strange variac

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Original poster: "Andrew Genseal" <aggniu-at-hotmail-dot-com> 

Hello all,

This is my first time attempting to post anything, so please bare with 
me.  At any rate, I am in the process of building my first coil and at a 
recent Ham-fest, I picked up a variac that looked as though it was in 
excellent shape (good brush, easy rotation, no burnt windings).  Anyways, I 
have come to find out that I cannot find any litterature anywhere about the 
terminal assignments for this thing(except for the brush on T-3).  It is a 
Staco Adjust-a-Volt with the following characteristics:
Type: 500 BU
Rated Current:  7.5A
Input V: 120V 50/60Hz
Output V: 0-140V
Additionally, it has 7 terminals to choose from(That is the real source for 
my confusion).

The first time I hooked it up with the common on T-4 and hot on T-5, I got 
140V at max scale between common and brush.
The second time, I used T-4 for common and T-6 for hot and tripped the 
circuit breaker.
Then, I changed it back to T-4 and T-5 and was checking the current into it 
with my meter in series.  It was not drawing much current in a steady state 
senario, but once I hit the terminal and backed of and hit it again and a 
nice spark roasted my fine point of my meter into a flat.  Is this the 
effect of "inrush current?" (BTW, it was still operating at the prescribed 
140V out at max on the scale.)
Also, if anybody knows anything about this crazy variac.  How do I hook it 
up to get 120V max output for my NST?
I cannot find anything from Staco's site that says that this thing ever 
existed, so any help will be greatly appreciated.

Thanks,
Andy