I would use a crimp-on style terminal like you see on the starter end of a cars starter cable then bolt the 3 terminals together and insulate with high voltage tape.
Ok I went to Tracpipes website and found out I would have to use their product that has a black covering for direct burial and I found out what 7" WC means but when I tried to use their sizing chart I was lost.
Thanks for the responses I have gotten answers anywhere from 3/4"
to 1 1/2" from HVAC guys I just don't want to have problems after the supply line is buried. I was planning on using the yellow flexible stuff you can get at Menards I dont know the technical name for it. What is Trac pipe, Ward...