My name is Mike I'm new here, could someone tell if you have to run
braided wire through pvc pipe that is hooked up to a dust collector so
that static elec. don't cause a explosion or fire, some guy at Home
Depot said I had to do that, is this true?
Thanks for any help!
That has turned out to be a popular urban myth. It has been discussed
here and on other forums many times and no one has ever been able to point
to a case where lack of grounding caused a problem. Cheers, JG
On Wed, 1 Feb 2006 01:10:08 -0600, firstname.lastname@example.org
Not common. But do keep in mind...
Fuel(wood dust) + Oxygen(air) + Heat (spark) = fire
I was getting static shocks on my tablesaw until I grounded my DC pipe
to it. A small wire will work, it doesn't have to be braided. I
think using metal tape is even better--fewer places to catch chips.
Well, anyone who knows about the defunct Soo Line (CN now), deserves a
Grounding an insulator isn't possible. In order for a ground to work, there
must be some conductivity to get those electrons to the wire.
Then there's a really narrow set of physical circumstances required for a
dust "explosion," which include extremely small particle size, extremely
dense distribution, and an instantaneous ignition source.
Tempest in a teapot.
I can not find the link, but one of the wood working magazines on the
web did a researched artical on this. They concluded that the ground
was not needed and if not done properly, the ground could increase the
chance of a spark. They also stated that the risk of fire is much more
real than the chance of an explosion.
I do not run any ground in my unit and I feel comfortable with that
after reading the available data I found on the subject.
Of course it is - and it's regularly done for dust collectors. You can
either apply a conductive surface coating or you can make the insulator
conductive (usually by mixing carbon black in with the plastic used for
moulding it). The monitor you're reading this on right now is very
probably insulating plastic with a conductive coating sprayed on the
Insulators are also conductive - if we're talking about real-world
materials in real-world environments and static discharges. A "brush"
discharge (the sort you notice) is formed when an "insulator" has a
surface coating of moisture, dust or similr on it that's insulated
enough to allow a charge to build up, but potentially conductive if it
can be induced to break down when a discharge starts. Purely insulating
surfaces don't store enough charge to provide a noticeable discharge,
it's these surfaces on the boundary that make the big discharges you can
In woodworking workshops though, static discharge is just a nuisance
problem, not _ANY_ explosion hazard. It will be worst on metal pipe
sections separated by insulators, so if you have any of these (Y-joints
maybe) then it can be worth earthing them. You only need an external
wire, not an internal one - although some people advise these "to earth
the flowing dust" (ridiculous), wood dust is also abrasive enough that
you'll wear through the wire before long.
Of course it is (although you may have only affected the surface, not
the volume) - but your original statement "Grounding an insulator isn't
possible." is far too simplistic. There _are_ things you can do to
reduce charge build up on insulators. The issue under discussion is that
it's not worth doing this, not that it's impossible to.
Let us know when your conductive anti-static coatings are able to tolerate
the abrasive effects of shop crap running through them, won't you?
Until then, there is a reason why they call it "static" electricity....
My dust collector's impeller housing has a bulk resistivity that's
similar to that of anti-static plastics in the electronics industry.
Looking at the colour it's chock-full of carbon black. Obviously you
can't retrofit this, but it's an easy thing for the maker to specify -
quite possibly it's just in there as a cheap filler anyway.
Incidentally there are copper/nickel multi-layer platings that can be
applied to plastic and are tough enough to resist abrasive particles
going over them. I've no hands-on experience with these for wood, but
they're tougher than the simple sprayed paints.
Insulator vs. Conductor is a scale of resistance. In the case of a
"conductive coating", all that is done is making a slightly less
resistive coat that can conduct static electricity along it's surface
to keep a static buildup in one place from happening. There isn't
enough of a conductor to run a current through, just spread the charge
This same principle is used quite often in many ordinary things:
Fabric softener / clothing static guard
The pink/silver plastic bags that electronics come in
ESD static mats electronic technicians work on
the plastic pads roller chairs roll on in the office
coatings on monitor screens
Take the static guard for instance. It obviously isn't enough to make
your shirt into a "conductor", but it does allow static to dissapate
along the surface of your shirt so you don't shock yourself everytime
you touch a doorknob in the winter.
There can be a very large static buildup on the PVC pipe,
insulator or not. And the static can cause sparks and
therefore set off a fire.
A wire run along the length of the pvc pipe and grounded
will help. A screen or shield around it would be even
There are plenty of small particles in a typical woodshop,
and most of us have drawn a spark from a static charge.
A spark along a long pvc pipe could do a lot worse.
Now, a cheap low power dust collector might not draw enough
air to do damage. But my ancient Silver King shop vac
does. It can light up a neon lamp next to the plastic
No, it can't (search the archives). There's a limit on the discharge
energy you can produce from this setup and it's demonstrably not enough
to start a dust explosion in wood dust.
Mix solvent vapour in - different situation.
Suck up a spark or smouldering ember - different situation.
Strictly speaking this isn't even a "spark" (as these things are
categorised by electrostatic engineers).
Its been mathematically proven (by an MIT engineer if memory serves me) that
you can't move enough air thru a 4" pipe (PVC or metal) to generate enough
static charge to sustain a spark of sufficient duration to ignite dust. Its
just another one of those urban myths surrounding woodworking. You probably
have a better chance of generateing that dreaded spark by sucking a screw
thru your dust collector impellor.
On 2/2/2006 1:53 AM Max Mahanke mumbled something about the following:
Mythbusters did a thing trying to get a large enough static spark to
create an explosion on a PVC pipe. Couldn't do it with sandblasting the
hell outta the pipe. Minor zaps from touching it was all that was possible.
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