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Thread: Grounding dust collection system for static build up?

  1. #1

    Grounding dust collection system for static build up?

    I would like to make sure my newly installed dust collection setup is grounded to prevent static build up. I'm not concerned about the possibility of fires in the ductwork but the annoying shock that might occur. All of the ducts are metal with flexible hose at the machine connections. Is it necessary to maintain continuity from the metal duct to the machine through the steel reinforcement in the hose? If so, does that also apply to the flexible hose at the dust bin? And finally, should there be a grounding rod or connection to ground made for the system?

  2. #2
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    Quote Originally Posted by Steve Mathews View Post
    I would like to make sure my newly installed dust collection setup is grounded to prevent static build up. I'm not concerned about the possibility of fires in the ductwork but the annoying shock that might occur. All of the ducts are metal with flexible hose at the machine connections. Is it necessary to maintain continuity from the metal duct to the machine through the steel reinforcement in the hose? If so, does that also apply to the flexible hose at the dust bin? And finally, should there be a grounding rod or connection to ground made for the system?
    Any ungrounded metal in a duct carrying dust can be both a shock and arc hazard. That includes the spring wire in a flexible hose. You can ground either end or do both for some redundancy.

    Ideally you use the ground bus in you shop subpanel for the ground connection. A separate ground rod that is not properly connected to the electrical grounding system is a safety issue and should be avoided.

    You can't prevent the buildup of static charge on the inside of an insulating hose. You can, however, wrap it in an equal and opposite charge. This shields you from the charge on the inside by essentially shorting out it's electric field. Grounding the hose wire provides exactly the right amount of charge in the wire to balance the charge inside the hose, like one plate of a capacitor.

    Grounding the hose wire is needed at the dust bin too. That's someplace you probably don't want arcing, even on the outside.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

  3. #3
    Quote Originally Posted by David L Morse View Post
    ...
    Ideally you use the ground bus in you shop subpanel for the ground connection. A separate ground rod that is not properly connected to the electrical grounding system is a safety issue and should be avoided...
    Why is it a safety issue to have a separate ground rod? Also, isn't a ground back to the subpanel ground bus made when there is continuity back to the machine, which is probably grounded to that bus?

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    Quote Originally Posted by Steve Mathews View Post
    Why is it a safety issue to have a separate ground rod?
    A rod in the ground that does not have a metallic connection to your building's grounding system has nothing to guarantee that it's not at a significantly different voltage.

    Also, isn't a ground back to the subpanel ground bus made when there is continuity back to the machine, which is probably grounded to that bus?
    Sure, that's the way it's often done. I said "ideally" because a machine can be unplugged and you then lose the ground connection. I often don't do what's ideal myself. IIRC, code actually requires a #8 wire to the ground bus for proper grounding of infrastructure. I'm not sure if that applies to dust collection duct though. There are code requirements about grounding dust collectors but I'm not familiar with them.
    Beranek's Law:

    It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
    L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.

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    I can only speak as to what has worked for me for over 15 years. I run ASTM-2729 PVC so my static buildup potential is pretty good. I attached an insulated stranded wire to the electrical ground of my shop plant and wound it about 1 turn per foot from end to end.

    pvc-response-002.jpg

    At the end of an awkward long run I stuck foil tape to a scrubbed section of slab and clipped to it; works great.

    G0440-ground-004.jpg

    I do use the metal helix in the hose from gate to machine, for quick disconnect locations I manage this with an alligator clip (bottom of pic).

    duct examples (2).jpg

    When the hose is not in use the clip just rests on the pipe.

    blast gate anti clog (2).jpg

    I don't bother connecting at the machine end. As long as there is a better route to ground than through you, your shock problem goes away. The grounded wire allows very easy incremental discharges along its path as buildup occurs. Your metal ducting will make this even easier but, the same principle applies.
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

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    Quote Originally Posted by Steve Mathews View Post
    I would like to make sure my newly installed dust collection setup is grounded to prevent static build up. I'm not concerned about the possibility of fires in the ductwork but the annoying shock that might occur. All of the ducts are metal with flexible hose at the machine connections. Is it necessary to maintain continuity from the metal duct to the machine through the steel reinforcement in the hose? If so, does that also apply to the flexible hose at the dust bin? And finally, should there be a grounding rod or connection to ground made for the system?
    No it isn't necessary if the machine is also grounded.

    I grounded the duct end of the flex hose spiral wire to the duct, which is grounded by the metal cyclone body through the power grounding........Rod.

