To care or not to care?


Eric.

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​For me, it was about the occasional shock (which in the winter and coming-off a wide-belt sander can be rather painful) and not having dust sticking on the flex hose connections. I use metal ductwork, fittings, blast gates, etc... so, for me, it was a quick/simple effort. I only had to jump one plastic inlet, so it wasn't a big deal... Now, if you've got an all-PVC setup, then it's more of an effort -- but still, a 500' spool of braided 24g copper ground wire is maybe $10... http://www.mcmaster.com/#catalog/120/3782/=rktc4r

 

 

(Theoretically) couldn't I just expose some of the metal ribbing on my hose where it meets the PVC, slap a hose clamp on it so it's solidly in contact with the PVC, and have that conduct the static away from the pipe?  Or is the static diffused all over the pipe to where even if one end was grounded you could still get shocked at the other end?

 

I don't have filters. :)

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Normal sawdust may not be fine enough to hang in the air in appropriate densities to create a spark-ignited fuel/air bomb, but I bet MDF would!

I can't say I've ever heard of a cabinet shop exploding this way, but it is not uncommon in graineries. Heck, even steel mills like the one where I work sometimes creat conditions that produce these kinds of explosions. Even iron / steel dust, if fine enough, will burn.

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==>(Theoretically) couldn't I just expose some of the metal ribbing on my hose where it meets the PVC, slap a hose clamp on it so it's solidly in contact with the PVC, and have that conduct the static away from the pipe?  Or is the static diffused all over the pipe to where even if one end was grounded you could still get shocked at the other end?

 

The short answer is no....  The short reason is that PVC is an insulator and inhibits free field/charge flow -- i.e. the charge builds up [mostly] evenly along the entire pipe and your body becomes a convenient path to ground (hence the shock). Attaching a single ground wire to the PVC at one end of the pipe doesn't do anything for the charge at the other end --- actually, it does something, just not enough to influence the potential for a shock... In other words, your body remains the better path to ground. This is really an over-simplified explanation and a bit wrong, but the proper explanation gets rather esoteric and too long for posting late at night... I'll write-up a couple of paragraphs tomorrow...

 

To provide a quick/dirty answer (until I get around to a proper write-up)... You can deal with charge build-up with an inner ground path (typically copper grounding braid) to accelerate charge bleed-off and/or an outer path to ground (also typically copper grounding braid) to provide a path to ground that's favorable compared to your body. Luckily, copper grounding braid is really cheap --- about a thousand feet for $20. Now before the EEs in our studio audience jump in and point-out that this approach doesn't really solve the problem, it does have the rather singular advantage of actually working in the real world... You still have charge, but you've also created have a favorable path to earth compared to your body. Just a reminder -- you don't really ground the PVC ductwork (it's not actually possible), you're just providing a favorable path to earth. There is no explosion hazard and not even much of a shock hazard for most stationary tools. Folks tend to start considering ground wires when they get a drum sander or decent-sized planer... Until then, the shocks are rather minor -- annoying, but still minor (as long as you're not spraying solvent lacquer in the vicinity)... But if you ever get a wide-belt, dual-drum sander, et al you can build-up an impressive charge that should be addressed -- these shocks are not so pleasant... But in reality, the situation normally never arises -- folks who sped $10K+ on a sander, usually don't try to save $500 by running PVC...

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