Variac blowing fuses (another newbie questin)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: otmaskin5@xxxxxxx 

Thx for all the responses.  Several of you asked for more info in 
order to diagnose.  Here's the info.
- The variac is supplying power to the NST only

- Original fuse was 20A - don't know whether it was fast or slow 
blow.  Replacement fuse was 15A SLOW BLOW.  When it blew, the solder 
breached the fuse's glass cylinder.
- The fuse blows after I've dialed the variac up to full power from 
zero. It didn't blow immediately - rather, the coil ran for maybe 
10-20 seconds.  I believe the variac was up to full power.  Both 
times, the fuse blew during strong continuous arc to grounded 
target.  Hasn't happened when streamers were not striking 
anything.  I always power up starting the variac at zero.
- The variac provides 0-130 volts out.  Current rating is 20 amp.

- Fuse appears to be located in the input circuit of the variac (not 
totally sure as I wasn't able to get the cover off far enough to 
thoroughly examine the wiring).
- I don't know whether the NST is a high power factor type or a 
normal.  I'll check with the
mfg to see if I can find out.  In the mean time, it's a Franceformer, 
15000 volt, 60 ma, 890 VA, model # 15060.
- My tesla coil has a static spark gap.  9 gaps made of 3/4" copper 
pipe 0.03" for each gap.  So far, its wired to use only 4 gaps (0.12" 
total) and small fan for quenching.
- The value of my tank capacitor is 0.03 uF +10%, 35KV.  I'ts the 
Maxwell cap you see on eBay quite often.
- The variac works (as indicated by the voltmeter) without blowing 
fuses @ no load.  Also, I run my small coil (9/30 NST powered) using 
the variac haven't blown fuses.
Hope this helps in figuring it out.  Thanks.