Subject: PVC Pipe & Static Electricity in Dust Collectors

From: Chuck Steger <[email-masked]>
Date: Tue, 11 Feb 1997 15:05:06 -0500

It has been written about many times here in rec.ww but I have yet to
see a definitive answer on why wrapping grounding wire around (outside
of) PVC pipe will take static elctricity to ground. After all PVC is
nonconductive pipe so why would wrapping the wire on the outside of the
pipe work?
   Lo and behold, the April 97 issue of "Wood" magazine states this very
thing as one way of grounding using PVC pipe (the other way has rivets
going into the pipe wall). However, they did not mention why this will
work given the nonconductive properties of PVC.
   Can anyone explain why this will work (I've written "Wood" with the
same question but have not heard back from them yet)?
-- 
Chuck Steger
Warrenton, VA  
[email-masked]

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From: Termite <[email-masked]>
Date: Tue, 11 Feb 1997 15:47:32 -0500

I don't know, but think about this. The copper wire is conductive and
when the static charge builds up on the PVC pipe (and we all know that
it does, and big time) to the point that it will travel, it will jump
onto the copper wire and travel back to the point that you've grounded
it. Thereby discharging the static buildup on the pipe. 

You may or may not know, that without this grounding system that you are
exposed to an expolsion or fire. This could happen when the air is full
of fine dust and a static charge JUMPS from the pipe to a metal surface
setting off a small spark in the process which ignites the dust - High
levels of fine dust are very volitle (sic).

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From: [email-masked] (John Paquay)
Date: 11 Feb 1997 22:07:54 GMT

In article <[email-masked]>, [email-masked] says...
>same question but have not heard back from them yet)?

The static charge builds *because* PVC is a non-conductor.  It's the
same effect as the old rabbit fur and acrylic rod demonstration. (Or the
latex balloon and your hair).  The wire collects the charge and allows it
to ground, which is something the PVC cannot do.

-- 
John Paquay
[email-masked],  [email-masked]
http://www.physics.purdue.edu/~jep/
-----------------------
Without my wings you know I'd surely die...

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From: "David Misevich" <[email-masked]>
Date: 11 Feb 1997 22:33:17 GMT

snip...

>why wrapping grounding wire around (outside

I don't have much experience with static electricity, but at work we used
to test insulators with a step-up transformer. The process is called
Hi-Potting, and if you get the voltage high enough, even "nonconductors"
will allow electricity to flow through.

This could explain why static electricity (very high voltage, low power)
will dissipate through the wall of the PVC. This would be kind of like the
surge supressor on the power line of your computer.  There is a device in
there called a MOV that will not pass current until the voltage gets to a
certain level, and then it conducts and dissipates the voltage spike.

Dave

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From: [email-masked] (Explodey2)
Date: 12 Feb 1997 03:37:28 GMT

I has largely to do with the fact that although the pipe is not a
conductor, it can still build and hold a charge. Just like your carpeting
is not a conductor, it can also build a charge. Static charge tends to
build or accumulate on the surface of an object, thus wrapping the pipe
will help to "drain off" any charge which begins to build on the surface.
You're not using the pipe as a conductor. What surprises me is that no one
has introduced anti-staitc pipe. Let's face it PVC may well be easier to
use and install than metal and it isn't that tough to make plastic
conductive by adding carbon black to the formula. Maybe not enough demand?

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From: Skip <[email-masked]>
Date: Tue, 11 Feb 1997 22:52:54 -0500

> same question but have not heard back from them yet)?

It's a capacitive effect, which builds up a charge on the outside as a
charge is building on the inside. The dust inside is building the
charge, so a wire is needed inside, and for small areas that may build a
charge (like on the opposite wall from where the wire happens to be),
the outside wire dissipates any outside charge before arcing to some
grounded thing in the shop happens. The outside wire in use is really
overkill though (IMO) and I've had no trouble running with only an
interior wire, testing the outside for buildup shows none occurring.

Skip

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From: Ernest Shipley <[email-masked]>
Date: Tue, 11 Feb 1997 11:57:00 -0800

> same question but have not heard back from them yet)?
Well, lets see if I can take a stab at this. "Almost" anything can get a
static (meaning non-currentflowing) charge on it, whether it conducts
electricity or not. But bringing the item in contact with a good
conductor of electricity (the copper wire) connected to ground and the
"static" charge will bleed off through the wire to ground. Want proof?
Simple. The plastic comb thing--run through your hair and it crackles
and pops as it builds up a charge, right? Wrap a copper wire aound it
and connect it to ground (water fawcett) and no more charge. Clear as
mud, right?
Ernie

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From: [email-masked]
Date: 12 Feb 1997 15:11:24 GMT

Other comments on this have included running an outside wire with
pop-rivets through the PVC every 2 feet.  The wire of course goes to a
ground.  I'm going to use that approach on my 1HP that goes from flower to
flower like a bee.  Also have shop built cyclone tween tool and DC.