I have a new Image\Weslo spa. It calls for a 30 amp service. I have a brand new home and 200amp GE Load center. I have the nice GE GFI 30 amp breaker in the main box. Then i plan to go 40 feet to an external disconnect. Put in a switch (planning on a basic disconnect) and then go 15 feet underground to the tub. My concern is I put in 10\3 on the run to the external disconnect, i have not bought wire for the rest. Should I go with it or replace the 40' 10\3 run with 8 or 6 ? or shooould I just use it and put 8 or 6 from the disconnect to the spa. Or just keep the whole thing 10\3?

because portions of my house are unfinished it would not be all that hard to replace the long 10\3 run, by the way, but I am poor now after building a house, and dont want to overkill it. The reason why is that documentation for the spa shows an example with 8 gauge. I believe all my wire is copper.

thanks

Jeff

Here is handy wire size caculator, full run determines wire size, keep that in mind.

Run 8/3 for that length and you'll be ok.