So I think I understand a bit more about why it's needed in some cases but not others. I'm going to describe what i think is going on, maybe you can help me clear up any points that I am missing.
The festool tools that they sell are not grounded, they only have two prongs in the plugs, this is fine in normal operation however when a large static charge is present it can overload a tool's circuits and fry something. Removing dust via vacuum generates static electricity, so festool solved the problem by providing a ground path through the extraction tube instead of via a physical electrical connection via the power cable.
So the danger is to the tool being used, not to the dust extractor. Therefore you can safely use a non-static hose while doing things like vacuuming the floor or using it on a tool that has 3 plugs instead of just 2 since it is already grounded. Therefore it should be safe using a 3rd party adaptor on a 3rd party tool since that tool didn't require the dust collection to be ground anyway.
Not totally sure if that's 100% right but that's what i've deduced from everything i've read on the internet. Thanks for all your replies by the way.
Some things I don't understand:
- Why was this done? It seems safer and easier to add a ground to the cord? I could see this being a cost savings thing, but other than that I don't imagine any other benifit to the end user of doing things this way.
- How do festool tools work with other non-festool dust extractors, or do they just not?
- Wouldn't the tools also generate static electricity without dust collection? This would mean using a track saw or sander without dust collection could fry the tool. Or is it just that the process of dust extraction provides much much greater amounts?
All-in-all it seems that festool provides very little information here other than just "don't do it" (i.e. don't use any hose other than anti-static). It would be nice if they provided some more specifics of the why, so we can be extra sure when we hit edge cases like this.