Bad Science in Latest Wood Magazine

[allen long]

I noticed this issue of Wood magazine awarded the tip of the week to a person who came up with an elegant way to ground PVC ductwork. The problem is that you cannot bleed a charge off a non-conductive surface unless you have a grounded conductive material that covers the entire surface.

Even if you cover the entire surface of the ductwork, the static charge of concern is being generated on the inside of the ductwork. Running a grounded wire or a strip of conductive tape along the inside of the PVC ductwork will not work either.

If you are really concerned with static charge buildup and discharge, you are going to have to use ducting that is conductive (i.e., metal ductwork)

I am tempted to propose to WOOD to write an article for them explaining the science (based on experience in the aerospace industry (including analyzing propellant casting and handling)

Does anyone have any experience with WOOD and whether they would be receptive of such an article? Or is the grounding of PVC ductwork a myth that will never die?

Many Kind Regards . . . Allen

[glenn bradley]

I did not read the article but, in our forum vernacular when speaking of grounding PVC ducting I believe it is commonly agreed that we are talking about providing a ground source that will allow a static discharge. As you mentioned about it never dying, I don't even find that I react anymore when someone says "ground my ducting". I just assume they mean provide a ground for the static charge to drain toward.

That being said, I would hope a magazine like Wood would be interested in hearing about the science behind static charge and the ways that it can be discharged. There's certainly no harm in contacting them and making the offer. Who knows it might lead to other articles. I would certainly read it with interest.

[allen long]

I believe we are talking about the same concept. Any connection to the PVC to discharge or bleed the static charge will only bleed the charge at the attach or contact point. Since the PVC is non-conductive, there will be no bleed from the PVC surface over to the attach point. Every part of the PVC surface area that is not in direct contact with the conductive bleed line, will retain static charge.

Many Kind Regards . . . Allen

[Bryan Lisowski]

If you have the magazine in front of you there is probably a listing of how to contact the editor. I would think they would want to hear about the information so that they can educate their readers. I'm sure if they aren't interested, I bet enough members here would like that information.

[Van Huskey]

There are two main issues here, one the potential for static discharge inside the PVC "duct" causing a dust explosion and the second being static discharge from the outside of the pipe to humans. The first is theoretical the second certainly does happen. This is an area akin to religion within the woodworking community and no amount of proselytizing will change most people's minds given the years of conflicting information. IMO it is an area that unless you just like vying for the Don Quixote award it is better to save your breath or bits and bytes.

[Larry Edgerton]

May be bad science, but it works. I was helping someone out at their shop and the had a plastic pipe that would make so much static it would jump three feet and zap me. Took a bare copper wire and wrapped it around the pipe, screwed it to metal on both ends, and no zappy. Worked for me.

[Larry Frank]

This is an issue which never dies....

I want to see the three foot spark....how do I make one.

[scott spencer]

From my experiences, I think they might be open to the information. IIRC, they've had a change in editor in the past couple years, but I'm not positive. Can't hurt to approach them!

[Frank Pratt]

Yes, it sure does work. We wired up a rubber grinder for a retread plant & it had a 12" PVC duct that created tremendous sparks. Spiral wrapped it with bare copper wire & grounded it & no more sparks. There was still some static build up that you could see by the way the dust stuck to the pipe, but not enough to bite you when you got too close.

[Larry Edgerton]

This is an issue which never dies....

I want to see the three foot spark....how do I make one.

Ten horse dust collector/plastic pipe with a ton of chips going through it. You do not want to experience it, It actually hurt enough that you have an involuntary jerk every time you got hit.

[John Lanciani]

Ten horse dust collector/plastic pipe with a ton of chips going through it. You do not want to experience it, It actually hurt enough that you have an involuntary jerk every time you got hit.

It takes in the neighborhood of 2.7 million volts to cross a 3' gap in air. (the generally accepted dielectric strength of air is 3kV/mm). I don't doubt that you were getting static shock from the ductwork, but a 2.7 million volt 3' long arc generated by a dust collector is on the far reaches of plausibility.

[Larry Edgerton]

Quite possibly it was less than 3', its been a few years. It ran over my head and kept zapping me in the top of my head. But..... My point was not the distance but rather that rapping the copper wire around the pipe stopped me from getting shocks.

[Andy Giddings]

Can understand the desire to prevent static build up (regardless of whether it works or not), but if they are doing it to prevent explosions in a hobbyist setting I thought that had been debunked? See this article http://www.woodcentral.com/articles/...cles_221.shtml

[Van Huskey]

Can understand the desire to prevent static build up (regardless of whether it works or not), but if they are doing it to prevent explosions in a hobbyist setting I thought that had been debunked? See this article http://www.woodcentral.com/articles/...cles_221.shtml

That was what I was saying, there are two issues, one "doesn't" happen in small shop settings and the other definitely does. The static to human discharge is consistently said to go away with grounding by wrapping wire (or foil) vs something just at the end of the pipe, which "should" not work.

[Mike Henderson]

Can understand the desire to prevent static build up (regardless of whether it works or not), but if they are doing it to prevent explosions in a hobbyist setting I thought that had been debunked? See this article http://www.woodcentral.com/articles/...cles_221.shtml

That's a good article. Thanks for posting that.

Mike