Grounding Wire for Dust Collector

[tri4sale]

I'm redoing my dust collection system, and running some PVC pipe for the dust collector hose system. When running the grounding wire, should I run it inside the pipe, or outside the pipe. On my old layout using DC hoses I did run it inside the hose, but just wondering if it would still work when run on the outside of the hose/pipes (which is easier to run).

[pro70z28]

You'll get both answers on this subject. I ran the wire on the outside with a self tapping screw through the pipe every 16'' to 2'. On my new system I screwed conduit to the pipe and that ground has proven to be just as effective. I didn't like the wire inside because I thought it would collect the stringy wood fibers I got from cutting with the grain. Since the newer software, 3-D capable, the stringy wood deal doesn't occur as much so that may not be a valid theory anymore. I can say though, I had bad static problems before grounding and have had no static problems since the ground wire, going on 20+ years now. So, my advise is not so much WHERE the wire goes as much as that you HAVE a ground wire, properly grounded, of course.

[coryatjohn]

I would suggest not using PVC for dust collection ducting. Use metal ducts or hoses specifically made for dust collection instead. If you have a high volume of dust and the air is dry, you're setting yourself up for a potential explosion. I suppose the risk of that is not huge but it's a risk still. In my opinion, no amount of grounding is going to be 100% effective with PVC.

[dlcw]

Running wire inside a CNC dust collection pipe can cause some problems. If you cut a lot of plywood, you get "strings" of plywood as it gets milled and cut. These "strings get hung up on the wire and cause the pipe to clog. I do use flex hose on my CNC dust collection setup. It is the wire wound stuff so I can use that wire to provide for my grounding system. I woulnd't use a non-wire wrapped flex piping. PVC is OK, but like cortatjohn suggested, use metal instead.

[jTr]

The most respected resources on this forum have always advocated for locating ground wire inside, be it a short run of flex line from machine to a main metal duct branch, or a complete pvc system.

Reason: the dust chips are causing static rubbing along inside of any plastic duct, be it flex hose or pvc.
Discharge of that friction energy should be taking place inside as well, in order to shunt any charge as it is being generated.

When placed on the outside, internal static may not be discharged until it reaches ground at the pickup, very close to your machine, which is where you don't want it. Better to discharge inside the tube than let it build to that entry point.

You may be successfully avoiding comm errors with continuous external ground, but you are not fully mitigating risk of fire, IMHO.

Yes, stringy fibers can catch on that wire. My clear flex tube does so periodically, but I am able to see if a clog is developing and take care of it. Indeed, with pvc, you cannot visually detect this problem.

Optimal solution: Use professional grade spiral metal duct work, and you won't need to run a ground wire inside OR outside, as long as you are grounded at the collector. Further, if you are running a professional shop and your insurance company sees it, you'll likely be asked to remove / replace the pvc or risk non-renewal of your policy.

Exceptions:
1>
no static problems since the ground wire, going on 20+ years now.

Okay, hard to argue with that for comm issues, but what of the ever-present risk of fire? Neutralization of static with an internal ground wire is again, one step closer to safety, especially with wood chips and dust.
If I recall correctly, you are milling aluminum more than wood, so your exposure is a bit unusual compared to majority of users running primarily wood chips through those lines.

2>Perhaps your insurance carrier hasn't had any major losses with your type of business category in your region and doesn't feel compelled to inspect. Would hate to be in an argument with the adjuster about an unapproved (or worse, excluded from coverage) method of dust collection after a loss.
Just because they haven't discussed it with you, doesn't mean they're cool with it.

I hate taking dictation from government and insurance companies, but thanks to my insuror's inspection and correction of my finish room practices and electrical systems years ago, I function much more safely, and therefore sleep and breathe better. Never did have a problem prior to their advice,
but it doesn't mean I was not at risk.

At the end of the day, the argument for internal grounding of flex lines connected to spiral metal duct wins for me.

Safety First !

Jeff

[pro70z28]

If I recall correctly, you are milling aluminum more than wood, so your exposure is a bit unusual compared to majority of users running primarily wood chips through those lines.

Not sure where you got that. The few times I have, I don't run the VAC at all as I don't want metal chips and oily coolant sucked thorough the VAC system.

[garyr6]

Thanks for your input. You remind me that at times I cut corners on safety, thinking "oh it will be ok this time, or its not going to happen to me."
So if you're going to do it do it right. I certainly did, "after my fire".