Re: Pig questions

           Re: Pig questions
           Sun, 06 Apr 1997 13:05:10 -0400
           "Edward J. Wingate" <ewing7-at-frontiernet-dot-net>
           Tesla List <tesla-at-pupman-dot-com>

Tesla List wrote:
> Subject:
>         Re: Pig questions
>   Date:
>         Fri, 4 Apr 1997 13:14:40 -0700 (MST)
>   From:
>         Chip Atkinson <chip-at-xig-dot-com>
>     To:
>         Tesla List <tesla-at-pupman-dot-com>
> Greetings,
> As a fellow pig handler, I thought I'd add my experiences.
> As has been stated, the arc welder is put in series with the pole pig.
> This means that one side of the power line goes into the welder, then
> out
> of the welder, and finally into the pig.
> The most important bit of experience that I have is when connecting the
> variacs, welder, and pig all together.  I originally had the welder
> between the pig and variac, but since I also had the center tap of the
> pole pig connected to the house neutral (center tap of the neighborhood
> supply transofrmer), the breakers would trip even when the variac was
> turned down all the way.  Here's why:
> 1-------------- W -----------
>        3\         CT  ______ 3
>      V 3 \           /       3 PP
>        3  \________ /________3
> 2------            /
> ------------------/
> W -- Welder
> V -- Variac
> 3 -- Windings of a transformer
> PP -- Pole Pig
> CT -- Center Tap (Neutral)
> Note that the \'s which represent the movable part of the variac
> effectively short out the ends of the pole pig.  The problem arises
> when the current comes in on line 1, bypasses the welder W, and goes
> between the CT and the hot line 1.
> I am now rewiring my power cabinet to place the welder before the
> variac on the common line of the variac.  This will allow me to
> connect the center tap of the PP.  This is not electrically
> important to my knowledge, but I just don't like the idea that I
> can't connect a wire up that's not supposed to have any effect and
> cause a short.  I also have to re-meter the thing anyway since my
> voltmeter basically blew up, and my ammeter is not working
> correctly, and I want to put in a variac for the rotary gap, and I
> like tinkering with this stuff... whew.
> Oh, BTW, I took the volt meter off the panel it was mounted to and
> found that it had blown a pin hole through the 16ga steel that it
> was mounted on.
> Chip

Hi Chip,

It is not a good idea to connect the center tap of the low voltage side
of a pole transformer to the power company neutral or ground. I really
don't understand what the reason for doing so would be. It is, however,
a MUST to ground the case to avoid serious problems in case of a failure
or malfunction so the high voltage can't find it's way back to the
operator through the floor (concrete or even supposedly dry wood are
better conductors than you might think) or the primary wiring. The
center tap and case on a pole transformer are not electrically connected
internally. There is usually a built in spark gap prong protruding from
the bottom of the center tap/neutral connection and pointing in toward
the case for lightning protection, but they are not connected. The only
reason I can think of to use the center tap would be to run the
transformer on 120 volts. Otherwise it should remain unconnected.

Happy and Safe Coiling,

Ed Wingate