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Grounding your Dust Collection System

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Forum topic by Will Stokes posted 1622 days ago 20731 views 0 times favorited 26 replies Add to Favorites Watch
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Will Stokes

261 posts in 1939 days


1622 days ago

Topic tags/keywords: dust collection grounding pvc wire spark fire question

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?


26 replies so far

View papadan's profile

papadan

1107 posts in 1953 days


#1 posted 1622 days ago

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.

-- Carpenter assembles with hands, Designer builds with brains, Artist creates with heart!

View SteveM's profile

SteveM

108 posts in 2752 days


#2 posted 1622 days ago

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.

View poopiekat's profile

poopiekat

3527 posts in 2319 days


#3 posted 1622 days ago

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!

-- Einstein: "The intuitive mind is a sacred gift, and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift." I'm Poopiekat!!

View Bob Areddy's profile

Bob Areddy

177 posts in 1987 days


#4 posted 1622 days ago

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.

-- --Bob http://www.areddy.net/wood

View Bob Areddy's profile

Bob Areddy

177 posts in 1987 days


#5 posted 1622 days ago

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

-- --Bob http://www.areddy.net/wood

View TopamaxSurvivor's profile

TopamaxSurvivor

14550 posts in 2260 days


#6 posted 1622 days ago

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

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View pvwoodcrafts's profile

pvwoodcrafts

222 posts in 2506 days


#7 posted 1622 days ago

Oh geez, not here too!!!

-- mike & judy western md. www. pvwoodcrafts.com pvwccf1@verizon.net

View papadan's profile

papadan

1107 posts in 1953 days


#8 posted 1622 days ago

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.

-- Carpenter assembles with hands, Designer builds with brains, Artist creates with heart!

View papadan's profile

papadan

1107 posts in 1953 days


#9 posted 1622 days ago

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.

-- Carpenter assembles with hands, Designer builds with brains, Artist creates with heart!

View TopamaxSurvivor's profile

TopamaxSurvivor

14550 posts in 2260 days


#10 posted 1622 days ago

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.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Amac's profile

Amac

4 posts in 1626 days


#11 posted 1622 days ago

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.

-- Andy

View Dez's profile

Dez

1113 posts in 2662 days


#12 posted 1622 days ago

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.

-- Folly ever comes cloaked in opportunity!

View papadan's profile

papadan

1107 posts in 1953 days


#13 posted 1622 days ago

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.

-- Carpenter assembles with hands, Designer builds with brains, Artist creates with heart!

View GaryK's profile

GaryK

10262 posts in 2573 days


#14 posted 1622 days ago

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,

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View Will Stokes's profile

Will Stokes

261 posts in 1939 days


#15 posted 1621 days ago

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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