Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?

"nigel" wrote in message
ups.com...
Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?


I can only imagine the static build up that will happen. I am in the middle
of putting up my collector system and the amount of plastic (ABS) shavings
that stick to the cut pipes is amazing. The stuff is everywhere. Stuck to
the saw, the walls, the piping, me; I mean everywhere. I will definitely
have to try to ground this somehow. I was thinking of grounding to nearby
110V outlet cover plate screws. Is this a viable way to go?

Paul

On 13 Nov 2004 12:57:13 -0800, "nigel" wrote:

Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?

If your tubing is metal, that will dissipate the static charges. I
have plastic tubing with a spiral wire embedded. I used to get static
shocks before I grounded the wire.

On Sat, 13 Nov 2004 21:01:39 GMT, "Paul in MN"
wrote:


"nigel" wrote in message
oups.com...
Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?


I can only imagine the static build up that will happen. I am in the middle
of putting up my collector system and the amount of plastic (ABS) shavings
that stick to the cut pipes is amazing. The stuff is everywhere. Stuck to
the saw, the walls, the piping, me; I mean everywhere. I will definitely
have to try to ground this somehow. I was thinking of grounding to nearby
110V outlet cover plate screws. Is this a viable way to go?

Paul


That will work if the screw is indeed grounded, but it is better to
use a pipe you know is buried into the ground.

Phisherman wrote:
On Sat, 13 Nov 2004 21:01:39 GMT, "Paul in MN"
wrote:


"nigel" wrote in message
ups.com...
Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect
it to DC and machine grounds at each end.

I imagine this is only a problem with plastic tubes/conduits ...
metal would seem to be proof against the whole thing.
What do the experts have to say on this?


I can only imagine the static build up that will happen. I am in
the middle of putting up my collector system and the amount of
plastic (ABS) shavings that stick to the cut pipes is amazing. The
stuff is everywhere. Stuck to the saw, the walls, the piping, me; I
mean everywhere. I will definitely have to try to ground this
somehow. I was thinking of grounding to nearby 110V outlet cover
plate screws. Is this a viable way to go?

Paul


That will work if the screw is indeed grounded, but it is better to
use a pipe you know is buried into the ground.

I had a lot of electrical "book learnin'" in kollege but my practical
knowledge is very low. In this situation, grounding a DC to a good earth
ground, should there be a current-limiting resistor somewhere between the
water pipe and wire going through the DC system? If so, what size?

Thanks.

-- Mark

On 13 Nov 2004 12:57:13 -0800, "nigel" wrote:

Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.

This is really stupid when you think about the fact that you're
wrapping wire around an insulating material. G

Slide a wire tap along the coil, and tune radio stations!

Barry

"Mark Jerde" wrote in message
newstvld.1341$GV5.185@trnddc04...

I had a lot of electrical "book learnin'" in kollege but my practical
knowledge is very low. In this situation, grounding a DC to a good earth
ground, should there be a current-limiting resistor somewhere between the
water pipe and wire going through the DC system? If so, what size?


It's not necessary since the connection keeps the wire at the same potential
(or very close to) ground. There is a very small current flowing through
the wire. To install a resistor would guarantee that the wire has a small
potential on it.

"nigel" wrote in message
ups.com...
Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.


Only make the connection at one point. The most logical point would be to
ground the wire at the DC end. Run wires out all the way to the ends where
your machines hook up to it but don't connect it at that point. Ground
should only connected at one point.

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?

The pipe itself is the conductor in metal systems and should still be
grounded at one point.

"nigel" wrote in message
ups.com...

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?

You can ground the system if you have problem with getting shocks from it.
Its not necessary, from a safety point of view. I liive in Houston where
the humidity is relatively high and I have no problems at all running
ungrounded.

Bob

Frank Ketchum wrote:
"Mark Jerde" wrote in message
newstvld.1341$GV5.185@trnddc04...

I had a lot of electrical "book learnin'" in kollege but my practical
knowledge is very low. In this situation, grounding a DC to a good
earth ground, should there be a current-limiting resistor somewhere
between the water pipe and wire going through the DC system? If so,
what size?


