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John Grossi
12-14-2007, 8:35 AM
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
12-14-2007, 8:57 AM
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
12-14-2007, 9:09 AM
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
12-14-2007, 9:43 AM
Here's the link to that article:

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

Be well,

Doc

Kyle Kraft
12-14-2007, 9:54 AM
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
12-14-2007, 10:08 AM
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
12-14-2007, 10:29 AM
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
12-14-2007, 12:26 PM
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
12-14-2007, 12:34 PM
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
12-14-2007, 12:55 PM
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
12-14-2007, 12:57 PM
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
12-14-2007, 4:11 PM
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
12-14-2007, 5:25 PM
"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
12-14-2007, 6:19 PM
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
12-14-2007, 11:28 PM
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.

Ken Fitzgerald
12-15-2007, 12:10 AM
Static electricity and dc have been a long debated topic...here and at other sites. Some people have a difficulty separating theory from reality. In theory, it could be a problem. From everything I've read, there is no evidence that static elecricity has ever caused a fire in a dc used in a hobbiest shop. I'd be more concerned about a piece of hot metal spark going into the DC and eventually causing a fire.

That being said, my Oneida DC delivered Thursday evening. I bought my snaplock metal pipe from Oneida too. While I'm not worried about static electicity causing a fire, I don't find it pleasant to be shocked. That plus, I live in a fairly arrid climate. The total annual average moisture for my locale is 12". May and June are typically our wettest months. As such, I will experience static electricity much more often than someone say in the deep south, mid-west or the east coast. I wear slacks and dress shirts to work daily and am constantly, year-round getting shocked as I get out of my car, which I often do several times a day as I bounce from hospital to hospital. For that reason alone, I decided on metal pipe...not because I was worried about static electricity causing a fire.

There are a lot of folks who successfully use PVC.

There are a lot of folks who successfully use metal.