Wiring garage assistance...please? I am wiring a garage and I requirement 100ft of wire to...

I am wiring a garage and I requirement 100ft of wire to run from my house panel box(200amp) to 100 amp garage panel box.
My problem: I own two lengths of #3 calculate wire(3/3 copper wire) one is 60ft and one is 40ft. Can i put in a intersection box and splice them together or is it against code?
Seeing this as a fair sized telecommunication and marrets cannot be used, what can I use?
Answers:    yes , code requires a splice to be in a box,
capture copper wire lugs at a hardware or elect outlet, a roll of insulating cassette, and a roll of elect tape, wrap the lugs beside insulating tape 4 to 8 turns, next wrap the elect tape 4 to 8 turns around. cover it completely, close box beside a screw
I am just guessing here But I would right to be heard that that is a concrete no-no as far as code goes and it go against common sense to.That anyone said I'll say this.I would do it provided you don't intend to be drawing any really serious amps thru this flash I.E. welding or some such item and where you connect the wires together solder them and after wrap ALOT of tape around them....Good luck