Re: 240 vac variac observation

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>


> 240 volts to common??? Where did that come from?

	It is found in industrial applications, hence some Variacs
	are wound for that voltage.

	Also, if intended for export, where 240/480 is used much
	as the US used 120/240.  That Said, however:

> We're obviously having a communication breakdown.

	I believe the 240 v variac is being used on normal
	residential 120/240v US circuit.  I would never use it so,
	unless a good, tested, monitored, isolation transformer
	is also used, either at input or output. 

> Adam Minchey, P.E. (credentials)
 
> --- Tesla list <tesla-at-pupman-dot-com> wrote:

> > In house wiring in the US there should NEVER be 240
> > volts AC to common.  I think you are using the two
>>hot wires to feed your variac.

	Concur.

>> Your drawing is not correct.

	Drawing is ok, BUT use of term 'common' as used
	therein is highly unusual.  (one might say 'wrong'.)
	By deep convention, common is applied top the 'neutral'.
	In verbal/textual communication, redefining the terms is
	iffy.
 
> > If you do have 240 AC to common/neutral then you
> > have a dangerous condition and it should be corrected
> > immediately.
> >  allan

> > ----- Original Message -----
> > From: "Tesla list" <tesla-at-pupman-dot-com>

> > > Original poster: "Yurtle Turtle by way of Terry
> > Fritz
> > <twftesla-at-qwest-dot-net>" <yurtle_t-at-yahoo.

> > > You're missing my point. With two 120 volt variacs
> > > back to back, there are TWO brushes. My 240 volt
> >> one has ONE.

	and is designed for use in a 240/480V system, rather than
	a 120/240 v one.

> > > I never stated anything about PHASING, I simply
>> > stated that varying my 240 volt variac results in an
> >> output of 0 to 240 volts, RELATIVE TO THE COMMON.

	This usage of the word 'common' almost guarantees
	miscommunication.  by Deep convention, that line
	is called line 2, or the other hot or whatever.

>>> And in residential 240 volts usage, WITH MY VARIAC, the
> > > common is one leg (excuse me for using the word
> > > phase).

	This is a most unusual use of the word common.
 
>>> This results in one output leg at a different
> > > potential RELATIVE TO THE NEUTRAL than the other.

	It will.  Risky.

> >> You don't need a scope to prove this, just look at my
> >> ugly ascii diagram below and noodle it out. At any
> >> setting, I get 120 volts differential between the common

	This is a most unusual use of....

>> > and the ground. This MUST BE, if you look at how the
> >> thing is wired up.

	I'd not use it that way.

>>> I also confirmed this my my DMM.  How else
> > > could this thing be wired?

	On a 240/480 v circuit, which is what it is designed
	for.

>>> Of course, this doesn't matter when I use my pig, as I don't
>>>use the house neutral/ground connection.

> > >  --------)
> > >          )
> > >          )<------  0 - 240 vac
> > >          )
> > >  240 vac )
> > >          )
> > >          )
> > >          )
> > >  --------)--------  common
				A most unusual use of the word common.
> > >  ------------------ neutral/ground

	best
	dwp