I cut through the 220 volt line to my dryer, and spliced in a short piece. The older wire was aluminum, and each of the three wires had black insullation--no way of knowing which was meant to be red or black or white. When I turned the breaker on, it sparked and immediately snapped off. The cut is far from either end. Is there a way to tell which of the wires should be spliced to the other, since all are black?

If you look close, you should see a red tracer on one wire, and a white tracer on another, leaving one wire completely black.

If this is the type of cable I think, the tracers are hard to see , but they are there.

If so, then splice color for color.

Otherwise, you will need a ohm meter or continuity tester to ring out the wires to figure out which is which.