Thread: Earthing dust extraction

Hi Chief 012,

I've seen the arguments for and against earthing dust extractors with plastic pipe reticulation rattle round for many years. I've never seen anything definitive come forward on this and it certainly doesn't form part of the requirements of my insurer. I've been going along sucking dust most days for 27 years without any problem and without an earth in place.There's certainly lots of static there on the outside of the pipes:sufficient to make the hairs on my wrists stand up on end if placed about 100mm or less distance from the pipe.

That's all I know about it. Let us all know if you find the answer.

Old Pete

In terms of hobby and non-industrial DCs it's a myth that static electricity produced by PVC ducting will cause a fire/explosion. It is also physically impossible to ground PVC since it is an insulator so using the cable kits on PVC is waste of money.

For a technical discussion by MIT Physicist Rod Cole see here.

Fires do occur in DCs but the happen for other reasons like sucking in a lump of hot metal, overheating the DC motor etc

Thanks old pete & BobL, I think you have well and truly answered my question there!

From Rod Cole's article - I should be just as concerned about spontaneous compustion!

Many thanks

Cam

Inaddition Mythbusters did a segment on static in plastic pipes and possible ignition........BUSTED.

As I have posted before......no one has ever produced a single documented incident where there has been a dust explosion in small scale workshop dust extracion systems due to static electricity.

cheers

This question comes up a lot in discussion and planning systems. Systems vary, some suffer, mine certainly doesn't and no one seems to have any answers. An insulator can't be grounded, my system hangs from a metal roof structure and I have always wondered if that has anything to do with it never generating static electricity, I don't see how it can as that metal structure sits on a timber frame.

Got to love Mythbusters!

I did not earth mine and am happy to say I am still here to tell the tale

The main reason that a small cavity like PVC ducting does not generate a spark inside itself is because as soon as any charge builds up inside it the charge moves to the outside of that cavity so not enough charge builds up on the inside to generate a spark. Even if a spark is generate the air-dust ratio required for explosion are relatively narrow.

On a dry day it is possible to feel the charge on the outside of dusty ducting and it may give you a bite which is why some people like to ground their ducting.

With plastic ducting there is a miniscule chance that two chunks of say steel and stone will impact together or more likely that stone will strike the steel impeller and make a spark. Grounding of the ducting will do nothing for this potential problem and is one of several reasons not to use your DC as a vacuum cleaner.

In situations where large steel ducting is used the cavities are much larger, the air speeds often higher resulting in greater amounts of charge and there are often lots of sharp points near ports and junctions where a discharge may lead to sparks.

I haven't earthed mine, I have a combination of metal and plastic pipe, I do get a bit of static build up in the plastic pipes off the thicky but nothing that concerns me, I get more of a zap getting out of the car

The general concensus is you don't need to bother, if you want to do it for some piece of mind or don't like getting zapped, OK do it but I had conditions that if my DE was going to catch fire I had it here https://www.woodworkforums.com/f200/w...-there-135446/ and no fire/explosion.


Pete

Originally Posted by pjt

I haven't earthed mine, I have a combination of metal and plastic pipe, I do get a bit of static build up in the plastic pipes off the thicky but nothing that concerns me, I get more of a zap getting out of the car
. . .

Sorry to be pedantic but else one uses a particle accelerator, it is not possible to get build up of charge "in" plastic or inside a plastic pipe, it can only build up "on the outside" of the plastic pipe. I'm only being pedantic in case some newbie reading you post thinks it can build up inside the ducting

Originally Posted by BobL

Sorry to be pedantic but else one uses a particle accelerator, it is not possible to get build up of charge "in" plastic or inside a plastic pipe, it can only build up "on the outside" of the plastic pipe. I'm only being pedantic in case some newbie reading you post thinks it can build up inside the ducting

Nope, no particle accelerator here, I guess it's just one of those things that most of us say that isn't technically correct but is just said, like the difference between absorbed and adsorbed, most would know absorb but may not know adsorb and therefore say something like " the liquid was absorbed" into the cloth but in fact it may have only been adsorbed


Pete

Originally Posted by pjt

Nope, no particle accelerator here, I guess it's just one of those things that most of us say that isn't technically correct but is just said, like the difference between absorbed and adsorbed, most would know absorb but may not know adsorb and therefore say something like " the liquid was absorbed" into the cloth but in fact it may have only been adsorbed


Pete

Yep - I get that one confused from time to time.

The one possible use for grounding PVC pipe systems is avoiding the 'Youch!' effect when getting zapped by the static.

But no fire.

Um yeh it wont even do that.

Ya cant earth PVC because it is not conductive and parts will still build up charge.

There are arguments that attempting to earth a PVC dust extraction system actuall increses the hazards.

cheers