It's not necessary since the connection keeps the wire at the same
potential (or very close to) ground. There is a very small current
flowing through the wire. To install a resistor would guarantee that
the wire has a small potential on it.

I got the idea from (IIRC) the "grounding straps" sometimes used when
repairing computers. It's my understanding these all have a resistor in
them to limit the current flowing through the repair-person in the event of
current-to-ground.

As a kid I was badly shocked by 1960's era tools (*) and I admit I may be
overly concerned about a direct circuit to ground (especially since the
ground wire of a standard 3-prong outlet does the same thing if I understand
home wiring correctly). But suppose I'm concerned about doing something
really stupid like grabbing the DC grounding wire in a sweaty hand, then
biting through the cord of my Skilsaw. Would a properly-sized resistor
between the DC grounding wire and ground help in this situation?

-- Mark

(*) Most memorable: I turned on a sheep shearing machine, got a whale of a
shock, couldn't turn it off and had a hard time letting go. :-(
Fortunately the floor of the sheepshed was fairly dry and I was finally able
to drop the d*mn thing. If the manure had been fresh it may have killed me.

On Sat, 13 Nov 2004 21:59:49 GMT, "Mark Jerde"
wrote:

In this situation, grounding a DC to a good earth
ground, should there be a current-limiting resistor somewhere between the
water pipe and wire going through the DC system?

No.

Resistors in grounding systems are only there when grounding
personnel. It's not needed for static, but it can save lives. An
accidental mains-voltage electric shock can be painful in a typical
situation, but fatal if you have an arm grounded with a low-impedance
path to ground. A mere few megohms makes no difference to grounding
effectiveness, but it's a significant barrier to mains voltages.

--
Smert' spamionam

On 13 Nov 2004 12:57:13 -0800, "nigel" wrote:

Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around.

It builds up. If this is a nuisance to you, then ground it.

There's no safety hazard to static discharge (in a woodworking DC).
The two real safety risks are static discharge mixed with flammable
solvent vapour, or sucking up a hot ember into the dust stream.

Grounding is hard to do reliably. An internal wire will suffer dust
erosion. The worst case for static buildup is a metal flange in the
plumbing that's insulated by plastic pipe (it creates a capacitor), so
make sure that such things are earthed by external bonding wires.
--
Smert' spamionam

Andy Dingley wrote:
On Sat, 13 Nov 2004 21:59:49 GMT, "Mark Jerde"
wrote:

In this situation, grounding a DC to a good earth
ground, should there be a current-limiting resistor somewhere
between the water pipe and wire going through the DC system?

No.

Resistors in grounding systems are only there when grounding
personnel. It's not needed for static, but it can save lives. An
accidental mains-voltage electric shock can be painful in a typical
situation, but fatal if you have an arm grounded with a low-impedance
path to ground. A mere few megohms makes no difference to grounding
effectiveness, but it's a significant barrier to mains voltages.

Suppose I'm (irrationally) afraid of doing something stupid, like wrapping
the DC ground wire 12 times around my arm, then shooting a 16d nail through
my thumb into the live hot wire on my Skilsaw. What are the specs for a
resistor to put between the DC grounding system and the water pipe to limit
the current flow yet allow for DC static discharge?

Or can someone talk me out of a fear of an open megaamp path-to-ground
throughout my shop?

Thanks.

-- Mark

What do the experts have to say on this?


To date none of the experts have come up with a single
itty-bitty bit of evidence that PVC piping will lead to a
dust collector explosion.

That's the facts, the whole facts and nothing but the facts.

UA100, stopping at the Lancome' counter after suiting up to
go fly with Grandma, over the Sinai of course...

"Mark Jerde" wrote in message
news:yawld.1482$N_5.603@trnddc03...


I got the idea from (IIRC) the "grounding straps" sometimes used when
repairing computers. It's my understanding these all have a resistor in
them to limit the current flowing through the repair-person in the event
of
current-to-ground.

Techs don't ground themselves when working on live power which is the only
way that current could flow. That would be dangerous. Grounding is used to
dissipate static electricity so that circuits aren't damaged. These are
circuits that are being worked on with no power. It would serve no purpose
to put any kind of a current limiting resistor in the ground path to
dissipate static electricity. In fact, it would be counterproductive.


