Re: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?

The potential danger in using a variac is that one side of the output is
connected directly to the power source and, if you turn it all the way up,
both sides are. So it becomes as dangerous as, say, a wire plugged into the
wall socket. 110v residential power is typically one leg of a three-phase
line from a Y-connected three-phase transformer. Generally the common leg of
the three-phase line is in fact connected to earth ground, so one side of
your 110v line is at ground potential. This is where we get the
hot-wire/ground-wire terminology. So if you connect the common side of your
variac to the ground side of the 110v line, and use the variac to reduce the
line voltage, and bear these facts in mind, it is in fact no more dangerous
than an isolated transformer. On the other hand if you don't know what
you're doing it probably is more dangerous than an isolated transformer. But
in that case, working with high voltage is dangerous no matter what you do.
I suspect that the argument arises from the tendency for people who don't
know what they're doing to assume everyone doesn't know what they're doing,
and that to be safe we all should live with the same restrictions as the
least competent. Another name for that reasoning is socialism, but that
would be OT (wink wink nudge nudge.)

So the moral of the story is, if you know what you're doing, you can be as
safe as you choose to be.

--Phil M.

----- Original Message -----
From: "Andy Wander" <awander@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, January 13, 2012 7:24 PM
Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?


> Hi Mike:
>
> I had a big argument/discussion about this very subject on one of these
> message boards a few years back. It was basically me against everyone
> else(who cared to comment).
>
> The gist of the explanation that I got was, "There's no galvanic
> isolation", and "If you can't see that it's dangerous, I'm not going to
> bother telling you why". People got very upset and angry at me, but nobody
> seemed to be able to explain the danger.
>
> I have since looked at it a lot more, and I believe that the danger exists
> because even a big transformer, if it has isolated windings, will tend to
> limit the current that can flow through it, and so the case where there is
> a direct connection to the power line "could" be more dangerous. But I
> have still not seen a good, easily understood explanation.
>
>
>
> Andy Wander
>
> -----Original Message-----
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of mikep_95133
> Sent: Friday, January 13, 2012 9:02 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?
>
> Understood. So why do I need the power supply isolated? Everything in the
> shop is grounded. The floor is concrete.
>
> When I first set this variac up, I took a voltmeter and probed from the
> mill to everything within 6 feet and there was no voltage delta.
>
> Mike
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "picengraver" <picengrave@...>
> wrote:
>>
>> Mike,
>> A Variac's output is NOT isolated from it's input as standard
>> transformers are. The risk of electrocution is high if one comes into
>> contact with the output voltage and earth ground (floor, water piping,
>> machine frame, etc.) Why risk someone's life?
>>
>> Regards,
>> John Champlain
>> www.picengrave.com
>>
>> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "mikep_95133" <mikep_95133@>
>> wrote:
>> >
>> > Really? How so? It's only been a part of the system for years now.
>> >
>> > Mike
>> >
>> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Dan Mauch" <dmauch@> wrote:
>> > >
>> > > Using a variac isn't safe. You really shouldn't use one with your
>> > > servo
>> > > system.
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > Dan Mauch
>> > >
>> > > www.camtronics-cnc.com
>> > >
>> > > dmauch@
>> > >
>> > > Stepper and servo motors
>> > >
>> > > Kits, assembled and custom CNC using Gecko products.
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > [Non-text portions of this message have been removed]
>> > >
>> >
>>
>
>
>
>
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>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it
> if you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are there, for
> OT subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
> Yahoo! Groups Links
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>