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I am trying to place both germicidal lamps (approx 70 watts total) and a negative ion generator in my air condition return space where the blower motor is.

My fist advice was to run these two devices off one 120 volt plug where each of these devices could be plugged into. This was a perfect idea, I thought, because the HVAC relay that controls the blower motor could also switch these 2 devices on when the blower was blowing. I found later that the motor is running on 240 volt with a red wire (not connected) for a low speed on the motor.

Is there anyway to convert the plug that I accidentally wired with 240 volts to 120v or run a 120 volt plug from the 240 volt plug. I can't figure out how to get a neutral from the 240 volt plug. I could still use this 240 volt plug for my ozone generator which requires 240 volts.

Would it maybe be best to run a whole new 120 volt plug circuit and use a 24v/120v relay from the thermostat wire to turn this box on and off with the blower motor?

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    Are you saying there is 240 on a 120 plug? Or did it look like 120 with a sideways blade? In that case there will be hot hot ground no 120 possible a new circuit will be needed unless the furnace itself is 4 wire hot,hot, neutral & ground, then 120 may be possible.
    – Ed Beal
    Commented Jul 26, 2022 at 20:29
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    If you only have hot, hot, plus ground now(common for 240), you need a new circuit for 120 volts. Are the plugs three or four prong/holes?
    – crip659
    Commented Jul 26, 2022 at 20:29
  • one word, relays
    – manassehkatz-Moving 2 Codidact
    Commented Jul 26, 2022 at 20:39
  • Well, you could always use a transformer. Not a cruddy step-up/down transformer from Amazon, a proper 120/240 isolating transformer.
    – Harper - Reinstate Monica
    Commented Jul 27, 2022 at 5:18

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It is probably easiest to do what you say in your last statement: Run a new 120V cable and control it from a new relay, controlled by the same thermostat signal as the blower.

If there is an unused neutral in the cable feeding the blower (make sure it's connected at the panel), you could use that to power the new gadgets using either of the live wires , but you still need a new relay. The reason for that is the existing relay will disconnect the two live legs from each other but will not disconnect either of them from its source, so there is nowhere you can tap off of the existing relay that is "off" in relation to your neutral.

If you do run a new 120V cable, it doesn't have to be from the panel, it could be from the nearest available junction box on an existing circuit. But you should install a manual cutoff switch outside the blower housing, next to the blower's one, to make it clear to people doing maintenance that both must be shut off before servicing. It would be safer to use one of the existing live legs but if you don't have a neutral that would require replacing the existing feed cable with a /3 one.

I may be wrong, I'm making assumptions. If you upload the wiring diagram for your blower and add it to the question and a picture of the relay, that would help to confirm this.

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