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Reduce 120v house current to 12v heat recovery ventilator

  1. Nov 4, 2014 #1
    We had a heat recovery ventilator that was controlled by a mechanical timer connected to a 120 v line (the line has its own breaker in the electrical panel and is also connected to a few lights and plugs) in each of three bathrooms. The 120v line is connected to a metal electrical box marked as a relay, that was then connected to the HRV with some thin brown wiring that comes from the relay. We have installed a new HRV and the heating contractor has indicated that he cannot connect the 120v line timers to the new HRV as the connections must be 12v. He wants to pull new 12v wiring from each of the three bathrooms (not a simple or inexpensive project in a two story house).

    I am not convinced that the brown wire coming out of the relay is not 12v (the line going in is a thick white cable). Is it possible that the metal box marked by the original electrican as a relay (which would open or close the circut when one of the three timers was activated) also acts as a step down converter as well? Is there any simple way to determine this?

  2. jcsd
  3. Nov 4, 2014 #2


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    Science Advisor

    Yes very possible.

    With a meter. That probably would've been the first thing the electrician did.

    I'm not sure why new cables need to be run. I used to install HRV's but don't understand your situation. In my country you wouldn't run new cables for 12v controls if there were existing (now unused) mains voltage cables already installed. the new HRV would be controlled with the same cables the last one was.
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