Hi, I need to hard wire a 240 volt 5000 watt heater. The heater has two black wires and one green ground wire, one labeled L1. I know both black heater wires are hot and to be connected to the two hot wires from the 10 ga 2 wire. Does it matter which 10 ga hot wire goes to the L1 wire on the heater?

Also, how exactly do I connect together the ground from the 10 ga wire to the ground from the heater? Do I connect both grounds together via a wire nut or do I connect both grounds to the same point right on the heater chassis? The back of the heater has a junction cover where the wires are and the cover has two punch out holes for wire bushings I suspect. Is there a bushing of some sort I can install in the second hole that will properly couple the two grounds? I don't see a screw on the chassis specifically for the grounds.

My main panel box has a common neutral/ground bus (white and grounds are in each bus on both sides), which will receive the ground wire from the incoming 10 ga. The other two hot wires will connect into the double pole circuit. I'm mentioning this also just in case I have this wrong.

Thanks in advance.

For two 240 volt conductors, does not matter which terminal they are connected to , as long as the two terminals are for a 240 volt input.

Ground wires an be connected in any fashion, with terminals, pigtail, or wirenuts, as long as all grounds are connected and the frame is connected.