I read the following statement on another site.....
"Good grounding of dust collection ducting is essential to reduce the risk of static discharge, which can cause a dust explosion under some conditions."
Is this a real concern?? The guy who did this grounded the wire inside the flexible tubing so as to take care of it, but this to me seems like it wouldn't help a lot since the wire itself is encased in plastic and never actually in contact with the static charge build up. Then, later the same guy made a new system from PVC piping, 4" diameter stuff, and drilled a series of holes every 4" along the pipe, put a screw in them, and strung a new wire from screw to screw wrapped in a spiral around the whole thing to repeat what had been done in the first set up.
I'm planning to run 4" PVC around my shop for dust collection, but I didn't know this much detail was necessary to pipe dusty air into a containment unit.