# Grounding your Dust Collection System



## wstokes

So I've finally broken down and decided to get serious about dust collection. I picked up a Delta 50-760 1.5 HP (1200CFM) dust collection, 60' of Schedule 30 4" PVC pipe, and a ton of fittings, blast gates, flex line, adapters, wire clamps, PVC glue, wire, etc. etc. I now have all my PVC cut and fit together, ready to be glued, but I can't make up my mind: should I run wire on the inside to help ground the system? I already bought the wire and twist dealies and have decided I want to wrap the outside the pipe to help ground the system. A little book I bought on dust collection recommends drilling a hole an inch from each fitting and running a wire in the hole, along the top of the run, and then out the hole on the other end. I've read a few places online where people think this is nuts, that you'd need to have a lot more wire than that to have it be effective, and it's easy to increase the static pressure of your system and cause chips/dust to start to clog up on the wire. I suppose I could try to pull the wire super tight, perhaps tagging it with a small screw at either end, but even then I'm sure it'll dip a bit, especially in one very long 9' run over to my planer. Also, I found two people at Woodcraft both recommend I not ground the inside. They said I could, but talked about problems they had with such systems and in one case ended up ripping the wire back out later one, filling up the holes, and the system performed better than before. Oh, finally one potentially important tid-bit: I have setup a large metal trash can as a per-stage. Thus if I ever did get a fire started inside the pipe/system, it probably won't be able to reach the plastic bag for dust that actually makes its way to the impeller. So I'm curious what all you lumber jocks think? Should I just ground the outside?


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## papadan

What does the owners manual have to say about this? I installed a 2hp grizzly about 8-9 years ago and the manual said to ground the system with a bare wire inside the duct tubes, bring it out around the gates to keep from preventing thier closing. The end at the DC should be connected to a screw into the metal housing and each end run of duct should be connected to the tool being used. Just before the end of each run, I exited the tube and attached a section of stranded wire with an alligator clip on the end to clip onto whichever machine I am using. Lots of people say it is not nesc. to ground them, but the manufacturers say do it, and for as little cost and extra time as it takes, why not just do it and be safe for sure.


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## SteveM

Boy have I seen lots of answers to this question. I have no idea what is the correct answer but here's what I did. I ran metal HVAC tape down the inside of the PVC (no interference for the airborne dust) and connected it to a wire run outside the pipes. No problems after 4 years but I may have had no problems by doing nothing.


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## 33706

Regardless of whether grounding is necessary, I'd hate to explain to my insurance adjuster why I didn't ground my system, if there was a fire. That reason alone trumps the argument over whether grounding is necessary, or even effective. Do it!


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## rareddy

You cannot ground a non-conductive material (PVC). The only thing running a wire in the inside of the pipe will potentially do is help the pipe clog up. Not to mention that there's not ONE reported case of a fire caused by static electricity in a dust collection system.


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## rareddy

BTW, here's some good reading material on the subject:
http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html


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## TopamaxSurvivor

My guess is that is to keep people from getting zapped when they touch the collector pipe.


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## pvwoodcrafts

Oh geez, not here too!!!


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## papadan

Bob, you don't ground the plastic pipe itself, you are grounding the airflow through the pipe. Air flowing through the pipe can and will create static electricity, this static can be felt and seen in the way of a spark. As I stated in my post above, read your owners manual, if they don't recommend grounding, then don't do it. No need for any arguments here, each person is free to believe what they want. I personally follow the manufacturers recommendations on my equipment, I figure they now more than me.


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## papadan

Here is the current owners manual for a 2 hp DCsystem. Page 34 explains the method and reason for grounding. As stated, I follow the Manufacturers recommendations.


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## TopamaxSurvivor

That info from Grizzly is good standard practice for uniform grounds through any electrical equipment. There is also the possibility of equipment ground failure at any piece of equipment being connected to the system. I'm surprised they didn't recommend the bare ground be at least a #10 or 12.


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## Amac

Why not use metal tubing like you use for a dryer vent? Then you can just ground the the entire thing with one wire and no clogging issues from wires inside the pipe.


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## Dez

One person I know of used the "Metal" Aluminum duct tape and ran it inside the pipe. From my understanding it was not easy to do and I am not sure of the actual benefit. I have not heard of any fires caused in a home/hobby type situation, but I have seen and felt some pretty nasty shocks from ungrounded sections in my own dust collection and that was on the plastic flex that I used to connect the machines to my metal duct.


