step up and step down Auto transformer

Thread Starter


Joined Oct 19, 2009

The link below is a FW-X240 Auto transformer stepup and stepdown.​x240.pdf

I looked on pdf file, I could not find which wire# is primary and secondary.
If it is step down, apply 240v on the winding# and will get 120v from another widnding. How do we verify which wires are used for step down voltage?




Joined Jun 29, 2011

The step down wiring is shown in section 1:9 of the manual. If you also look at the diagram on Section 1:5 it will show the colour codes for the transformer wires.


Joined Jul 9, 2011
I didn't get why they call it autotransformer, if it has two separate and equal windings.

But with this info

"Two identical windings:
• Winding one is between leads #1 and #2
• Winding two is between leads #3 and #4
• The start for each winding are on lead #1 and on lead #3"

and the drawing on page 6 you know at least how it was built.

1 and 3 is the beginning of each winding, so in their diagrams they connect 2 to 3. Doing so you put both windings in series.
So if you want a simple step-up you connect 2 and 3 and put your 120VAC between 1 and 2. Then you'll have 240VAC between 1 and 4. Or you connect 240VAC to 1 and 4 and will have 120VAC between 1 and 2 (and 3 and 4). Correct?
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