I am setting up a new workshop and the plan is to have as dust free an environment as possible. Very few articles I have read about workshop dust collection mention grounding the plastic elements of the system but Lee Valley (from whiom I obtained much of the necessary bits and bobs) is adamant in the instructions that come along with the plastic components that they be grounded to avoid the risk of static build-up and sparking in the system.
I do believe this is a real problem from an experience in my old shop. There, I got a new DeWalt 13″ planer and attached a dust collection hose with a cyclone type plastic garbage bin top and a shopvac. The first time I used it I noticed a 1″ long spark arcing between the dust collection hose and the planer table. Promptly turned it off and installed a grounding wire.
In the new shop the main dust collection trunk line is 5″ 26 gauge galvanized duct, but the branches leading to the machines are mostly 4″ PVC tubing. I carefully fed bare copper wire (supplied by Lee Valley for this purpose) through each of the plastic ducts and attached it to metal at either end with eyes and screws. No matter how taught you make the grounding wire, when the suction turns on, the flex tubing contracts a bit, leaving the wire a bit slack. In this state it collects a lovely big, bushy raccon tale of planer shavings which in short order obstructs flow enough to create a blockage. See photo. The shavings get trapped between the strands of loosely twisted wire. To be honest this is mostly only a problem with planer shavings (rather than sawdust) and I have had to remove the grounding wires from the planer dust collection lines. The planer is still grounded to the galvanized duct, just there is no longer a wire running inside the tubing between planer and galvanized ductwork. I am working on the assumption that static electricity builds up over distance in a system like this and that if metal at both ends is grounded it will be ok to have short lengths of un-grounded tubing inbetween.
So, may I present three questions for consideration in this forum:
Do members agree that all plasric components of a dust collection system should be grounded?
If so, how do you do it?
Finally. Galvanized duct held together with sheet metal screws adds the risk of an errant metal fragment hitting the sharp inner tip of a screw, and causing a spark that way. Which is the grsater risk, a static spark or a metal contact spark? (for now I have resolved NOT to use the dust collector as a vacuum, but reserve it for tool dust collection where, hopefully, there will be no metal fragments shooting down the duct.)
-Massey
Replies
Static
Apparently it is not easy to cause a fire/explosion from static buildup in PVC piping. Something about the speed and volume of the air moving through and getting the right concentration of the right particle size is very difficult to obtain, particularly in a small system with small pipes like a garage workshop. I think there is a FWW article called PVC Pipe Dangers Debunked or something similar that covers it.
Grounding the plastic in a dust collection system is usually to prevent the user from getting zapped from the pipes, in which case the ground wire can be wrapped around the outside of the pipe. Make sure this is well grounded so you don't build a giant capacitor.
Actually the clog of chips you are getting from your ground wire is probably a much bigger fire danger than the nigh impossilbe internal spark it is guarding against.
A spark on the tip of a screw is also very unlikely at the speed and force that materials move in a dust collection system, particulary in a 5 inch pipe on a home system. For proof, try to get a screw to spark against something by throwing it:)
Realistically, the biggest fire dangers in a dust collection system are things like sucking up a burning ember from a tablesaw, maybe sucking up sparks from grinding a chisel on a belt sander, overheating the dust collector, a screw hitting the impeller, etc
Dust collection and grounding
Thanks for that helpful response.
Rod Cole's article on Grounding PVC and other dust collection systems is interesting and his presentation seems both well reasoned and comepelling. The link is http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html
Best regards,
-Massey
Static
I've been a woodworker for over 40 years, and was a firefighter for 31 years. Never saw a fire in a woodshop contributed to static sparks. Dust explosions are a real danger, in the right environment. Home woodshops don't generally create enough of the properly sized dust particles to be of concern. The static shock is more of a nuisance than a danger. I'm with hack, I believe the greater concern is the inevitable clog that results from the debris trapped by the inner wire.
As the old saying goes, never say never. But internal grounding of your dust collection isn't necessary.
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