@John Morris You are talking two systems. The DC motor is sealed and grounded and the ducting is a separate entity . The wire does need to be naked. As Lew stated outside will work.

 

My experience is I started with wire in side and switched to outside. Finally got tired of moving it with every duct changer and removed the wire. There is no know incident of an explosion in home shop. The dust is not at a high enough volume to create a problem in a home shop. My duct is 4 inch PVC and some dust does cling but have never had a shock.

Now Gerald. Of course you have never had an explosion. You wouldn’t be here to talk about it 😎

Paul

I agree by the way. I’ve never heard of a home shop explosion. 
Paul

I don't think  it is the wood dust

I think you have something hinkey  going on with the electrical.

But you can rule me  out by running a grounded wire through your dust hose into the vacuum tank.  If the static  accumulation ends then  it's the dust.

Thanks @KevTN for asking the questions and posting pics. Good thread. Thanks for all the responses too.

On 11/7/2021 at 9:54 AM, Masonsailor said:

The copper wire will be inside the ducting. One end will be grounded using the above mentioned methods. The other end doesn’t need to be attacked to anything. To keep it in place disconnect the duct from your tool and run the wire out of the duct and use the clamp on the duct to hold it in place. 
Paul

The copper wire have to be coiled inside the tubing or can it be ran straight through?

No need to coil it. Can be run straight.

2 hours ago, KevTN said:

The copper wire have to be coiled inside the tubing or can it be ran straight through?

Only need to coil if it's on the outside to maintain surface contact.

My .02$, TyWraps/wireties! I’d also get some fine stranded copper, or welding cable copper, so it will bend easily with the hose. Tywrap it every 4 feet or so.

Several of the woodworking supply outlets have unshielded, stranded copper wire. Probably less expensive, per foot, from a wire/electrical company

You might consider Stranded/Braided wire as an option.

Edited November 11, 20214 yr by Grandpadave52

My "day job" back when I was a slave included designing industrial exhaust systems, including wood shops (and including lead dust, flour, sugar, surgery centers, hospitals, AIDS labs; all the fun stuff).  About a decade ago, reading concerns on wood dust explosions, and hearing stories of getting zapped by static, I did some searching about wood shop fires.  Everything I found (notice:  only what I found) cited accumulated wood dust/shavings catching on fire due to a spark, but no explosions.  I think getting wood dust to explode is pretty tough to do.  But if you get the right combo of static build up, and you have a magnetic personality, you might hate getting zapped.  Might ruin your pacemaker, too?  (I never researched that).

     On the basis of avoiding nuisance, static electricity:  yeah, it's related to the materials rubbing together, and moisture, and conductivity of materials.  I imagine it is more prevalent in flex hose because you get more tumbling action on the rough duct surfaces (smooth ducts = less friction = less static) (engineers always reduce everything to formulas!).  Plastic doesn't conduct electricity, but you can ground it if the ground wire contacts enough surface area; I don't like putting anything (such as grounding wire) inside a duct, but if you wrap a bare copper wire around a plastic duct, it will draw off accumulated charge.  I connected the wire to the metal body of the dust collector.  In most cases, you can connect a duct grounding wire to almost any metal body that weighs a few pounds, and the static charge in the duct is "shared" with the metal, reducing the voltage/potential to a non-zapping level.  The charge eventually bleeds into atmosphere, aided by moisture.  [Spritz your shop?]   You can also run the grounding wire to an electrical outlet ground (metal body receptacles should be grounded).  Metal pipes usually eventually touch the ground and bleed off the charge.  PEX piping...well, probably not, right?  Grounding rod?  Uh, yeah, but maybe that's a bit over the top.

     I've never looked into the design of small dust collectors,  but the big ones (3 HP to 3000 HP) are required to be "non sparking" (AMCA-C used to be the criteria), where the fan blades, shaft and housing are designed to prevent sparks (usually by using aluminum on some parts), and the electrical gear is out of the dust stream, or rated XP.  The bigger the system, the more varied the conditions, and thus a greater likelihood of a spark/dust interaction.

     Most actual dust explosions I've heard of are in flour mills where the right combo of dust fineness, and dust/air/oxygen ratios are just right, and bingo your grain elevator disappears.  Sugar can also "rapidly combust", but the conditions are really rare.  In fact, most materials can combust if you work hard enough to cause it, but in real life situations, it don't happen much.

     I don't like screws sticking into duct, and it used to be Code didn't allow it.  Use rivets on small connectors.  Big ducts are joined by flange systems that have little interior texture that would hang particulates.  

     I'd spend more time concerned about breathing that dust rather than fearing its combustion.  Get a bag rated "1 micron".  It's not a scientific rating, but it does a much better job than the standard bag (which is usually characterized by 3 or 5 micron performance).