  7. #7
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    The best way is to use stranded copper wire, uninsulated. Connect to an unpainted bolt on your dust collector (that is connected with a three prong cord and grounded outlet). Then connect to metal duct or drill into plastic duct with a small hole to insert a screw that protrudes into the duct about 1/4 to 3/8 inch. Install a screw every few feet. This is where the fire hazard arcing is. Wrap the wire around these screws and tighten. For long runs it’s best to ground on both ends.

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    Here is how I grounded one of my flex hoses:
    Attached Images Attached Images
    NOW you tell me...

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    I very much doubt that tape is electrically connected to ground. Most adhesives are insulators as is dry masonry.
    Bill D

  10. #10
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    I wrap copper wire around aluminum rivets and rivet the wire every 2-3 feet from beginning to end at the machine. The rivets act as probes inside the pvc pipe.
    Ask a woodworker to "make your bed" and he/she makes a bed.

  11. #11
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    Quote Originally Posted by Gordon Stump View Post
    I wrap copper wire around aluminum rivets and rivet the wire every 2-3 feet from beginning to end at the machine. The rivets act as probes inside the pvc pipe.
    The OP has metal ductwork...........Rod.

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    Quote Originally Posted by Rod Sheridan View Post
    The OP has metal ductwork...........Rod.

    I know but Bruce King mentioned screws in plastic pipe so I added my $.02 Always want to talk about my favorite subject.....me!
    Ask a woodworker to "make your bed" and he/she makes a bed.

  13. #13
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    Don't drive yourself nuts here. All you want is a "drain" wire.

    Quote Originally Posted by Steve Mathews View Post
    I would like to make sure my newly installed dust collection setup is grounded to prevent static build up. I'm not concerned about the possibility of fires in the ductwork but the annoying shock that might occur.
    All of the ducts are metal with flexible hose at the machine connections. Is it necessary to maintain continuity from the metal duct to the machine through the steel reinforcement in the hose?

    No. You are trying to mitigate static buildup, not establish an equipotential plane.

    If so, does that also apply to the flexible hose at the dust bin?
    Not really, see above.

    And finally, should there be a grounding rod or connection to ground made for the system?
    No. Tie the ground/drain wire to your dust collector frame. The frame of your dust collector, and all of your machines, are at ground potential.
    Driving a second ground rod creates the ability to have two ground references, through the dust collection system, and the machines. You could possibly introduce circulating ground current, or have your ground reference change. The grounding scheme for your building should be sufficient

    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  14. #14
    My last shop had 4 inch S&D PVC piping for the DC and collected a lot of dust on it due to static, I guess. I probably needed a grounded wire on the outside of the pipe. My current shop has 5 inch metal snap lock pipe and I haven't noticed any dust buildup. It is not grounded. It connects to my super dust deputy which is plastic so there is no path for it to be current carrying but it could build up static but doesn't seem to. I have never been zapped moving a metal blast gate. If I notice an issue. I will run a ground wire to the duct and connect it at an outlet. Steel is not a great conductor but it is plenty good enough that I will not need a wire along the length of the duct. I do not worry about flex. I've never been zapped by it and it moves enough in use to shake off any dust.

    There is no explosion risk from dust in a woodshop. You need to ground if you are getting zapped or you don't like apparent dust buildup. At least that is what all my research indicates. Dust that can burn can be explosive but only at exactly the right dust to air ratio which is very high. It will not occur in an environment you want to be in.

  15. #15
    I'm having a hard time wrapping my head around this one. But based on the comments above and some additional research online it seems that I'm in fairly good shape with dissipating static buildup in the ductwork by having metal duct riveted together, which is attached to the Oneida all metal dust collector. The DC is properly grounded at its electrical connection. There may be some additional grounding at the floor sweep where it makes contact with the concrete floor borrowing from Glenn's installation. Then again, maybe that is a concern based on Mike's comment about having an alternate path to ground. The only change I plan to make for now is connecting one end of the flexible hose wire reinforcement to the metal duct. I'll leave the other end attached to the machines alone as the machines are already grounded. I'll also connect both ends of the flexible hose wire reinforcement to the DC and dust bin. That should take care of static buildup caused by movement of air and sawdust in the ductwork but there is static buildup created elsewhere that is probably more to my original concern. Last night I was buffing a wood bowl on my lathe and the shocks I got were constant and predictable. It only took a few passes on the bowl to generate a good shock. Our humidity is usually quite low in the high desert of Northern Arizona and I'm sure that contributes to the problem. I recall having similar issues when using the belt sander and even the jointer. Here is where I'm at a complete loss as to what to do. The static buildup is obviously caused by the buffing, grinding, etc. and the electrical imbalance is between the item being worked on and me. So, what to do? Clip a wire to my nose and a source of ground?

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