I'm new to the group and don't want to get roasted here, but I have a tale
to relate. Many moons ago I was cleaning out my shop after a long winter of
woodworking projects, I use my compressor to blow the dust that had
accumulated in the shop into the air then vacuumed up the dust that settled
on the floor. I repeated this a few times until my shop was as dust free as
the day I built it. It was not until later in the day that I learned the
power of dust explosions. I had taken all the shop scraps and what not out
to the burning barrel on the back of the property and was finishing up with
yard waste when I remembered that the Shopvac needed to be emptied and the
burning barrel seemed like a good repository for the contents. Now I will
give you that a 45 gallon drum filled about 3/4 full of embers has slightly
more energy than a static electricity spark, but the resulting 40 foot fire
ball was enough to instill in me a healthy respect for the explosive quality
of dust. I will for forever remember the wall of heat that over took me
while I was admiring the way the dust had billowed up in the rising gasses
of the burning barrel. It was over in milliseconds, left no permanent scars,
but has left me with the attitude that I will not take any chances with dust
Just for fun I Googled dust explosions, perused the results to see if my
mileage was not too different to others ( didn't want my first post to be
attributed to a raving loony) and I happened upon an image that is a dead
ringer for what is seared into my brain. (pun intended)
I don't know how much of this is relevant to dust collectors, don't really
care, but for my money if there is a chance of setting of something like the
explosion I witnessed and it only takes a couple of dollars and a couple of
hours then I'm in.
I want someone to tell me how they think that wrapping copper wire
around the *outside* of an insulator is going to prevent sparks from
occuring *inside* said insulated space. Since static charge builds up
as a surface charge, I also want to be shown how having a discharge path
on the inside of the collector will actually make the system safer
regarding static discharge from the surface charge. One could postulate
that having the wire on the inside is actually worse, because a
potential from one side of the plastic surface can build up such that a
discharge to the wire residing at some distance from the surface
results. This can become even more of an issue if the wire becomes
airborn, creating a gap for the discharge to take place.
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.
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
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.
I have done electronic work for 35 years. How do you like soldering
in those 82 pin SMDs? <g>
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. <g> 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.
IIRC from my days with NCR, that large resistor was to protect you from the
rare possibility you *might* get hold of some 120VAC. Theoretically you
could grab a live lead with the other hand and not even feel it with the
large resistor in the static ground lead.(I got tired of the dam wrist strap
and soldered the snap to my watch band)
On Mon, 22 Dec 2003 23:40:41 -0500, Greg G. wrote:
The 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.
On Tue, 23 Dec 2003 01:43:13 -0500, Greg G. wrote:
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.
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.
People spend hundreds for electrostatic filters in the shop. You get yours
free with the PVC.
1) Don't urinate on electric fences when barefoot.
2) Don't lick the pump handle at 20 below.
3) Don't touch your PVC (or your spouse after sliding down the couch to
Results are, in all cases, predictable.
A rational voice rang out from the void, and 6tester said:
Sort of my point. Any remotely combustible product finely atomized
within an oxygen environment will burn at an accelerated rate - and
when constrained by the walls of a DC system, *could* result in an
explosion. Whether big or small doesn't matter - fire is fire.
Apollo Astronauts aren't *supposed* to be char-broiled in their
capsule on the launch pad, but it happened.
Nice fireball! Reminds me of my youth & home-made rocket experiments.
Potential for nice fireballs in your house, no less. I, too, tend to
err on the side of caution. $3 and 20 minutes? Count me in as well.
Opinions are like as%holes - we've all got one.
Oh well, made for a mildly entertaining hour, anyway. <g>
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.