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## papadan

Andy, If I ever have reason to redo my DC system, I will use metal duct pipe for it. Anyone using thiers as a portable and hooking it up to one machine at a time does not need to ground it. Thier hose would only be a few feet long and not have enough action to build up a charge.


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## GaryK

Read Fine Woodworking issue 153 page 048 - *PVC Pipe Dangers Debunked*

An Article by Rod Cole

Home-shop dust-collection systems have become increasingly popular, but their safety has been hotly
debated. The primary issue is whether PVC pipe is safe for use as ductwork. Many claim that sparks in PVC pipe
due to static electricity may ignite the dust cloud in the pipe. The specter of a giant fireball consuming a shop and home is repeatedly raised. Others claim you can ground PVC, thus ensuring its safety.

Two years ago I had to decide for myself: PVC or metal ducts for my basement shop. Being both an avid woodworker and a scientist, I made a concerted effort to understand the issues. Fortunately, I have the resources of the library at the Massachusetts Institute of Technology (MIT) and a professor just down the hall who's an expert in the physics of lightning. I studied static discharge from insulators, as well as the more general topic of dust ignition. I found that it's extremely unlikely for a home-shop-sized system to have a dustcloud explosion. Commercial-sized systems have had dust-cloud explosions, but different phenomena come into play in larger systems, and 4-in.-dia. PVC is too small for use in such systems, where the airflow is much greater than in a home shop.

Sparks are unlikely in 4-in.-dia. PVC pipe In my research I turned to the Journal of Electrostatics, a publication
that covers the effects and interactions of static electricity, particularly in commercial applications. This journal 
has published a number of studies on the combustibility of dust clouds by electrostatic sparks. The researchers were able to determine some of the conditions necessary to create sparks and ignite a dust cloud.

Sparks can be caused by a variety of conditions-one of which is static electricity. However, sparks are unlikely inside
a standard 4-in.-dia. PVC pipe that would be used in a home shop, and more importantly, any such sparks are extremely unlikely to be strong enough to cause an ignition. I can't say it is truly impossible, but it is very close to impossible, and I do not know of a single instance.

The difference between metal and PVC is that one is a conductor (metal) and the other is an insulator (PVC). A conductor allows electrical charges to flow freely. If any excess charge is not given a path to ground, it can arc, creating a spark that in certain conditions can ignite a flammable substance such as dust. Grounding provides a path for this excess charge to flow harmlessly to the earth, which is why dust-collection systems in all commercial shops are required by code to be grounded. However, an insulator is a very poor conductor of electricity. While it's possible to get a static shock from the outside of a PVC pipe, it is highly unlikely for sparks to occur inside.

Dust collectors with 3 hp or less pose little danger I published my findings on my web site. Rob Witter, a representative at Oneida Air Systems Inc., which makes dust-collection systems, said he largely agreed with my research. "We as a company have been trying to trim away at these misunderstandings for years," he said. He added that plastic pipe will "probably never cause a problem" in a home shop. Finally, he pointed out that the National Fire Protection ssociation NFPA) puts no regulations on dust-collection systems of 1,500 cu. ft. per minute (cfm) or less.

All of this discussion applies to home-shop-scale systems. Larger systems, complete with ducts and filters that move
more than 1,500 cfm, require at least 3 hp and are not found in most home shops. Larger systems need larger ducts, and with that you have to begin to worry about more complicated forms of static sparks.

The real hazards In a home shop, the dust-collection fire hazards you need to worry about are not in the ductwork but in the collection bag or bin itself. A fire may be caused by a spark, which can occur when a piece of metal is sucked into the ductwork and strikes another piece of metal, or by embers from a pinched blade. The spark or ember settles into the dust pile to smolder, erupting into a full-blown fire hours later, often after the shop has been shut down and no one is there to respond. For this reason, my most important recommendation is to empty the collected dust every day or at least keep it in a closed metal container.

Rod Cole is a woodworker and mathematician who lives in Lexington,


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## wstokes

Thanks for all the feedback. I especially appreciated Gary's long copy/paste. I'm strongly leaning towards not grounding the inside, even with metal tape (which would be quite difficult to pull through I imagine), but I most certainly will wrap the outside of the entire system with exposed metal wire and hook it up to all the tools and dust collector to ensure they are all in the same ground plane.


