while a tungsten rated is for motor loads.


      • #4

        I would recommend you go to EURTON ELECTRIC to pick which switch you will use. All his switches are 120 and 240 volt rated.