Re: Power Load Balance Concern

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

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

In a message dated 9/23/01 12:13:38 PM Pacific Daylight Time, tesla-at-pupman-dot-com
writes: 


>
> Hi All! 
>        I am in the process of upgrading my power supply to 4 15/60 NSTs and 
> already have a 120v input -at-30Amp,  model W30M Variac. Based on nameplate 
> ratings, the NST bank  should draw about 33 Amps total (4X8.25). The problem:
>
> since there is only one open slot left in my breaker box, I would like to use
> a 
> 40Amp breaker, but I have not seen single breakers for this kind of current. 
> Most are dual breakers -at- 240 V using both sides of the line to keep the load 
> balanced and prevent in-house brown-outs.  If I try to get a 4KVA 
> step-down/isolation transformer so as to utilize both sides of the line, I am
>
> looking at ~$350 plus S&H on 120 lbs. 
> Questions: 
> 1. Is running the Variac at +10% a real concern? 
> 2. Is placing this size load on one side of the panel going to create
> in-house 
> imbalance problems? 
> 3. Anyone got a cheap step-down 4KVA transformer? 
>
> Would appreciate response from any/all with experience in this area. 
>
> Matt D. 
> G3-1185 



Matt, 

Running 10 or 20% over rated power on the variac should be no problem.  I do it
all the time.  I usually run on for a few minutes then off for a few minutes. 
Try it and see how hot it gets.  You don't say how large your braker box is. 
If it is a 200 amp service, there should be no problem - again, it is not like
you will be running 40 amps continuous duty.  You might look at getting a 240
volt variac and running two of the primaries in series with the other two
transformer primaries in parallel with them.  You might also try power factor
correction caps across the primaries to reduce the required current. 

Ed Sonderman