[ARC5] Need Help with Variac Diagnosis

[Bruce Long via ARC5]

For what it is worth I have a Chinese 2000 W 120vac variac purchased new three years ago on my workbench.  Turing it on and off i see no flickering on a 60 W incandescence light plugged into the same socket ( pair).
HOWEVER every 4 or 5 turn on's the relay in the UPS that protects my desk top computer clunks so I suppose that means there is a line voltage sag on some the variac turn on-s that is not enough to be visible on an incandescent light but is enough to trip the UPS
I don't think you should have enough in-rush current to trip your house breaker.  The fact you do makes me think whoever suggested to you that you have a shorted turn or two is probably correct.  

A shorted turn will act like a shorted secondary winding and alot of current will flow there.  That current should be present all the time the variac is powered on.  That additional static current could be enough to make the turn on surge enough to blow breakers.
Time to open it up and have a good visual inspection.


 
      From: DSP3 <jeepp at comcast.net>
 To: arc5 at mailman.qth.net 
 Sent: Thursday, February 19, 2015 7:53 PM
 Subject: Re: [ARC5] Need Help with Variac Diagnosis
   
Interesting, all.  I use a 220v/20A rated Variac adjust the nom. 120v 
line voltage going to a T-368.  I have never had a trip and it's on a 
15A breaker.    I am surprised by all this.  Perhaps the impedance of 
the 220v breaker is higher than a 115v unit?  Oh well.....  As an aside, 
I found that all voltages fall into "book value" by operating the T-368 
at 115v.

Jeep - K3HVG
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