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kentannenbaum 12-27-2010 08:29 AM

single-pole double-throw switch
I just ran a 12-3 line for 240v baseboard heaters and now want to use one of those lines for an A/C in the same room during the summer. The switch is really expensive, but is there anything wrong with using an in-line SPDT 20amp switch that CLEARLY would cut half the power to the heaters during the summer only? The switch has center "off" position and two "on" positions to channel current one way or the other. Thanks.

kok328 12-27-2010 01:44 PM

Is the A/C 120V or 240V?

If 120V, where you getting your neutral & ground from?

To the best of my knowledge a SPDT will cut both legs of power in a 2-pole circuit.

kentannenbaum 12-27-2010 02:49 PM

This is a 12/3 cable. My plan for the 120v A/C WAS to use the white wire as neutral and of course the copper as ground AND to use the SPDT to split one of the hot wires which goes to the baseboards in winter and use that "split off" leg for the 120v A/C in summer.
BUT, I decided to run a dedicated 12/2 cable to the A/C which doesn't exist yet. Too bad I didn't think to go to an electric supply house a use 12/4. Would have saved a lot of time. Again thanks.

JoeD 12-28-2010 08:54 AM


Originally Posted by kok328 (Post 52466)
To the best of my knowledge a SPDT will cut both legs of power in a 2-pole circuit.

SPDT = Single pole double throw. Single pole means it only cuts on leg.
If you want to cut both legs you need a DPDT.Double pole double throw.

Not sure how the code feels on this but a normal three way switch could work. Put one hot on the common and the heater on one traveller and the AC on the other traveller. Only one device will be able to be on at any time.

speedy petey 12-29-2010 09:17 AM

What happened, you got tired of this? SPDT double-throw switch

LOL :p

ajaynejr 01-27-2011 09:07 PM

An ordinary 3 way switch is a single pole double throw switch.

Be sure that the switch current rating is sufficient before using it to control a heater.

kentannenbaum 01-28-2011 04:59 AM

Actually, I decided to run another separate line for the A/C. Thanks very much for the insight.

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