Using SSR for heated bed

  • What gauge wire should I use for signalling, to tell the SSR to turn the heated bed on?
    I am guessing it really doesn't matter because there will not be any load, but just asking to make sure I don't find out I was wrong the hard way.


  • I use 20 gauge, twisted pair. Twisting isn't entirely necessary, but it helps keep them neat. I twist them using a wire twister mounted on an electric drill.

  • I my plan was to use 14 gauge wire I had left over over for the heated bed itself, but it's over kill. Too thick for the signal screw side of the ssr. They don't fit into the crimped ends I have. I had some 18gauge solid wire to use temporarily until I buy something stranded but at the last minute I thought it may not be good enough.

    Thanks for the info! If 20 gauge works, 18 should be just fine.
    If I do use the 18gauge wire I may twist the wire as you suggested.

  • @mrehorstdmd what's wrong with putting the wires directly in the drill? I always did it like that. Screwing and unscrewing 4 screws takes much longer than the twisting 🙂

  • Twisting with a drill isn't a good idea. It puts stress on the strands. The wires in a true twisted pair are wrapped around each other like a braid, not rotated together. The cross section of each wire always maintains the same orientation.

  • @sigxcpu I used to do that and the wires would slip out of the chuck when I applied some tension as it was twisting. I use a lot of teflon insulated wire...

  • @gtj0 I get that, but twisting is better than not twisting, and the mechanism required to rotate the wires as they twist is considerably more complex and not nearly as easy to make.

  • I used something pretty small to control the SSR for my USA based 110/120V bed heater, I don't really remember, like 28, for about two meters total run. The printer is 1.5 meters tall, and there is a bit of horizontal to reach the board, etc.

    I didn't bother to twist. Nothing wrong with being twisted (ha)... but at several seconds per signal transition (bang bang) and almost no current... no real need either.

    Anyway, works fine.

  • administrators

    The current draw of the SSR control wires is a few tens of milliamps, so you can use thin wires. Just make sure they don't go anywhere near the AC mains voltage wires.

  • Ooops, typo, said "20" should have been "28", much smaller, now edited above.

    To repeat: I use 28 AWG wire for the signal side of the SSR, about two meters worth. Works great.

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