I'm wiring in an electric hot water heater. I ran solid 10/2 in the wall. It has a black, white, and a bare wire. I brought the wire into the service disconnect. I attached black to "load" and white to "line." Then I use a AWG10 prefab 6' line to connect to the appliance. It is stranded. It has a black, red, and green. The appliance has a black, red, and green grounding screw. The two wires of the appliance are also stranded. In the service disconnect, I hooked up black to "load" and red to "line." Then with the appliance, I ran black to black and red to red with wire nuts. Then I attached the green to the green. When I energized the breaker, it tripped. I do not know exactly how the box is hooked up. Does it matter which is "load" or is there something else?

Yes, connect the black and white from the circuit panel to the line side and the black and red from the heater to the load side.

Hk:
"Yes" is ambiguous.

LINE is power in (wht/blk)
LOAD is the water heater (red/blk)

Thanks so much. That does answer my question.