First let me tell what I got and say I hope to get some help.I will appreciate anything.I was given a spa.My brother and sister in law said it was a good one but wont fit the renovation plans. It is an A.S.I. brand spa.He told me he couldnt find the breakers that were in there. He wasnt sure what happened to them. What I found in the on board electrical box was that the black and red legs from the unit that would normally go to the breakers were hooked in the pegs that the incoming supply legs should go.The screws were loose as if to remove the incoming wires.I deducted that they skipped the (missing )breakers and just depended on the house hold breakers at the main box.Is this wise? I have to run about 40 to 50 feet of wire from my main box,go under my house to the spa.Can I use some outdoor 10/3 or do I have to use the 8/3 outdoor?This will be connected to a double pole 50 amp at the main.The unit has a weathered sticker type label that is hard to read.It says it is a 220 unit that is not convertable to 110.It says that is a 50 amp 6 kw unit.Some one took an ink pen and drew a 3 over the 5 changing it to 30 amp.I want to use the on board box. 30 or 50 ?

You should go to some spa manufacturers sites ( like http://www.laspas.com/Install.htm ) to get generic wiring information. I used #6 (4 THHN in conduit). The way I understand it you need a disconnect (which is usually the GFCI breaker) visible from the spa and no less than 5 feet from the spa and no more than 50 feet.
The spa pretty much counts on the GFCI to trip if the heater shorts to ground. Home Depot sells GFCI breakers in a box for spa use and just about everything you would need to connect it. Wiring to the spa is a serious safety issue and if you have any doubts after reading the information available on-line, I would recommend having a licensed electrician who has wired spas check your wiring before applying power.