Hello, I am installing a 100 amp sub-panel in my 48x30 morton building. I have only installed and buried 1" schedule 40 pvc from the house. I was planning on installing #4 thhn wire to supply this until I read in the code book that #4 can only be used for the main feeder panel, so now I have to go up to #3 wire. I am also using #8 wire for the ground to a grounding rod. Three #3 wires will fit in the conduit and to code, but it will be hard to pull. My question is can you down size the size of the neutral, or does it have to be the same size?