I have a shed about 300 feet from my house. There is a circuit breaker box with two 20 amp breakers. Each breaker feeds a single 20amp outlet. Each breaker is connected to a #6 stranded wire that go back to a 30 amp breaker in the main panel. There is not a neutral or ground going back to the main panel.
In the box in the shed, the outlet ground and neutral go back to a neutral bus that is bonded to the ground bus. A single #6 solid copper ground wire connects to two eight foot long ground rods (the rods are about 8 inches apart if that matters). This setup was installed by a previous owner and has worked for years to power a light and some tools, and sometimes a space heater. Recently, a friend said I had to run a #6 neutral wire back to the main panel, but could not tell me why it had to be done. I looked in the main panel, and all the neutrals and grounds go to the same buss. This new wire would be pretty expensive and I don't want to do add it if it is not necessary.