Wow, I had no idea what I started. Great thread and I have learned a lot.
The last discussion about cautions on oversizing wire has me scratching my head though. I have reviewed both Nigel Calder's and Don Casey's books and all I find there is to make sure the wire is big enough for the anticipated load. I don't see anything that says to make sure the wire is not too big. In fact I think both say oversizing is good.
For my rewire project the tables say for a 5 amp draw with a 40 foot round trip run 10awg is the wire to use. For my run of lights through the boat on either side this is what I need and will be my longest run. I was going to use this gauge for much of my wiring and then a smaller gauge say 14awg for the running lights which are a long run but will only have a 1 or 2 amp draw.
I don't see anything that says don't use wire that is too big? I know I am probably paying a little more than I need to but felt it easier to just have two spools of wire and pick the one that is larger than needed for each run.
You will regret the things you did not do, more than the things you did.
Get out there!
Saco Bay, Maine
2001 Beneteau Oceanis 361