How crucial is it to ground your DC system?

[big tim]

Sarge, your shop makes me want to bawl like a baby with a messy diaper................

I'd like to see that,
On second thought, maybe not!

Tim

[SARGE..g-47]

Well guys, this is getting to be an interesting read.... I have read Bill Pentz's site several times and quite a few more on this subject. Every one I read seems to have a different take on what will.. what won't and even as Tom stated... just ain't gonna happen as Bill Pentz seems to agree even though he did mention a gentleman in a commercial enviroment that wrapped the the outside and inside before assembly with aluminum foiled tape.

Bill Pentz praised that move as he said it worked after just having stated that probably nothing would work as Tom stated. Huh... say what, Bill??

Yep.. pretty confusing as everybody has a different out-look. I expect this in an electrical wiring conversation as I have seen EE's involved, certified electricians and every one dig in with a stand and not budge. An agreement seems to never be unanimous:>)

I'm at a point that I need to make a decision to wire or not to wire my PVC. I noticed a pattern in what has been said so far. Tom in Mn. gets zapped and he says probably nothing will work.. Lee in Oh. was getting zapped and ran a ground wire and no more zap. GS has heard of someone that drove sheet metal screws through with sucess. GS is in Mo.

Everyone that said they got zapped has been in a colder climate. It is said that cold and dry promotes the level of static in PVC even though it is definitely a non-conductive as Tom stated and that's means it will pick up static.

So... I am very curious at this point. I may not do anything and see if I get zapped. If I do I will then just wrap the outside of the PVC and ground it to the self ground in the clear 6" flex pipe I am using at both the inlet and the final 10" to my machines to see what happens. If that doesn't work, I may drill 1/8" pilot holes and screw in #8 sheet metal screws. Then attach the outer wrap at about 1/4" of it's head I leave proud. And if all else fails I might go back and try foiled tape inside and out as I only have about 10' of PVC over-head.

If that fails.. I'm gonna tear the whole thing down and put a 10' lenght of flex hose up to replace it... which is what I probably should have done in the first d*mn place.

Regards... ha.. ha... ha..ha..ha..

[LCHIEN]

Electrical engineer chimes in

Static electricity is interesting stuff.
The problems it causes are anyehere from igniting explosives to creating electrical interference with and damaging electronics, to personal shock.

The home woodshop does not contain explosive concentrations of dust. Nor is there likely to be electronics related problems. The personal shock reaction is probably the biggest problem you should be concerned about.

It has some danger, due to reflexive reaction, it may (a) make you fall, maybe off a ladder or (b) come in contact with dangerous items (power wires or rotating/cutting machinery).

Some basic facts:
Anytime you have fast moving air you potentially risk building up static charges, the air strips away electrons. If the place where the electrons are stripped is insulated by a non-conductor a charge can build up. The charge is proportional to the size of the area and inversely proportional to the distance to ground (we're talking capacitor basics here).
If the voltage gets too high, it can jump an air gap to get to ground.
A grounded metal item can't build up static.


So, First and obvious, your DC should be grounded by virtue of the three prong plug - don't be stupid and defeat that (it also prevents electrocution due to power wire insulation failure). The tools should also be grounded in a similar fashion.

That only leaves the piping.
You can A) have metal piping which will not build up a charge if the metal piping is connected to the grounded chassis of the DC and tools.
B) use PVC piping which will have some charge buildup.
or C) have a plastic conductive pipe (this is not commercially available to my knowledge, but is the best sol'n and is quite within our ability to manufacture using some conductive additives in the plastic)

In the case of B, you can try and dissipate this charge or live with it.
Living with it means you will get shocked when you touch it and its running on a dry day. It will be a very mild shock and not dangerous on a reflexive basis because the non-conductive pipe will only discharge the charge from a very small area (a couple of square inches) due to the insulating properties of the pipe. Maybe uncomfortable but not strong enough to cause a bad reflexive reaction.

The worst thing you can do is to put a large conductive area on the inside of the pipe and another on the outside, with no grounding. Now you've built a perfect capacitor with a thin dielectric (the pipe wall) that can store a huge amount of electrons and deliver them to the point of discharge and you will get a whopper of a shock.

You can also try and put wires or mesh covering and screws through the wall and all that, and it all has to be grounded to the machines at the ends. But its probably not worth the efforts.

I say ground the machines at both ends and don't worry about the rest.

[JimD]

I stopped worrying about my PVC dust collector piping after reading an article entitled "PVC Pipe Dangers Debunked" in the Tools and Shops issue of FWW in 2001. The author, Rod Cole, cites sources like the "Journal of Electrostatics" to say that sparks outside a pvc pipe occur but are much less likely inside. In addition to the unlikely spark, you'd have to get just the right dust to air ratio for the dust to ignite. Another factor the article cites is the National Fire Protection Association puts no regulations on dust collection systems of 1,500 cfm or less (he says that is about 3 hp). The author suggests being careful about cutting through nails or sucking up metal since either could put hot metal into your wood dust creating a fire.

Jim

[SARGE..g-47]

Morning Jim...

I read the same article along with many others and I agree about that the explosion or fire hazard is very minimal in a small shop. But... PVC does create a bit of static electricity which can shock you.

I just installed a new PS cyclone and am faced with the shock from static electricity at this point. I haven't put an sizable stock through at this point that the cyclone runs but several moments. That won't come till next week-end as I start another large project.

So.. my question to you as you live in Lexington, S.C. (which is similar to Atlanta as warm and relatively dry) is if you haven't grounded your PVC, are you getting shocked? I am thinking of just not grounding it at this point to see if I can't get feed-back from local southerners just to see. If it does, gound it at that point in steps just to see what it takes to eliminate it or.. can it be eliminated period?

There seems to be no definitive answer to this quetion. Most of the shocks I have read about are coming from colder climates, even though that info is limited to forums and may not reveal more than a sampling of just how many are and how many aren't.

Feed-back would be appreciated and thanks in advance.

Regards...

[drumpriest]

To me, shock is definitely the problem to worry about. I have run a 1 1/2 hp DC through a 10' hose to a drum sander, and had it generate a pretty good shock. Certainly not the most pleasant of things.

[JimD]

Sarge,

My system is in an extra unconditioned garage in the basement. It is insulated but not deliberately heated or cooled (because it is surrounded by house it gets conditioned to some degree, however). My gates are wooden - plywood and hardwood scraps- and my tubing is plastic. No grounds. My DC is a 1 hp Delta with upgraded felt bags.

I have never gotten shocked by static from my DC. I am not sure why others have and I have not. I mentioned the gates and other details because I think it might make a difference. I rarely touch the piping or flexible hoses, I am almost always touching the wooden gates. I have to move the gate around every time I switch tools, however. The 1 hp DC works pretty well except for the INCA jointer/planner where it is a bit marginal. It doesn't work well for the other tools with multiple gates open, however. So I move gates a fair bit without shocks.

Jim