Static shock?


chrisphr
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So yesterday I was using an RO sander attached to a shop vac and decided to detach the vacuum hose from the sander (sander off, but plugged in, vacuum still running). One hand on the hose and another on the sander which has a totally enclosed plastic body. Just as I detached the hose I got one heck of a shock. It didn't feel like the snappy static shock you might get from rubbing your feet on carpet, more like a 110v shock you might get from a plugged in appliance.

This happen to anyone else out there? I suppose if it is static electricity, it shouldn't be that dangerous, just want to be sure it isn't my sander malfunctioning with electrical arc. Here is my setup:

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I touch my cats to drain the charge...  :ph34r:

 

I get pretty serious static discharges in the dry days of winter from plastic hoses here in CT.  Even my normally damp basement shop drops to 10-15% relative humidity.   It got worse when I switched from kerosene to electric heat.   Sometimes, larger pieces of sawdust and shavings will stand on end on the outside of the hose. 

 

Anything you can do to increase the humidity will go a long way towards reducing static buildup.

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It is funny but, I just had an experience with static electricity last month. It has nothing to do with woodworking except it happened in my shop.

I have an indoor/outdoor thermometer in my shop and I put  mylar window tint on the outside of the windows in the summer to block some of the heat from the sun. Of course, I peel off the tint in the fall so that I can get the heat in the winter. Well, last month as I was removing the tint, which is held in place by static electricity, I noticed the wire to the outside piece of the thermometer near the window on the inside of the shop was just dancing around like crazy! YEP! The static from the mylar tint FRIED my thermometer in and instant!

I've had that thermometer for 15 to 20 years and it worked just fine. I've installed the window tint for at least 10 years and never even thought about the static being harmful but, the stars were in alignment this time.:)

The good news is that my birthday was last month too so my wife bought me a new thermometer for a present and it is WIRELESS! :)

 

Rog  

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Rog,

Static window clings are responsible for job site fires. New windows come with protective clings that have all manner of warnings because individuals have stripped these clings in the presence of flammable cleaning solvents and paint fumes. The flash explosion fires are usually violent enough to break the glass.

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==> The volume of dust

To expand on PB, it's the volume, size of particles and their velocity. There are other factors such as volume of pipe, interior surface of pipe, etc, etc...

 

A dual-drum is a great example...  You get twice the fun... :)

 

Further, the second drum is typically a finer grit (giving finer particles), they create lots of particles per second, require high CFM/sfm to move them along the pipe, etc...

 

I've never gotten a shock from a dual-drum, but as PB says, it'll wake you up...

 

Come to think of it, don't believe I've gotten a shock from any of my stationary sanders... But did receive one from my planer (the DC ground wire running through the flex-connect came loose). It was impressive...

 

FYI: When setting-up a new stationary tool, I use a VOM* to measure continuity between the tool and the DC system to verify that the DC's connection grounding wire is in-place. The tool is left unplugged to prevent a false continuity reading...

 

 

 

*Volt Ohm Meter

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I had an old Craftsman shop vac with a spiral wire in the hose . As wear and tear exposed the wire on the outside of the hose the nasty shocking static got much worse! It had great suction for a cheap vac but was noisy as hell. I was glad to retire it . Anti static Festool vac hose purchase was an eye opener ! $130 for a 12.5 ft long x 36mm dia hose. Never had a shock from my Festool so that is nice.

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Rog,

Static window clings are responsible for job site fires. New windows come with protective clings that have all manner of warnings because individuals have stripped these clings in the presence of flammable cleaning solvents and paint fumes. The flash explosion fires are usually violent enough to break the glass.

 

Considering that I was on the outside of the shop and I seldom have that much paint or solvent fumes in the shop, I'm not going to worry about it too much.

It was a VERY dry day outside and I usually wash the window film before installing or removing it but, in this case the tint dried off before I got to it on that window.  I truly think that is what caused the extra static.

