Re: Autopsy - Post Mortem of a Variac

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 3/9/01 8:25:34 PM Pacific Standard Time, tesla-at-pupman-dot-com 
writes:

<< Hi All...
 
 back again with the info on the Variacs that got fried Via the hi Volt surge
 from the safety gap.  Yes the safety gap fried the 240V system ( I found a 
spot
 on the rim of the cap of the pig where the RF ground wire from the center 
ball
 was too close, the paint was burned) plus, I'm going to ground the pig case 
to
 a dedicated ground!!!!!!
 
 anyway ....  what i found was that the arc point occured between the variac
 form/windings and the "so callled insulator" that holds the form/windings
 secure from the mounting bolts of the variac frame. What could be considered
 here is that the hi volt surge made its way thru the windings and broke the
 insulative covering on the support and from there the normal supply voltage
 took over from there and fried the first 5 wraps of wire on the core.
 
 there is alot of "spatter" from the melted wire and a good deal of grey soot 
on
 the affected variac ( well at least this is good, only one variac got bit )
 just a matter of rewiring 5 wraps....
 
 BTW    the variacs are 1256D models 240Vin 280Vout  28A units....
 
 soooooo...  if any of yall have these types of variacs...  consider breaking
 them down and adding some additional insulation between the mounts and the 
core
 ( im going to use some polyuerathane rubber 3/32" thick)
 
 be back later .......
 
 
 Scot D >>

Scot,

Sorry to hear about your variac.  I use a separate ground rod for my 60 hz 
circuitry which includes the case of the 5 kva transformer, cases of the 
variacs and the line filter ground.

Ed Sonderman