Single Phase Transformer 480V to 120V

Doug1984December 31, 2011

I have a square D single phase 1.5KVA dry transformer and I am hoping to get a thumbs up before I energize it. It has 8 wires - H1,H2,H3,H4,X1,X2,X3,X4. It is obvious from the tag that the incoming 480V connects to H1 and H4 and the outgoing 120V is connected to X1 and X4. The rest of the wiring is confusing. I wire nutted H2 and H3 together.

I took X3 and wire nutted it with X1 and the red Hot wire to my panel. I wire nutted X4, X2 and the white neutral wire to my panel.

Thumbs up or down?

This is an identical tag as on mine

http://cgi.ebay.com/ws/eBayISAPI.dll?VISuperSize&item=270817811556

Here is a link that might be useful: Picture of Identical Tag on Transformer

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Ron Natalie

No!
Correct, to run 480 primary, you connect H2 and H3. If you are going to run a 230 primary you'd connect H1 to H2 and H3 to H4.

Similarly, if you want the secondary at 240, you connect X2 and X3.
If you want 120, you connect X1 to X2, and X3 to X4.

    Bookmark   December 31, 2011 at 9:09PM
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bus_driver

I think that Doug has it correct.

    Bookmark   December 31, 2011 at 9:51PM
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brickeyee

It should all be on the nameplate of the transformer.

Many even have tables of what connections for input and output combinations he transformer can provide/accept.

    Bookmark   January 1, 2012 at 10:37AM
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Ron Natalie

He has the primary correct, he needs to do the secondary as I stated.

    Bookmark   January 1, 2012 at 10:17PM
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Doug1984

I think Ronnatalie is right - I'll wirenut my Hot to both X1/X2 wires and my Nuetral to wires labelled X3/X4.

Found a square D site showing 3 different ways to wire the secondaries. X1/X2 --- X3/X4 gave just 120. X1-- X2/X3----X4 gave 240 between X1 and X4, but you could also get 120 between X1 and X2/X3 and 120 between X2/X3 and X4.

A little confusing for the novice.

Here is a link that might be useful: Square D site

    Bookmark   January 2, 2012 at 2:14AM
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bus_driver

The implication in the initial post is that the supply (primary) voltage in this application is 480, one phase of a 480/277 WYE three phase, right? And the desired secondary voltage is 120, right?

    Bookmark   January 2, 2012 at 9:44AM
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brickeyee

This sounds a lot like a commercial application, and only licensed electricians are allowed to do commercial work.

    Bookmark   January 2, 2012 at 10:55AM
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Doug1984

Incoming power to my shop is 480/277 three phase, but I needed 120VAC single phase for a small control panel I added. So I took 2 of the 3 legs to supply the 480 to the little transformer (run through a fuse block to protect the transformer). I'm in the country and there are no inspectors or electricians other than me.

Thanks to Ronnatalie.

    Bookmark   January 2, 2012 at 12:06PM
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dkenny

don't forget a fuse/ circuit breaker on the output of the TX.

please measure the voltage before using just to make sure it what you want.

are you running the setup isolated? or grounded?

-dkenny

    Bookmark   January 3, 2012 at 8:25PM
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