I am in the process of building and will soon be wiring a detached 20' x 12' shed in my yard. The run from the service at the house to the sub-panel in the shed will be a total of 47 feet(including the vertical portions of the run), so, I'm using 50 feet as a basis. I intend to have the smallest electric water heater that I can find. 5 to 10 gallons if possible, and a welding machine that pulls 20 amps. I have decided to run 8/3 with a ground buried in PVC fed by a 30 amp circuit breaker. I have done considerable reading on the subject, and I have been confused by some things that I read. All of the switch boxes that I use will be plastic. So, according to what I've read, I don't need a continuous grounding wire. However,some things that I have read imply that I will need a dedicated outlet for the water heater with a continuous ground. ( The water heater will not be continuous use. Perhaps one to two days per month. The rest of the time, the breaker or switch feeding it will be off). Also, I have read that sub-panels don't require a main breaker (or disconnect) upstream of the branch circuits. If I read correctly, the feed will run as follows : the double pole 30 amp breaker (for 220) at the service panel, 8/3 with a ground to the sub-panel bus bars, and the neutral bar , and then on to the branch circuit breakers. (I would prefer to have a main disconnect at the shed). The first receptacle of the two branches containing receptacles will be GFCI protected. The neutral and ground bars of the sub-panel should not be bonded so, where will the continuous ground flow to? Two final questions, does the sub-panel need its own ground from the panel frame to an electrode, or does the ground wire connection to the service panel suffice, and what size PVC do I need to run the 8/3 with a ground ? Thanks