Is the big lead going to the alternator supposed to have juice even with the key off?

So I'm taking Dons' advice and running a lead from the STA on the alternator to my choke to see if that will fix my tach (I had been using a lead from the "+" on the coil). When I disconnected the big wire saying "BAT" on the alternator it accidentally hit the body and sparked just like if you hit the battery positive lead to ground. I would think the key would need to be on for that to happen. The car has always seemed to run fine and charge properly. Is that normal? Thanks.

Yes, that line is connected to the battery side of the starter solenoid, which is also connected to the positive side of the battery. 

You should always disconnect the battery when doing electrical work, such as connecting/disconnecting lines.

Thanks Randy. You are so right. I had a momentary lapse in judgement.