DC ducts - 4" or 6"

To begin with, the wire goes on the inside, and is connected to all equipment and earth ground. And I believe the intention is to reduce potentials across varying sections of pipe and the metal equipment. As anyone familiar with science fair projects can attest, easily generated static charges can be on the order of 20,000 - 80,000 volts.

Again, I didn't design it, recommend it, or sell it. I am only reporting what is required by our commercial fire code.

Greg G.

Reply to
Greg G.
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Should the ground go though a resistor to limit current?

-- Mark

Reply to
Mark Jerde

No, there is no current to speak of - it never has the opportunity to build up any potential as it is constantly leaked away to earth ground. It probably wouldn't hurt anything either, just more crap to possibly fail.

Greg G.

Reply to
Greg G.

Howard-

before you go any further, read this:

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Bridger

Reply to
nospam

I believe that is what you think you are doing. But, for example, statements like:

can lead to confusion. It sounds like you are saying that some fire codes require commercial installations of PVC ductwork to be grounded.

AFAIK, fire codes that require grounded ductwork in commercial installations also require the ductwork itself to be metal (or at the very least, conductive). I have never heard of, and seriously doubt the existence of any code that requires non-conductive ductwork to be grounded. It just doesn't make any sense because it is impossible to "ground" an insulator.

Jim

Reply to
Jim Wilson

from

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inside wire or grounded screws: Many people use a bare grounded wire inside the ducts. This may provide some amount of leakage current, but the primary effect is to provide a shorter hop to ground than if no wire is added. Since the wire has a very small radius, the field due the charge drawn into it by the static charge is large, making discharge occur at smaller charge densities than if the wire was not there. The discharge will be a brush type discharge which will not ignite the dust. This limits the amount of charge that can build up, which in turn limits the strength of the field outside the pipe where your unsuspecting finger is. Basically, this reduces the chance that your finger will become the shortest path to ground! By limiting the charge build up, this also reduces the chance of a propagating brush discharge. Grounded screws poking through the duct wall provide much the same protection. For a single wire in a 4 inch duct, the maximum discharge distance is 4 inches. The maximum discharge distance for screws placed 4 inches apart along the pipe is 4 inches across the pipe and 2 inches sideways, for a total distance of just under 4.5 inches, so the protection is about the same, and may even be better as screws have sharp points that increase the strength of the electric field leading to discharges at smaller charge densities. Because this type of grounding does not have the potential to cause a propagating brush discharge, I think this is safer than the external ground wire. Using very short screws will not cause the jamming up of shavings that often occurs with the internal ground wire.

Reply to
nospam

Not necessarily doubting you, but can you point to more proof? Whenever I put a strap on my wrist to solder electronic components the ground had a large resistor in it. I confess to the (possibly irrational) fear of having a basically unlimited Columb/Sec path to ground in my shop.

-- Mark

Reply to
Mark Jerde

Yes, metal is *supposed* to be used in commercial installs.

But it IS possible to reduce and dissipate accumulated charges in PCV through surface leakage so that large discharges to metal objects is all but eliminated. Of course you can't "ground" PVC in the classic sense, it is an insulator. But in reality, all materials conduct electricity to some extent, especially in high humidity conditions, their resistance is just *extremely* high.

Well anyway, this thread is getting quite tedious. WAY too much grief over installing $3 worth of wire. Especially considering that the negative consequences of doing so are nil. Too bad people aren't more interested in the direction our economy or world politics is headed.

Folks, do what you want, believe what you want.

I'll stick to my conductive, impregnated plastic pipe and enjoy the peace of mind of knowing that when I brush against a pipe, I'm not going to get zapped by static discharge - which is my primary concern.

And maybe, somewhere deep down inside, I may even get some comfort in knowing that I may also avoid that 1 in 1,000,000 chance that my DC is going to catch fire. The universe is a cruel and chaotic place.

Happy Holidays!

Greg G.

Reply to
Greg G.

I have done electronic work for 35 years. How do you like soldering in those 82 pin SMDs?

I believe the resistor in the strap (or the impregnated, high resistance strap itself) is to protect you in case you contact live wiring, not to protect against unlimited amounts of static charge. It also lessens the discomfort of discharging any static buildup in your body from shuffling across the carpet. I don't use them myself, as I simply discharge myself to the equipment and ground before working and don't squirm about while I work. Never had a failure. I have a friend, however, that we like to call Mr. Lightning. He can *look* at a PC board and it zaps. I keep telling him it's his cheap shoes, but I don't think he believes me.

As to the unlimited path to ground, all of your equipment is grounded, do you fear it as well?

I can't give you any PHD references on this one, sorry. And I'm to tired to Search one out.

Greg G.

Reply to
Greg G.

Reply to
DAN & CINDY

Keeter, you forgot to tell me you are from MO.

Only believe what you see with your own eyes? Never learned anything by reading or listening to others? A fair amount of skepticism is fine, but you pretty much are calling folks liars when you refer to someone as a "myth teller".

Now I've given you reason to get back to busting my chops... :)

dave

Unisaw A100 wrote:

Reply to
Bay Area Dave

Does this mean I get a gold star?

Greg G.

Reply to
Greg G.

even metal will burn if atomized sufficiently.

dave

Greg wrote:

Reply to
Bay Area Dave

just for the record; we aren't all as skeptical is Unisaw100... I'm with you, D&C.

dave

DAN & C> For all you disbelievers that dust cant explode I've had the unfotunate

Reply to
Bay Area Dave

Yep, and those magnesium plane parts, hmm...

Personally, I like to throw various metal powders into the fireplace to see the pretty colors... SWMBO likes it too.

Greg G.

Reply to
Greg G.

Aw, don't mind him. He's just a crusty old fart sparrin' for a fight. Probably didn't get any this weekend...

Greg G.

Reply to
Greg G.
5" would be a real pain..

would have to find pipe.. no s&d.. prolly some metal somewhere

then i either have to make all new ports.. or do 5" to 4" conversions..

5" really does not seem practical.

if 6" is going to be a velocity issue.. then i will go w/ 4"

the ts, jointer, planer, and bs are all w/i 12' of the DC to the north-east

the scms is about 12' also.. but due north

the dp is about 20' due north

it's looking like i have collection needs in the lower left and upper left quadrants of the shop.. and no needs in either right quadrant

the DC sits in the lower left of the 18w x 23h shop

how come none of the trade mags talk about 6" ducting?

Reply to
nospam_coloradotrout

Reply to
Bay Area Dave

no star. to paraphrase the quoted link... attempting to ground plastic dust collection pipe is a waste of time. 'cause, it ain't gonna 'esplode no how no way. wrapping wire around the outside actually increases the discharge energy inside the pipe or some such, but it's still several orders of magnitude too little energy to 'esplode. putting wires inside the pipe causes the sawdust and shavings to hang up and clogs the system.

Reply to
nospam

Your pretty broad interpretation, perhaps. My technical information was pretty much in line with what you posted from your "mywebpage" source - I didn't bother to read the link. And who made this guy the God of DC's, anyway?

It didn't say that. It said the probability was minute.

I never said anything about wrapping wire on the outside of pipe.

I don't see any mention of that in that paragraph... And properly done, not very likely.

And you totally dismiss the static discharge issue. I personally don't like to get zapped by PCV pipe discharge, nor do I like to see clods of sawdust hanging from the ducts due to static buildup. These factors alone are worth the $3 - to ME.

I won't bother to disseminate any more, it ain't worth the effort. Two people can read one man's opinion, and come up with two more of their own. Ain't this country great?!

Opinions are just that - we'll have to just agree to disagree.

Greg G.

Reply to
Greg G.

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