As a kid I was badly shocked by 1960's era tools (*) and I admit I may be
overly concerned about a direct circuit to ground (especially since the
ground wire of a standard 3-prong outlet does the same thing if I
understand
home wiring correctly). But suppose I'm concerned about doing something
really stupid like grabbing the DC grounding wire in a sweaty hand, then
biting through the cord of my Skilsaw. Would a properly-sized resistor
between the DC grounding wire and ground help in this situation?


No resistor would help that kind of foolishness. BTW - your body is more of
a resistor than the wire, so in effect there is already a current limiting
resistor in the circuit. I think you should stay away from electrical
appliances though - at least until you get your fear of doing stupid things
under control a bit...
--

-Mike-

"Mark Jerde" wrote in message
news:_Kxld.2531$GV5.1353@trnddc04...

Or can someone talk me out of a fear of an open megaamp path-to-ground
throughout my shop?


Your shop is protected by circuit breakers or fuses of lets say 20 amps
(depending on the branch circuit). Megaamps as you call it won't happen in
a direct short from hot to neutral. Your body is in effect a limiting
resistor if it makes the connection. The bottom line is adding some
resistor in the system will only cause problems for you and will not prevent
you from mutilating yourself if you put your mind to it.

Frank

On Sat 13 Nov 2004 02:57:13p, "nigel" wrote in
ups.com:
I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?

Did anybody catch that Mythbusters show where they tried to make the
Static Canon?

The myth is that a construction worker finds a really nice piece of large
diameter, about 8-10 inch, plastic pipe and wants to use it but it's all
dirty so he sandblasts it at the site and builds up such a huge static
charge on it that when he walks around its end, it shoots a lightning
bolt out of it and blows him across the compound.

They tried everything. Couldn't even make the thing spark. They had a
voltmeter on it, and it kept building up a little charge and then
dissipating.

As someone else has said, the stuff is an insulator. Grounding the
outside grounds only the outside. Don't need a resistor, you're only
sending a few volts to the ground. But any charge inside the pipe is
still there.

I've also seen articles on attempts to duplicate a shop explosion. They
found that the dust particles have to be a certain size, and be dispersed
in the air in such a way that each ignited particle ignites the particle
next to it, and in such a manner that it creates an explosion-like
combustion. They found that when they finally got the conditions correct
for a dust explosion, the air was so full of fine-particle dust they
could barely see. And any air currents in the area screwed it up. The
dust particles weren't close enough together. Their conclusion was, if
you have the correct conditions to create a dust explosion, you should be
more worried about breathing than an explosion.

Want me to hunt around for the article? I think it might have been posted
to this very newsgroup.

Dan

Frank Ketchum wrote:
"Mark Jerde" wrote in message
news:_Kxld.2531$GV5.1353@trnddc04...

Or can someone talk me out of a fear of an open megaamp
path-to-ground throughout my shop?


Your shop is protected by circuit breakers or fuses of lets say 20
amps (depending on the branch circuit). Megaamps as you call it
won't happen in a direct short from hot to neutral. Your body is in
effect a limiting resistor if it makes the connection. The bottom
line is adding some resistor in the system will only cause problems
for you and will not prevent you from mutilating yourself if you put
your mind to it.


Agreed that "megaamps" won't happen from hot to neutral. "Could" they
happen from from hot to the DC ground? (Yes, I'm an idiot on these things.)

Thanks.

-- Mark

So the general word is that there's no safety hazard involved - saw
dust is obviously different to flour, for example.

That's what I was looking to be sure about! My new shop will be in a
building that doesn't belong to me and as the lawyers here in europe
are starting to get almost as trigger happy as in the USA I wanted to
be sure I wasn't not making myself negligent through ignorance.
Thanks people ....

Not so sure it's stupid - this is static charge we're talking here, not
anything with a significant current.

Well, what I heard is that Saddam's entire WMD program is based on
this theory and that's why we be having such a hard time finding them
WMD's, 'cause we just walk right on by all a these PVC pipes laying
around all over the place, not realizing that they only need to be
hooked up to a dust collectorto be turned into explosive deevices,
which is debilishly clebber when ya thinks about it.




