Re: Grounding pigs

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 2/15/02 10:31:19 AM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:

<< Hi David - 
 
 Why "must" you remove the strap? There is still 240 across the 2 internal low
 voltage windings even with ground at the center tap. Same voltage across, 
same
 inductance across, same current, same output. In the event that the 2 low
 voltage windings are paralleled, then you have a condition where you would 
only
 allow 120v from the center tap to one of the end windings. But even in this
 case, neutral would go to the center tap and could be tied to ground. In 
either
 case, I don't see why the strap "must" be removed. Maybe I'm missing 
something?
 
 
 Take care, 
 Bart 
  >>

Hi Bart,

True, if the strap is left connected you will have +120 volts to one outer
LV bushing and -120 volts to the other, relative to the grounded "strap"
on the center terminal. It will effectively be two 120 volt sources, out of 
phase (or is that in phase) Let's don't get started on the "phase" thread
again :-) But most pig coilers are going to opt to power their pig trannies
through a 0 - 240/280 volt variac and here is where the problem would ex-
ist by leaving the strap connected. A 240 volt variac basically has infinite
range of output voltage between 0- and 240 or 280 volts. So that is what
you want to feed into your pig. If the center strap is grounded, that will
shunt the inputs from each leg of the variac to ground. "I" personally see
that as a problem.  And if you don't  "ground" the strap, then you would 
have the entire external tank of the pig floating at 120 volts in reference to
ground :-(  Maybe I'm wrong here, I certainly have been before :-) Maybe
it would still work if you left the LV bushing grounded to the case (and
made sure that the case and the strap were actually connected to ground)
but leaving the center LV bushing floating has certainly worked for me
without any problems and I'm not going to try changing it (if it works,
DON'T fix it) ;-) Maybe others have comments on this?

Coili' in Memphis,
David Rieben