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On a 120v primary / 24vac secondary transformer, how do you know which of the secondary wires are the common or the 24vac?

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Take your multi-meter and test each lead to ground.
The hot wire will show voltage.
The neutral will not show voltage.
Set multi-meter to 24V
Put one prong on wire, put other prong inside ground port on wall plug

On a 120v primary / - 0145983.jpg

Posted on Oct 08, 2010

  • ladle76266 Oct 08, 2010

    Conducted test with two different inexpensive auto-ranging multimeters and get 10vac on known common (orange lead out of transformer) and 8vac off 24vac lead (brown lead). Then conducted test with "good old" analogue Simpson meter and get the same 1/2 vac from either lead. Any other suggestions?

  • Anonymous Oct 09, 2010

    I was mistaken with my answer.
    My test was for DC transformer.
    When setting up electronic circuit, you use DC transformer.

    I think your test is accurate for AC transformers. There is no neutral back to ground because of how transformers work. The 120V AC runs through a coil, and the electric field from the first coil causes alternating current in a second coil. That would indicate both leads would show voltage to ground.

    What exactly are you using transformer for? Perhaps if you re-post with objective-defined, we might have some insight.

    I post similar questions on electronics forum:
    A lot of the helpers at electro-tech are looking for contract work building circuits



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