A home owner called me out to resolve a dispute he is having with a home warranty company over his spa. The spa is leaking and the company subed out to fix it won't touch it because it is wired to the disconnect with Alumunum wire. It is a 50 Amp 240 Volt sub-panel with a GFCI breaker. The wire size looks to be #8 which I believe is too small. But that isn't the issue the company is raising. They are saying the alumunum ground wire is not to code. I might add that from the sub-panel to the spa itself, it is wired with #8 copper and #10 copper for ground. All connections in sub-panel use anti-oxident. Does anyone have any insight into this, or can point me to the right place in the NEC where I can find the answer?

Many thanks,
Byron Wise

Many spa instructions specifically say to use #6cu, even though this is overkill for 50 amps. #8 al is undersized for 50 amps but this should have no bearing on the spa. The manufacturer has no say in what you feed a panel with and is looking for a scapegoat. The fact that they think something is not to code is no reason to void a warranty due to a leak. If it were an electrical problem I can see them causing a stink.
I can't refrence the exact article but it's right in 680. Within the structure conventional wiring methods can be used. Romex and aluminum wire included. Once you exit the structure the pool/spa codes become stringent.

We run 8/3 for spa feeds unless #6 is specified. Then 4-#8's (or #6's) in sealtite to the spa itself from the disconnect.