This might sound a bit counter intuitive, but stay with me for a bit. I am designing my dust collection ductwork system and have come upon the following question while considering the "all metal" option.

If we accept, for a moment, that grounding for static charge within any duct system (plastic or metal) is important and that using metal is generally seen as preferable to plastic as plastic is an insulator, wouldn't it be necessary to ensure that the metal pipe grounding circuit is complete through to the ground for the main electrical circuit?

If I understand this correctly, most metal pipe systems "terminate" into a plastic flex pipe that is often fixed to a plastic hood that either comes with the tool or is added by the owner. Unless the metal pipe has some form of conductive connection to and through the flex pipe as well as the plastic hood through to the machine and eventually to the electrical system main ground, I am thinking that the static charge ground system is not complete.

I have read two different "guides" for designing systems and neither mentions completing the static charge circuit to the metal frame of the woodworking machine. Am I missing something here? Do most folks make these connections even though at least some of the guidance out there is silent on the subject?

I am aware of the argument that one main benefit of metal pipe is that static charge is less likely to build in the first place, however less likely is not the same as "will not" and most metal pipe systems seem to have plastic flex pipe to the machine which is apparently thought to be more likely to contribute to static charge buildup. For the purposes of this question, I am assuming that part of the benefit of the metal pipe is to allow for grounding of whatever static charge builds up in the pipe as a result of fine particles colliding with each other and that for grounding to really occur, one must complete the circuit through the metal frame of the machine.

Any thoughts on this?

...Bob