> I don't understand how the grounding cable can remove more than
> just the charge immediately surrounding it, as plastic is non-conductive.
> For example, isn't it the same as putting a grounded wire across your
> TV screen? Only the charge within the immediate vicinity of the wire
> will be removed, but the rest of the screen will be unaffected. Unless
> the piping is lined with a fine wire mesh, how can it work?

If I remember my physics, on a non conductor the charge spreads evenly along the surface, distributing itself according to the geometry of the structure. Dust moving through that pipe could wipe off electrons, creating a charge on the surface, and an opposite charge on the dust particle, much like rubbing a piece of plastic with a cloth. With a bare wire in the tube, the moving dust might strike it, transfering the charge to the wire, which carries it off. The longer the tube, and the thicker the wire the better your odds here. A mesh might be better, but if a single wire works, then go with the simpler method.

However, I suspect the wire is there to ground something at the far end of the tube, so that there are no sparks at that end, as opposed to inside the tube where the charge is rather weak, and already spread over a pretty large area. By the way, for the vast majority of home wood shops this is not a problem. Assumoing average humidity, most people would have breathing difficulties long before the sawdust got to an explosive level. Keep the shop clean. In dry, enclosed conditions: Keep the shop cleaner. Paul Jacobson