The way Pete explained it is always what I've been taught/told/led to believe. The chance of fire/explosion is nil, if the dust is thick enough in the air to explode...you are probably already dead from suffocation. Chance of fire from static is equally extremely low. But the static shock can be a real nuisance, and grounding may help with that. Otherwise (my opinion) grounding is a jumbo PITA. I grounded my first system (at the suggestion by Wood magazine) and every time I made a change it just doubled the work....so much so I quit doing it.  As you add/change tools or revamp the layout the ductwork has to be changed to accommodate it. Back to grounding it... if you must, Artie's suggestion is the probably the way I would go.

After reading all these great comments, I went back to look at Kevin's pics.  Boy does he have an issue here!

I'm a pretty electric guy, I'm surprised that I don't get zapped when he unplugs his hose to clean up!

It looks like he is using just one long 2" flex hose with a shop vac.

If this were my problem, I would first try some bare copper wire on the outside.  Putting it inside would likely cause chips to catch and then it is plugged.  Run the wire on the outside and tie it off every 4-6".  I would probably just use the wire itself and loop it around and get a good tight attachment and then on one end a length long enough with an alligator clip to attach to the miter saw or table saw.  I noted the static build up on the miter saw is just at the plastic knob on it, not the whole saw.  Might even experiment with the miter saw and see if it makes a difference in whether it is plugged in or not when being used as the ground.

 

One thing is for certain, Kev sure gets a static build up!

Edited November 11, 20214 yr by Cal
Added pic

9 hours ago, PeteM said:

   Most actual dust explosions I've heard of are in flour mills where the right combo of dust fineness, and dust/air/oxygen ratios are just right, and bingo your grain elevator disappears. 

My son worked for awhile at a grain elevator.  They had an explosion that killed several workers.  When they were allowed back to work, he said you could still hear the screams of the workers that were killed in the tunnels.  He found another job.

Pete that is good information thank you. 
 

Cal that picture is with the saw unplugged. That picture was with only the planner plugged into a power strip. The dust collection was plugged into a completely different power source. It bit me just as hard as when everything was plug into the same source. Lol This the first time this has happened.

On 11/10/2021 at 12:50 PM, KevTN said:

can it be ran straight through?

Ideally  it would be a grounded metallic duct.

But a single wire  laying inside the ducting should do the job for the purposes of trying to solve for  what's causing the problem.

 

Here's the thing.

Physically it is considered impossible to get the level of static AND oxygen AND fine particulate dust to get a fire started. That's for industrial applications where the flow and the volume are enormous.

BUT, "considered impossible" is not some iron clad guarantee.  I think it's not going to happen. But there are the occasional outlier events.  Mileage may vary.

That's pretty much why I think it's not the Dust collection. I could be wrong.  I am no expert and I didn't sleep in a holiday inn. 

 

You don't have an installed ducted  home DC,  But for those thinking about it.  Go with Metal Grounded Ducts.

Not because you are concerned about a static fire but because if there is a fire (from any cause) and the insurance adjuster wants to  get the insurance company off the hook and he can say it was the DC  then he may do just that and  you won't be covered unless it is metallic grounded Ducting.

If ya wanna go poly give your insurance agent  a call and ask straight out.

 

 

 

 

 

Thanks Cliff fire or no fire that is the most I have been shocked in I do not know when. Fire be damned I just want feel my fingers when I am going to use saw or jointer 

After all this great discussion about static electricity build up it became an issue here yesterday while using the shaper origin. The SO requires more suction that the DC system can provide so I use a shop vac to provide the dust collection. Up until yesterday all worked well but the SO has had a quirk in that occasionally the on board computer glitches and gives an error message that involves restarting the machine/computer to resolve. Very annoying. Yesterday it became a huge issue as the error message was occurring after every few minutes of operation. I just happened to notice that when the shut down occurs I was getting a slight static shock from the machine and ultimately the vacuum hose. It turns out that the static build up, the shock to my fingers (slight) and the shut down were happening simultaneously. Turns out the SO, although grounded was not able to tolerate the static discharge. I wound a copper wire around the vacuum hose and grounded it and all problems ceased. Here is a question for everyone. Can anyone see a downside in taking a three prong plug, cutting off both of the power prongs, leaving just the grounding pin, attaching a copper wire to the grounding pin lead and then using that to wrap the grounding wire around the vacuum hose ? 
Paul

13 minutes ago, Masonsailor said:

Can anyone see a downside in taking a three prong plug, cutting off both of the power prongs, leaving just the grounding pin, attaching a copper wire to the grounding pin lead and then using that to wrap the grounding wire around the vacuum hose ? 

That is the basic concept of computer antistatic grounding straps. Instead of destroying a good plug, get a banana plug and connect it to the copper wire. The plugs are available at electronics stores