Static electricity?

[John Grossi]

Hi, Problem yesterday in my basement shop. I dropped my arbor nut into my table saw cabinet. I opened the door and noticed a lot of chips. I disconnected my Delta d.c. hose to sweep up the chips and got a pretty good shock when I touched the cabinet. Figured it was static electricity, but it got me thinking of a potential explosion. Anyone else experience this? I have noticed when turning on my d.c. I get a very small shock. Everything is grounded and wired to code by an experienced electrician. Any thoughts are appreciated. Thanks John

[Chris Foley]

John,

What is your DC duct made of? Is it a continuous ground also? If it is PVC, then you could have an issue. The code grounding that you speak of is what inspectors look for. The grounding you need is really industrial and a lot of inspectors do not know the difference.

All this said, I would verify that the bodies of your equipment are grounded as well as the electrical supply. They should terminate at the same ground rod. I spent 12 years designing and building large industrial equipment and this is one of the items that gave us fits when the UL folks showed up.

Chris

[James Phillips]

If you do not want the occasional shock, then ground your duct work. The charge that builds up is not enough to cause an explosion. I cannot find it now, but there is a scientist and hobby woodworker (from MIT I think) that researched this and has a webpage.

[Don Abele]

Here's the link to that article:

http://mywebpages.comcast.net/rodec/.../DC_myths.html

Be well,

Doc

[Kyle Kraft]

John, I'm not a scientist or anything, but from what I understand the conditions that can support a dust explosion are somewhat difficult to come by. Everything has to be just right, the size of the dust particle, the concentration, ignition source, oxygen availabilty, etc..

It seems to me that I remember a discussion on SMC related to this topic, and there were people with way more college credits that provided some good facts.

[Cliff Rohrabacher]

There are people who will chasten you and talk down to you for worrying about this.

I think it is an issue worth some attention. The fact is you need a minimum of air and combustible to get an explosive response and it's unlikely that you will get that in a home DC.

However, you can get a smoldering fire started. It's not common but it does happen and some time googling around will obtain pictures and information about the hazards.

It doesn't take a rocket scientist to realize that a good 50,000 volt discharge of static can ignite a bit of dust and that in turn can smolder and the air flow can assist it.

If I built a DC from PVC (or other non conducting material) I'd run a bare wire or two (any metal would do) through the length of the ducting and into the bin and ground it. I'd also ground the machine frames. in addition to whatever grounding the manufacturer has.

Seems little enough effort to eliminate a potential problem.

[warren kafitz]

A bare wire wrapped around on the outside of the pvc pipe it all you need to kill the static. Just connect one end of the wire to a ground.
Warren

[Burt Alcantara]

In my shop I get zapped when I vacuum any electrically connected tool. Same thing happens when I use the DC as a vacuum. All outlets and tools are grounded. I guess it goes with the territory.

No woodshop has ever recorded a dust explosion. Those events are for grain elevators, not wood shops.

Burt

[Andrew Nemeth]

I have a 1200 cfm Jet DC running into PVC pipe in my shop. I ran a bare copper wire inside the pipe and if I had to do it again I would run something else instead. The wire in the inside often gets large wood curls wrapped around it and I end up having to open it up to free the clog. If you are using non conductive components and can get away with wrapping externally I might give that a shot before trying to fish a line through the inside. If you do wrap externally let us know the results, I may end up wrapping mine and pulling the internal wire out.

-Andrew

[Steve Kohn]

Before I built my current shop/garage I used my 2 car garage as for woodworking. My dust collection was a bunch of 4 inch flexible plastic spiral hose without grounding. I routinely got zapped when I would touch any machine.

When I built my current shop, I used metal duct. I have even run wire around the plastic blast gates and between the ducts and machines where they are connected by flexible plastic hose.

No more shocking surprises. It is so nice.

[Steven Wilson]

You can get the same static shock with metal ductwork if you don't connect the wire that goes through your flex hose to your metal ductwork and machines. Something as simple as exposing a bit of the wire and bending it so that it touches the machine and blast gate will keep the charge from building. I use some quick release fittings on my flexable DC hose and I made sure to make those sonnections. Unfortunately the large hose that came with my Festool cleaning kit (not the small one for the tools) has no grounding wire and when I use it to suck up chips around the shop I will often get a nice zap in the winter - oh well.

[Lee Schierer]

I agree that other than the discomfort factor there is nothing to worry about. The amount of dust in the air needed for a dust explosion has to be so thick you can't see your hand. The link provided in the other posts is good info. Mythbusters (even though their science is up for discussion) tried unsucessfully to create a dust explosion several ways and their conclusion was it was much harder to do than it sounds. Particulate size has to be considerabluy smaller than most saw dust. Static shocks don't pack a lot of heat energy.

Personally I have pvc duct work in my shop and I have not been zapped for many years since I installed it. I saw some static build up the first few months after it was installed, but now the ducts won't even raise the hair on your arms if you get close to them. I have no grounding wires inside or outside. I vacuum the floor, run my sander into it while I'm sanding and have a planer. No zaps no static.

[Bart Leetch]

"Personally I have pvc duct work in my shop and I have not been zapped for many years since I installed it. I saw some static build up the first few months after it was installed, but now the ducts won't even raise the hair on your arms if you get close to them. I have no grounding wires inside or outside. I vacuum the floor, run my sander into it while I'm sanding and have a planer. No zaps no static".

I have a friend with PVC in his shop as well as my own shop & will second & third the above as a true statement.

Most DC fires come from someone using a single stage DC as a vacuum cleaner & sucking up a screw or other piece of metal the goes by the impeller blades causing a spark igniting the dust in the dust bin. In my shop the DC is just for the equipment & I have a shop vac to do the cleaning with.

[nick brigg]

I for one am worried about this static business after reading the posts. i'm setting up shop and have a single stage going, but havnt picked up a dust hose for it yet. what hose would i be looking for and how could i ground that hose so that i dont get zapped all the time?

[Bart Leetch]

I for one am worried about this static business after reading the posts. i'm setting up shop and have a single stage going, but havnt picked up a dust hose for it yet. what hose would i be looking for and how could i ground that hose so that i dont get zapped all the time?

If you can just set things up so your hose isn't where you brush against or bump into it. Of course my system is a 2 HP completely plumbed in with PVC & hose so I don't move the DC. My DC sets right by the door so its easy to empty it.

Most of my hose is behind or under or off to one end where I won't touch it anyway.

At that I have checked it out & after running either of my planers or jointer & after having used it off & on initially for about 2 weeks to a month I couldn't get it to zap me. I think that using it & getting it dusty must have helped stop it from zapping me.