Thread: Are the PVC users here not earthing any more?

Maybe you're not allowed to anymore unless in possession of an electricians licence.

Seriously though, static buildup potential can be minimised with knowing how it works and some planning. I can see potential spontaneous combustion if a stray spark takes advantage of flamable fluids or sawdust etc. but have never heard of it happening.

Here's a fairly technical explanation - The TriboElectric Series

It includes a table of materials and values which indicate how likely they are to cause static discharge.

Keep cats away from rubbing on your ducting (and keep flamables stored safely) and it should be ok.

I would think that if you have so much dust floating around that a static discharge could light it up into an uncontrollable combustion, then you already have some other serious issues with your dust collection system.

Imagine how many guys are grinding metal occasionally in their wood workshop and that might help put it in perspective.

Screw the PVC to your grounded steel shed. If you are not getting zapped from it when standing in bare feet then it's unlikely that enough elecric potential is being built up to start a fire.


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Fundamental physics says that as soon as any tiny electrostatic charge is generated it moves as far apart from other like charges as it can. The furthest apart it can get is on the outside of the object where if it discharges to ground is unlikely to cause a fire as the fuel air ratio will not be right. Same reason you are safe in a motor vehicle during a lighting storm and it has nothing to so with the tyres. This means the chances of enough charge building up inside a PVC duct to cause a spark is extremely small. I will not say it will never occur but the risks are much more likely you will cause a fire in your DC by other means well before this happens.

The thing is that being an insulator you cannot completely ground PVC anyway and it is capable of holding quite a high charge on one end or area whilst being grounded just a few cm away. It depends how damp and grubby the outside of the duct is.

The most likely cause of a DC fire is sucking up a hot object and there has been a recorded case of this leading to a significant fire.

Fire has been reported inside sparking metal ducting when an object has rattled its way down the duct creating sparks by collision with the metal.

Originally Posted by DaveVman

I would think that if you have so much dust floating around that a static discharge could light it up into an uncontrollable combustion, then you already have some other serious issues with your dust collection system.

Imagine how many guys are grinding metal occasionally in their wood workshop and that might help put it in perspective.

Screw the PVC to your grounded steel shed. If you are not getting zapped from it when standing in bare feet then it's unlikely that enough elecric potential is being built up to start a fire.


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I had never thought of it causing a problem on the outside of the ducting Dave. I imagined the danger was on the inside where all the dust was shooting down the pipes. My system took all the dust fro the point it was created and bagged it . Most of the time.

Originally Posted by BobL

Fundamental physics says that as soon as any tiny electrostatic charge is generated it moves as far apart from other like charges as it can. The furthest apart it can get is on the outside of the object where if it discharges to ground is unlikely to cause a fire as the fuel air ratio will not be right. Same reason you are safe in a motor vehicle during a lighting storm and it has nothing to so with the tyres. This means the chances of enough charge building up inside a PVC duct to cause a spark is extremely small. I will not say it will never occur but the risks are much more likely you will cause a fire in your DC by other means well before this happens.

The thing is that being an insulator you cannot completely ground PVC anyway and it is capable of holding quite a high charge on one end or area whilst being grounded just a few cm away. It depends how damp and grubby the outside of the duct is.

The most likely cause of a DC fire is sucking up a hot object and there has been a recorded case of this leading to a significant fire.

Fire has been reported inside sparking metal ducting when an object has rattled its way down the duct creating sparks by collision with the metal.

Thanks Bob .
That's interesting info . The way I had the old one set up had the wire spiral wrapped around the whole of the first stage or the system , so there was a pass every few inches. So still not 100 % effective by what your saying . As I added a longer extension to it I got a bit slack and had no wire on that.

Sucking up a hot object would be a disaster. I did hear of a couple of big fires with blokes I met, and their dust collector story's . One Bloke was dismantling an old metal set up and the angle grinder he was told not to use in the contract of sale set it on fire and burned the factory down. I think the court case meant he had to live with his Mum 15 years longer than expected. Real nice guy as well.

The other was a bearing in the fan failed,over heated and had a melt down which sent white hot sparks in to the dust. The unit kept running long enough for the whole lot to go up and the factory burnt down. Another good reason to have the unit outside.

I was always worried about my old one as the whole thing was in a room under the shop and that was under my timber racks. So I had a habit of feeling the bearings on the fan for heat every now and then. It's a good old, Made in Fitzroy, Cast iron, Richardson fan . And the bearings never gave up thank goodness.

Rob

Originally Posted by auscab

Thanks Bob .
That's interesting info . The way I had the old one set up had the wire spiral wrapped around the whole of the first stage or the system , so there was a pass every few inches. So still not 100 % effective by what your saying . As I added a longer extension to it I got a bit slack and had no wire on that.

Sucking up a hot object would be a disaster. I did hear of a couple of big fires with blokes I met, and their dust collector story's . One Bloke was dismantling an old metal set up and the angle grinder he was told not to use in the contract of sale set it on fire and burned the factory down. I think the court case meant he had to live with his Mum 15 years longer than expected. Real nice guy as well.

The other was a bearing in the fan failed,over heated and had a melt down which sent white hot sparks in to the dust. The unit kept running long enough for the whole lot to go up and the factory burnt down. Another good reason to have the unit outside.

I was always worried about my old one as the whole thing was in a room under the shop and that was under my timber racks. So I had a habit of feeling the bearings on the fan for heat every now and then. It's a good old, Made in Fitzroy, Cast iron, Richardson fan . And the bearings never gave up thank goodness.

Rob

I use my dust extractor to grab metal dust from my various grinders and sanders.
The risk of a hot objet being sucked into the dusty is greatly increase so this is where I do use a dust separator.
The catcher is a 20L steel drum (Incidentally it originally held Lab grade Alcohol in it so cutting it open was interesting)
The spiral shiny ducting is Al located mylar and the arm supporting it all is SS
IMG_1615.jpg

SWMBO reckons it looks like a cheap alien from Dr Who.
IMG_1618.jpg

Originally Posted by BobL

I use my dust extractor to grab metal dust from my various grinders and sanders.
The risk of a hot objet being sucked into the dusty is greatly increase so this is where I do use a dust separator.
The catcher is a 20L steel drum

What is inside the 20 litre drum to stop the objects going back out . Mesh over the outlet or a divider down the middle?

Originally Posted by BobL

SWMBO reckons it looks like a cheap alien from Dr Who.

lol
Some of those cheap Dr Who aliens have had me freaked at times.

Originally Posted by auscab

What is inside the 20 litre drum to stop the objects going back out . Mesh over the outlet or a divider down the middle?

Nothing, The momentum of anything heavy (metal dust or hot metal object) combined with the much lower air speed inside the drum makes it fall out of suspension and it cannot be picked up again.

Originally Posted by BobL

The most likely cause of a DC fire is sucking up a hot object and there has been a recorded case of this leading to a significant fire.

+1 on that.

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