I have a 2010 Ford Fiesta. Fuse 17 (Ignition Switch), keeps blowing every other week or so. This has happened 3 times and I would change the fuse. I have taken the car to 3 garages and the fault isn't showing on the diagnostics, as I have changed the fuse. 

How do I go about this? I've been told that once the fuse blows again, not to change the fuse, but to tow the care to the garage. This isn't practical for me. How can I make the fuse blow again, near by so that I can take the car in?

I really don't want to get rid of the car, but I have no idea what to do

Next time it happens, you could just fit a new fuse to get you home, and then swap the blown fuse back in afterwards...the garage would never know.

There is probably an electrical short somewhere which can allow the wiring to overheat and cause a fire.  This is why it's not recommended to just replace a blown fuse multiple times.  But as long as you're aware of that risk, that's what I'd do.

If it is only the ignition switch on that fuse then you'll probably need a new switch fitted unless the fault is detected with the wiring instead. 

Fitting a new fuse won't remove fault codes from the car though, I'd suggest trying a different garage if they're relying on fault codes to see why an ignition switch fuse is blowing...  

Also, without wanting to patronise, have you checked the fuses are definitely the right size?  Should be 15a iirc.