Preventing Static Discharge in Dust Extraction Systems

[Bryan Milham]

We hope to complete our move to a new home in about a months or so's time. And with the permission of the Good Lady I am to add Dust Extraction to the workshop (garage). To that end I have been looking up and learning what I need to know about such systems.

One thing that struck me was the idea of adding a Static Discharge (grounding) system - the wire sometimes run through the pipework.

Looking for information on why and how I came across the following website;

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

It's a bit technical in places but the bottom line is PVC (the ducting) is an insulator, so why ground it. And there is actually no evidence for the dust density actually achieving an explosive mixture and being set off by an undischarged static voltage.

The only thing you might achieve is to reduce the opportunity of being the path to ground if you were to touch the PVC ducting the same way as you might in crossing a carpet then reaching out to a metal doorknob..

[admalin]

Hi

As an electrical engineer(MIET) I can confirm you can't earth plastic which is an insulator.

What you can do is discharge any build up of static electricity by using a bare conducting material like copper attached to the surfaces.

This acts rather like a lightening conductor on chimneys.

I think this is rather extreme for a small woodwork shop, but may have an application in highly dangerous atmospheres.

I've been in touch with the camvac people today and will send you their leaflet in a PM. (I don't know how to attach something in Adobe format on here)

Tony Malin

[Nick Prince]

I have worked in electronics manufacturing all my life, where ESD is a real problem.  I have trained 100's of people in the problem, but I never really considered it an issue in the Workshop.

My first though is that the dust density in the workshop is no where near enough for air ignition.  With dust extraction running it will be even lower.
I use a blow torch for decorating with no fires (yet!), so a spark from ESD is even less likley.

The science bit...
The trick with ESD is to elimiante disimilar materials from rubbing / pulling apart from each other.  By disimilar I mean in terms of the Triboelectric series.
http://www.trifield.com/content/tribo-electric-series/
The further away the two materials are on this scale the more likely the risk of spark. (Rabbit fur in non stick frying pans = not good !)

High velocity air streams are also a problem, as the air is "moving" over the internal surface of the PVC pipe it gathers charge.  Luckily dust and fume extraction systems are very low (relativly speaking) velocity.  The charge in the air discharges as it exits the tube, so if you really want a belt and braces approach, wrap so tin foil around the end of the pipe and run a wire to the closest grounded surface (pipes, bolted down lathes etc).  Or you could disassemble a plug top and just use the earth pin.

Frankly I think we have more important stuff to worry about.