On Wed, 02 Nov 2005 19:23:39 -0500, Astriapo
wrote:


I bought a dust collector tonight. What is the idea behind grounding
the hose? I assume to reduce friction. So do I connect it to a pipe
and hook it to the tool itself or what?

Thanks...

The incorrect idea is that by "grounding" the plastic piping, static
charge can be eliminated.

When two things in contact with each other are separated, electrons
can be stripped from one of them and deposited on the other. In this
case, the objects are 1) the piping and 2) air/dust. If either or
both of the objects are insulators then the resulting electrical
charges have no place to go and thus remain in place, i.e. they are
"static."

If the process is continous, as it is when air/dust is flowing through
the piping, the charges continue to build. They cannot build without
limit however because there is no perfect insulator so when the
potential difference (voltage) becomes high enough the insulative
properties will be overcome and the charge will discharge. This can
happen rapidly, via a spark (think lightning) or more likely, by
gradual discharge.

The myth in woodworking is that "ungrounded" piping will generate
static charge buildup sufficient to create a spark inside the piping
that will ignite the combustible dust. There is no documented
evidence of this ever happening.

Furthermore, even if there was, there is no way to "ground" an
insulator. It's an "insulator", by definition a poor conductor of
electricity, and attaching a wire to it, or running a wire through it
cannot prevent the buildup of charge in areas not directly in contact
with the wire. The best this wire can do is to insure that the
equipment at each end is at the same potential, something that should
already be the case due to the equipment-grounding conductor in the
power wiring.

Can you be shocked by static charge buildup in your shop? Sure. I'm
in AZ where the RH can be under 10% and dry air is a better insulator
than damp air. If I'm wearing rubber soled shoes and vacuum up a large
volume of dust, using my all-plastic (double insulated) vac, the
vacuum and I get charged up. If I then touch the metal frame of a
piece of grounded equipment I will get a shock. There might even be a
tiny spark. Does anyone think that this spark will ignite the dust in
the air and burn down my garage?

If I turn off the vacuum and wait just a few seconds, I can touch the
grounded equipment and not be shocked. This shows that the insulators
are not perfect and that the charge is slowly dissipated. Note that
this is a continuous process, which is why you don't get shocked every
time you run a vacuum; if the charge buildup is small, for example
when you're not sucking up sawdust, but just air, the charge is
dissipating as fast as it is generated.

Tip: If possible (and I remember to do it) I just keep one hand on a
piece of grounded equipment when I suck up a pile of stuff. Absent
that, I bend over and touch the concrete floor with a bare hand before
touching anything else. This dissipates the charge slowly and
painlessly.