Underground feeder in conduit -- allowing slack?
I am about to install a new subpanel in a detached garage, about 100 feet from the main panel. There is 2 inch pvc conduit in place. It is about 3 feet underground, with risers at the house and garage. (FYI, it contains 2 45-degree bends, plus the 90's for the risers before entering the buildings via conduit body fittings.) I will be installing an aluminum feeder of 3 1 Ga cables plus ground.
Now, my question is, do I allow slack for thermal expansion and contraction of the aluminum wire through the different seasons? (This is Wisconsin, the conduit is not below the frost line, plus there's the outside portion of risers at each end.) If so, how much slack is required, and how is this accomplished, given that I'll be pulling through a conduit, not burying the cable directly in the ground? Some slack can be left in the main and subpanels, of course, but is that enough?