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## 33706

Oh ohhhhh…. that container of acetone just fell over….no problem, it's getting sucked up into the dust-collection ducts….ka-boom!! Nahhh….never happen.
Remember too, that MIT designed the John Hancock Tower in Boston, which dislodged giant panels of plate glass from as high as 68 stories, to the street below, whenever it got a little windy out. 
Sorry to disagree. Dust collection is one of the single most potentially dangerous things in the woodshop, other than procedures involving humans operating machinery.


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## cliffton

I have no idea about how grounding a DC works and have no opinion on it. My reply is directed to Poopiekat. The John Hancock Tower was designed by I.M Pei and Henry Cobb of Pei, Cobb Freed and Partners based in New York. Pei went to MIT and Henry Cobb went to Harvard. MIT was called in to research and figure out why the panels were falling out of the building. Their Wright Brothers wind tunnel was used for this. Please don't disparage the name of a great institution that without their help the problem wouldn't have been solved.

And now you know

This has been a public service announcement


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## Abbott

I've been using 4" PVC for years without any issues. At the moment I am running a one-horse unit until I get my old two-horse unit installed in the new shop. I have a straight 25-foot run with blast gates and 4 machines with good dust collection and no static electricity noticed.


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## 33706

Clifton: Ooooohh behold wickipedia! Thank you for pointing out that two men educated at prestigious New England universities could neither forsee an obvious construction flaw, nor resolve it on their own once the error became known. My point was, and is, why should we accept the static-control opinion of an educated mathematician based on HIS education? Are combustion flash-points part of math curriculum these days? Do experienced firefighters sit around the firehouse and discuss the Pythagorean Theorum with their buddies? Easy.


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## TheDane

Gary is right … the danger of fire from an ungrounded dust collector in an everage workshop is probably very low. Nonetheless, I ground mine … both the dust collector and the shop vac.

Reason? I have a number of electronic devices in my shop (notebook computer, CD player, and a couple of iSocket siwitches). Electrostatic discharge … even the small shocks you get off an ungrounded dust collector … is anathema to those devices, especillay this time of year when it is so cold and dry where I live. That little spark can damage the type of semiconductors used in these devices and can be costly to repair or replace.


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## JJohnston

No one has mentioned this yet, but don't glue your ducts! You'll never be able to get them apart if you should ever want to change anything. Put a couple of self-drilling sheet metal screws through each fitting and into the pipe. Normally, this is even a good enough air seal, but if you want better, wrap the connection with some foil HVAC tape.


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## cliffton

Poopiekat, yes wiki did help fill in the blanks but being familiar with MIT I had a few details on the history already.

The actual construction flaw was neither obvious nor simple it turned out that the bonding agent used to attach the inside and outside glass panels together wasn't pliable enough and was transmitting too much vibration to the outer panels.

I'm not sure why firefighters would be discussing how to figure out lengths of legs of triangles but I would guess that if they were trying to figure how far from the building they could park a ladder truck and still have the ladder reach the roof I suppose that Pythagoras would apply.

If education has no bearing on validity of a hypothesis then all "dem smart peoples" that aspired to higher learning apparently have been ripped off.


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## rareddy

Papadan,

You can't ground "airflow" either, since air is not a conductive material (well, except at a million volts when lightning strikes). It would be akin to laying bare copper on your carpeting with the goal of eliminating static build up when you walk across it. This really is just basic science here. As far as mfg instructions… well, manual writers are writers… nuff said.


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## dbhost

I'm running ungrounded, and not concerned at all about DC explosions.

If I had to take odds on what is more likely to happen, I need to protect myself from parts or debris from an airplane crashing through my roof and killing me. That is FAR more likely to happen. At least you hear about those things happening…

On the issue of glue, or not. I do not glue my ducts per se… I run a bead of clear adhesive silicone on the outside of the joint, so that a utility knife can quickly, and easily break the bond. and the joint will come apart for repair, or rearranging…


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## PCM

I currently have a 550 cfm delta two stage dust collector. I hook it up directly to each machine via a flexible 4 inch tubing. I was getting static shocks until I ran a copper ground wire through the tubing and grounded it to the dust collector. I no longer have any issues with static electric shocks. I can not vouche for the physics of this, but the results are clear.


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## exelectrician

I was getting shocks off my dustright hose which is a plastic expandable hose with a spring molded inside. I grounded the metal to my DC and, no more shocks.


