Phasing Transformers

Thread Starter


Joined Dec 5, 2006
Wondering if anyone has a quick and easy way (no Osciliscope) to phase two step down transformers. 120 VAC to 24 VAC low voltage HVAC control application. Please advise of any methods you have found as well as any tools that you recommend. Keep in mind most control installers or technicians do not have Osciliscopes, typically lucky to have a VOM.


Joined Apr 26, 2005
Most would follow the wiring diagram found in the technical documentation that came with the HVAC.

If you have the diagram, post it. I really don't think it matters other that you have the 110 side connected to 110 and the 24 side connected to 24.


Joined Apr 20, 2004

Which side do you need to phase? If it's the output, look between a lead on one secondary and one on the other. If your meter reads 0 volts, they are in phase.


Joined Nov 21, 2006
I agree with beenthere
Isolate ALL secondary leads before proceeding with following.
Connect primary leads of both transformers to the same source.
Connect one lead of your voltmeter to either secondary lead of transfomer #1. (It would help to identifiy this lead with some tape etc.)
Using the other lead of your voltmeter, check BOTH secondary leads of
transfomer #2. The lead that measures 0 volts is the "mate" to the chosen lead of transformer #1. Be sure to mark the lead of transformer #2 that tested 0 volts so you don't get them confused later. I don't know the va capacity of the transformers you are working with, but getting the leads
"bucked" could be a very unpleasant experience.
Hope this helps.