As I said, I've been installing and removing this tint for over 10 years and never noticed anything close to this before and I doubt that it would ever happen again.

 

 

 

In industrial grade situations, where large volumes of fine dust hang in the air, a spark from static discharge can set off an explosion. Suspended fine dust creates a fuel-air bomb. Adding a ground strap to drain off the static is a good practice.

 

I live in Kansas and both my grandfather and father worked in grain elevators all their lives and I am the first to admit that dust explosions do happen. However, I also know that in order to get an explosion of any real magnitude, there has to be so much dust in the air that a person cannot see or breathe in that space.

There have been dust explosions big enough to level large concrete grain elevators in the past but, they now have huge dust collectors to lower the chances of that happening these days.

If a hobby woodworker (or even a pro) ever gets that kind of dust in the air, he is working way too hard! :D  

As a Boy Scout I remember throwing a hand full of  flour into the campfire to watch the fire ball go up. Did you ever try that? It usually takes a good amount of flour and several tries to make it happen. Suggestion....Use a large cup or scoop and throw it high into the air!  :D  Don't ask me how I know.  :P

 

Rog

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I live in Kansas and both my grandfather and father worked in grain elevators all their lives and I am the first to admit that dust explosions do happen. However, I also know that in order to get an explosion of any real magnitude, there has to be so much dust in the air that a person cannot see or breathe in that space.

There have been dust explosions big enough to level large concrete grain elevators in the past but, they now have huge dust collectors to lower the chances of that happening these days.

If a hobby woodworker (or even a pro) ever gets that kind of dust in the air, he is working way too hard! :D  

As a Boy Scout I remember throwing a hand full of  flour into the campfire to watch the fire ball go up. Did you ever try that? It usually takes a good amount of flour and several tries to make it happen. Suggestion....Use a large cup or scoop and throw it high into the air!  :D  Don't ask me how I know.  :P

 

Rog

 

This is an interesting thing to discuss, because grain silo dust/flour are much much different from sawdust.  Sawdust, while still definitely flammable, is less likely to explode than flour (well most types of sawdust, there are some notable exceptions).  If you look at the sawdust cannon, he's actually got a flammable gas canister hooked up to the base: the sawdust serves to concentrate the gas, then the pilot light at the top triggers the chain reaction, causing the explosion.  The fireball is by far the trickiest part: once the sawdust has been superheated by the explosion, and ejected into a higher oxygen environment, the flames are able to race from grain to grain.

 

Has anyone tried this with the fatwood from longleaf pine??  

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  • 6 years later...
On 12/20/2013 at 8:05 PM, wdwerker said:

I had an old Craftsman shop vac with a spiral wire in the hose . As wear and tear exposed the wire on the outside of the hose the nasty shocking static got much worse! It had great suction for a cheap vac but was noisy as hell. I was glad to retire it . Anti static Festool vac hose purchase was an eye opener ! $130 for a 12.5 ft long x 36mm dia hose. Never had a shock from my Festool so that is nice.

I have that same festool hose which I use w my brushless DeWalt orbital sander and I just recently started getting a ton of static shocks, so much to the point where the sander will change speeds from the static, without having touched the speed dial (1-7) any suggestions to get rid of this?

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1 hour ago, Bunker said:

I have that same festool hose which I use w my brushless DeWalt orbital sander and I just recently started getting a ton of static shocks, so much to the point where the sander will change speeds from the static, without having touched the speed dial (1-7) any suggestions to get rid of this?

Is there a ground wire built into the hose that might be broken?

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Now I have something elso to worry about besides viruses!!!:(

Seriously, something about my one dog,s coat builds up static.  During obedience classes, walking on a foam pad floor, she would build up a charge and whenever I tried to treat her there would be a discharge from my hand to her nose.  She wanted the treats but knew that she was going to be zapped - a pitiful sight to see.  I took and old leather leash and wove and copper wire into it with one end attache to her collar and the other in my hand.  No more shocks.  True story.

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