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## SJThrasher

Thanks everyone for these great comments. I am getting ready to run some ducting in my garage and my fears have been for naught. I will run my PVC confidently and if I start getting shocked every time I touch something I will address that issue.


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## Gshepherd

So if I ground the hose wire to the DC I will not be getting shocked any more???? I have 2 of the Jet 1100cfm I use for portable collection cause I can't bear to watch the meter run when I crank up the 20hp Murphy when I am just doing the hobby stuff….


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## dozer57

grounding is for static build up, this causes dust to cling to pvc pipes. kind of like rubbing a balloon on your hair and sticking it on something. wood dust causes static and collects and hence poor air flow and eventually plugging of pipes will happen. I have wrapped mine in bare copper with short screws at every connection that sticks thru about 1/8 in. and no more build up in pvc. imo worth the time


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## bigblockyeti

I worked in a millwork shop during college and we had a European 10hp DC with 10" green PVC run as the main trunk line. Running a lot of fine dust through it for an extended period of time would result in quite a buildup. To the point that it could zap you in some cases from over 6" away; Not very comfortable.


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## Gshepherd

> I worked in a millwork shop during college and we had a European 10hp DC with 10" green PVC run as the main trunk line. Running a lot of fine dust through it for an extended period of time would result in quite a buildup. To the point that it could zap you in some cases from over 6" away; Not very comfortable.
> 
> - bigblockyeti


Dont tell me that…... Mine is hooked up to the moulder and SLR saw. it pulls 7200cfm. I just put a groud wire on my little Jets and grounded the hose wire and tried it and no more shocks…. I feel like a new man now….. Sad it took me so long to correct that problem…


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## intelligen

Bob Areddy has it right. If anything, the charged air particles flowing through the pipe will repel one another outward toward the walls of the pipe. If PVC were a conductor, you could then ground the inside or outside of the pipe and be done with it. But PVC is an insulator, so that won't work. Just as the charge cannot pass from the inside to the outside, it also cannot pass along the inner or outer surface of the pipe. The charge remains localized, and discharging it (e.g., grounding or getting a static shock by touching it) at one location will not dissipate the charge along the length of the pipe.

Even if you run a wire along the length of pipe on the inside, at best the localized parts of the pipe that are touching the wire will be grounded, but most of the pipe will remain charged. If you run the wire through the very center of the the pipe so it isn't directly touching any walls, you'll only collect the charge from the immediate air passing over the wire. It is only once the walls are charged that they will be able to repel excess charge toward the perfectly-centered, uncharged ground wire-in which case, your attempt to prevent the build-up of charge on the walls has already failed, but perhaps the charge that builds up on the walls is not as high as you would otherwise have. Another possibility is that the only reason grounding seems to help against static shock is that the ground wire repeatedly draws high-voltage static discharges (static shocks) from the walls of the pipe. In either case, you're not preventing static discharges; you're only putting a cap on the voltage of each discharge.

If you're really set on grounding the PVC with the goal of preventing static discharges, the only thing that makes sense is to coat the inner surface with a conductive material (such as aluminum foil tape) and ground that, as Dez mentioned.

Someone also mentioned using dryer vent instead of PVC. The downside is that you have to buy thicker duct than what is normally used to vent a dryer, because the small gauge duct will implode.

Will, as far as your overall plan for a dust collection system, be sure to look at the CFM curves for static pressure drop for your particular dust collector, and factor in the diameter and length of the pipe, as well as any bends. The more modern literature on the subject boils down to needing a certain CFM at the tool to overcome the speed at which small particles are discharged in the opposite direction by the spinning blade. Calculate how fast the cutting edge of the blade is spinning, and make sure your dust collector is pulling air in the opposite direction faster than that.

Even if you do manage to capture all the dust, you'll need HEPA-level sub-micron filtration to make the air safe to breathe-that means better than what you'll get from any bag filter and most canister filters. Simply put, the only practical purpose of all but the most high-end dust collection systems is to help keep your tools running cool by providing airflow and removing dust and chips. You'll still need to wear a respirator while you operate your machinery and afterward until most of the dust has had a chance to settle, which will be at least a half an hour later if you don't have any fans running.


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## Pezking7p

You do not need to ground the pipes, only the metal parts and the ends of the tubes where dust is discharged or sucked in. Btw, metal parts should truly be grounded, or alternatively bonded to ground by connecting the metal electrically to something which is grounded.