On Sat, 13 Nov 2004 20:26:54 -0600, Unisaw A100
wrote:

What do the experts have to say on this?


To date none of the experts have come up with a single
itty-bitty bit of evidence that PVC piping will lead to a
dust collector explosion.

That's the facts, the whole facts and nothing but the facts.

UA100, stopping at the Lancome' counter after suiting up to
go fly with Grandma, over the Sinai of course...

On Sun, 14 Nov 2004 00:35:06 GMT, "Mark Jerde"
wrote:

What are the specs for a
resistor to put between the DC grounding system and the water pipe to limit
the current flow yet allow for DC static discharge?

They're complicated. It's a few megohms (9M from memory) but like any
of these high value resistors, you have to account for construction
and surface paths as much as the resistor itself, and especially
guarding against failure modes that could cause a short. Usual HT
practice is to never use a single resistor anyway, but to use smaller
ones in series. If one fails short, it's just a small change in
resistance, not an overall short.

UK practice is to buy a plugtop. This fits in a standard bench power
outlet, is bright yellow and has a number of press-stud connectors on
the top. Inside is the right sort of resistor, bonding you to the
mains ground. If your bench was built for electronics work, then it
might have such connectors built in anyway. Static wrist strap

Or can someone talk me out of a fear of an open megaamp path-to-ground
throughout my shop?

For the question of "What sort of minimum resistance makes me vague
safe ?" then it's hard to answer. But a resistor of just 27 kilohms
would limit current to under 10mA, and that's going to reduce the
serious hazard massively.

NB - I'm not suggesting static straps with 27k resistors !

So I hope that shows that putting in even a relatively low resistance
to the ground path can keep the fault current non-lethal.

As a rather gruesome example, there was a recent UK case (discussed at
length in uk.d-i-y) where the daughter of a TV presenter (?) was
electrocuted in their kitchen. A metal pan rack had been installed
over the cooker and the mounting screw had nicked a cable in the wall
(the cable had been improperly routed and not correctly protected).
For some time the family had experienced a tingle from this rack, but
done nothing about it. Finally the victim was killed by it, because
one day her ankle also happened to be touching the well-earthed and
low-impedance case of the dishwasher (there was a contact burn on her
ankle aferwards).


--
Smert' spamionam

In article .com,
nigel wrote:

So the general word is that there's no safety hazard involved - saw
dust is obviously different to flour, for example.

True, but MDF dust is not much different than flour.

Lou

nigel did say:

as the lawyers here in europe
are starting to get almost as trigger happy as in the USA

Sorry to hear that.

--
New project = new tool. Hard and fast rule.

Andy Dingley wrote:

Thanks for the informative post.

As a rather gruesome example, there was a recent UK case (discussed at
length in uk.d-i-y) where the daughter of a TV presenter (?) was
electrocuted in their kitchen. A metal pan rack had been installed
over the cooker and the mounting screw had nicked a cable in the wall
(the cable had been improperly routed and not correctly protected).
For some time the family had experienced a tingle from this rack, but
done nothing about it. Finally the victim was killed by it, because
one day her ankle also happened to be touching the well-earthed and
low-impedance case of the dishwasher (there was a contact burn on her
ankle aferwards).

So my fears aren't, um, groundless. ;-)

-- Mark

In article _Kxld.2531$GV5.1353@trnddc04, "Mark Jerde" wrote:

Or can someone talk me out of a fear of an open megaamp path-to-ground
throughout my shop?

I'll try. I don't know if this will talk you out of your fear, or increase it
to the point that you won't ever walk into the shop again, but here goes. :-)

Every metal-framed tool in the shop that has a three-conductor power cord
plugged into a properly grounded outlet constitutes "an open megamp
path-to-ground".

The same is also true of most, if not all, of your major appliances such as
your refrigerator or your washer.

--
Regards,
Doug Miller (alphageek-at-milmac-dot-com)

Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter
by sending email to autoresponder at filterinfo-at-milmac-dot-com
You must use your REAL email address to get a response.

In article FXBld.1912$BX4.883@trnddc08, "Mark Jerde" wrote:

Agreed that "megaamps" won't happen from hot to neutral. "Could" they
happen from from hot to the DC ground? (Yes, I'm an idiot on these things.)

