Re: How are 240 VAC variacs made?

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Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 


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From: "Tesla list" <tesla-at-pupman-dot-com>
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Sent: Sunday, February 29, 2004 2:57 PM
Subject: Re: How are 240 VAC variacs made?


 > Original poster: "Hydrogen18" <hydrogen18-at-hydrogen18-dot-com>
 >
 > you completely missed the point....are they center tapped to ground or
not?
 > Obviously 2x 120 vac's ganged together are or can be, but are the single
 > core 240 VAC ones center tapped?

No, they are not.. You might be hooking it across a delta connected 240 V
supply, and so, both wires are "hot".  That said, I will say that I have
seen variacs with a center tap on the winding, but they still have only one
wiper.  What you're really asking is if 240V variacs have a pair of wipers,
so you can feed 120-0-120 in and get x-0-x out?
You can do this if you're ganging multiple variacs together.


In a three phase variac, they are usually connected in Wye (star), with the
low ends of the variacs tied together, even if the supply is delta fed. If
you hook three variacs in delta, all moving the wiper(s) does is change the
relative phase between the input and output, but the voltage remains the
same. (draw a little picture/schematic, and this is obvious... three wires
in and three wires out)