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Thread: Transformer Question

  1. #1
    Join Date
    Jan 2015
    Kelowna, BC

    Default Transformer Question

    First time posting
    My house is hardwired for alarm system and my options are to put in a plug-in transformer (which I don't have an outlet close by) or to use a hard-wired transformer 16.5 VAC.
    The builders segregated one of the alarm wires (4-wire 22 AWG) and its right near an existing electrical box and door bell transformer 20V. Can I use that electrical box to wire in another transformer or can you have a transformer off of an existing transformer?? I am not too electrical savvy, but more or less want to know as I will need to order either a plug-in or hard-wired transformer and than likely get an electrician to do that part
    pic as well.Click image for larger version. 

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  2. #2


    You can most likely do it either way, and with the wall being open you have a lot of choices. It may be better to go with the hard wired transformer, and have the electrician add another round box just like the one in the picture. He'll have to run a short cable from the existing transformer box to the new one. He could just as easily put a box with a 120V receptacle off that circuit for you to use a plug in transformer, but there could be some code issues with that depending on what is powering this doorbell transformer (what else is on that circuit -- a receptacle may not be allowed).

    The doorbell would also probably work just fine at 16.5V, so you could maybe even just replace the existing doorbell transformer with a 16.5V one large enough to run the alarm and doorbell. But you may not be able to find that, and the alarm box may not be happy with the door bell ringers on that circuit. Safest thing is to run 2 separate transformers on the same circuit -- one for the doorbell and one for the alarm. Its just less efficient.
    Kent, WA

  3. #3
    Join Date
    Jan 2015
    Kelowna, BC


    Hey Mark,

    Thanks for the quick response. That helps me out a lot!

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