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Switch amp rating conversion

Discussion in 'General Electronics Discussion' started by doubledouble, Jul 16, 2013.

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  1. doubledouble


    Jul 16, 2013
    Hello all.

    I'm new here, just registered to be able to post my question. I'm in the process of planning to wire up a few accessories in my car. I need/plan to be using a SPDT switch as part of the project and am having some trouble finding an appropriate switch. I'll be wiring into a 15 amp fuse (could use a 10 A) and assume that I should use a switch that's rated for a higher amperage than the fuse that protects it - is this correct?

    Question 2; how can I calculate the rating for the switch in a DC circuit if the rating is given for an AC circuit? For example, I found one switch that looks like it would physically fit the location but the rating is 10A @ 125 VAC. Since I'll be using it in a 12 V DC circuit how can I calculate the rating - is there a simple formula for this? It seems to me that since the voltage is so much lower I should get higher amperage from the switch but the sales assistant at my local supply store thought it went the other way. Anyway, any help would be appreciated.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The switch should be rated for at least the normal current of the load (preferably more).

    If the load is up to about 7.5A, then the 125V 10A switch would be fine.

    For heavier loads it is typical to use a switch to control a relay which switches the load.

    Automotive relays capable of switching several tens of amps are common and relatively cheap. An equivalent switch would be large and you'd need to wire heavy(er) cables to it.
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