Explosions happen when there is enough electrical potential between to components to cause a spark, typically at least 20kV/in. Therefore you want all your metal parts to be bonded, that way the beginning and end of each run is at the same electrical potential.

Putting wire inside you pipes will not do much except clog up your pipes. The wires will almost immediately become coated with dust and at that point they won't discharge any static and they become useless. The same is true of putting wire on the outside of the pipe, since it is electrically separated from the dust/air by the pipe.

Bond your metal fittings/ parts to each other and to ground , and you'll be all set.


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## intelligen

Ha! Nevermind, I think we're all demonizing static shocks when we should be using them to heal ourselves.






Remove your grounding and start healing your headaches and minor aches & pains!


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## BillWhite

Into the fray my soldiers! Into the fray. Bullets alone won't win the battle. Into the fray!
BTW, that was an original. (

I found that putting a dryer sheet (as in clothes dryer) thru the ducting and into the collector puts an end to any static in my DC. Stupid simple, and very inexpensive.

Wanna come to my shop to see the system? If so, you would only have to let me know when you're comin'. 

Bill


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## runswithscissors

If I ground my system, and never have an explosion, doesn't that prove it works? Same reason I keep a sign over my door that says, "Keep this house safe from tigers." And guess what? I have never been troubled by tigers!!


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## wstokes

I'm not sure why my question for ages ago is suddenly generating so much attention. I guess one reply kicked it onto the home page? Regardless, in case any one is curious i ended up wrapping the outside of my system and it stopped the small shocks I get before I took that step. I don't seem to be having issues with clogs in my lines and opted against running wire within the pipe because I decided that would ultimately make matters worse. Some day if I were to do it all over again I would use metal but that's pretty expensive, hence I went the PVC route this time around.


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## TopamaxSurvivor

When I wired gas pumps in the early 70s, I saw quite a few fires under them. Never saw one blow up. Does that prove fires under gas pumps are not risky business?


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## TopamaxSurvivor

Did you totally wrap it or just wrap a grounding wire around it?


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## wstokes

I spiraled a grounding wire around the entire thing and attached the ends to metal on each piece of equipment as well as the dust collector.


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## robscastle

Have a read of my blog regarding the grounding of my home made unit.

Wood dust/shavings separator


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## Bill7255

Reading through this there are some that ground and some that don't who use PVC. Good news is no one has experienced any problem either way. Then for those that ground PVC there seems to be differences whether to put the wire inside or wrap the pipe. The one thing that seems to be consistent is if using metal you should ground. So I have decided to run metal and ground it to the DC. This way I don't need to worry about grounding PVC.


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## doitforfun

Interesting topic. I don't have anything to add scientifically, but I have done anecdotal experience. I built a small cyclone using a paint bucket and an orange cone for my shop vac. Normally it sits on a 5 gallon bucket. I also made an adapter so that it fits on a 50 gallon barrel for those days I'm using the planer and making way more shavings than a 5 gallon bucket can store. The only time I have ever noticed static electricity is when it's on the barrel. So it seems that volume alone has a large impact on the amount of static charge.


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## TopamaxSurvivor

> The one thing that seems to be consistent is if using metal you should ground. So I have decided to run metal and ground it to the DC. This way I don t need to worry about grounding PVC.
> 
> - Bill7255


All metallic systems in any building is required to be grounded by the National Electric Code for safety reasons. No static shocks are just a side benefit ;-) Cheers, Bob


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## groygroy

papdan

RE: "Andy, If I ever have reason to redo my DC system, I will use metal duct pipe for it. Anyone using thiers as a portable and hooking it up to one machine at a time does not need to ground it. Thier hose would only be a few feet long and not have enough action to build up a charge."

Note, I don't have PVC piping in my system.

You do need to ground the protable p2p hookup if you put both your collector and your separator can on plastic wheels (like I stupidly did). I have the 4 inch flex pipe WITH a grounding wire embedded in it. My separator is a galvanized steel can. Everything worked great until I put that can on wheels. As soon as I put that can on plastic wheels I started getting shocked frequently during use. To solve this I twisted one end of a copper wire around the handle of the separator can, twisted a sizeable hex nut onto the other end, then dropped the nut on the concrete floor. No more shocks!


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## groygroy

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