Absolutely not. The circuit breaker (or fuse, as the case may be) limits the
current that can flow through the hot conductor -- without regard to where
it's flowing to.

--
Regards,
Doug Miller (alphageek-at-milmac-dot-com)

Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter
by sending email to autoresponder at filterinfo-at-milmac-dot-com
You must use your REAL email address to get a response.

On Sat, 13 Nov 2004 13:57:13 -0700, nigel wrote
(in article . com):

Following on from the recent DC discussion ... what is the deal with
static charge buildup with all this dust flying around. I've heard
recommendations to add wire spirals around the tubing and connect it to
DC and machine grounds at each end.

I imagine this is only a problem with plastic tubes/conduits ... metal
would seem to be proof against the whole thing.
What do the experts have to say on this?


I read somewhere on-line (the dust collection info site?) about a factory
using PVC and how everyone would get nasty static shocks from it. They tried
the usual tricks of wire, etc but none really worked. What finally did work
was a strip of the metal (aluminum ?) duct tape in a strip along the inside
of the PVC and another strip along the outside. The two strips were then
connected together with several holes drilled through the pipe wall and
fastened with a bolt and washers. This was then earth grounded. Something
about the greater surface area of the conductor in the pipe doing a better
job of collecting those pesky extra electrons....
-Bruce

On Sun, 14 Nov 2004 11:22:12 -0700, Bruce wrote:

I read somewhere on-line (the dust collection info site?) about a factory
using PVC and how everyone would get nasty static shocks from it. They
tried the usual tricks of wire, etc but none really worked. What finally
did work was a strip of the metal (aluminum ?) duct tape in a strip along
the inside of the PVC and another strip along the outside. The two strips
were then connected together with several holes drilled through the pipe
wall and fastened with a bolt and washers. This was then earth grounded.
Something about the greater surface area of the conductor in the pipe
doing a better job of collecting those pesky extra electrons.... -Bruce

Musta been fun getting that tape on the inside of the pipe...

-Doug

Mike Marlow wrote:


"Mark Jerde" wrote in message
news:yawld.1482$N_5.603@trnddc03...


I got the idea from (IIRC) the "grounding straps" sometimes used when
repairing computers. It's my understanding these all have a resistor in
them to limit the current flowing through the repair-person in the event
of
current-to-ground.

Techs don't ground themselves when working on live power which is the only
way that current could flow. That would be dangerous. Grounding is used
to
dissipate static electricity so that circuits aren't damaged. These are
circuits that are being worked on with no power. It would serve no
purpose to put any kind of a current limiting resistor in the ground path
to
dissipate static electricity. In fact, it would be counterproductive.

First, only a very tiny current through the heart is likely to be fatal. You
don't need megaamps, or amps, 60 milliamps can do it. Second, while techs
don't ground themselves when working on high voltage, they do ground
themselves while working inside computers, and the grounding devices (wrist
straps are one kind, but there are others) always have resistors in the
cord specifically to prevent such an accident.

As a kid I was badly shocked by 1960's era tools (*) and I admit I may be
overly concerned about a direct circuit to ground (especially since the
ground wire of a standard 3-prong outlet does the same thing if I
understand
home wiring correctly). But suppose I'm concerned about doing something
really stupid like grabbing the DC grounding wire in a sweaty hand, then
biting through the cord of my Skilsaw. Would a properly-sized resistor
between the DC grounding wire and ground help in this situation?


No resistor would help that kind of foolishness. BTW - your body is more
of a resistor than the wire, so in effect there is already a current
limiting
resistor in the circuit.

Not good enough to prevent death though.

I think you should stay away from electrical
appliances though - at least until you get your fear of doing stupid
things under control a bit...

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

"J. Clarke" wrote in message
...
Mike Marlow wrote:


"Mark Jerde" wrote in message
news:yawld.1482$N_5.603@trnddc03...


I got the idea from (IIRC) the "grounding straps" sometimes used when
repairing computers. It's my understanding these all have a resistor
in
them to limit the current flowing through the repair-person in the
event
of
current-to-ground.

Techs don't ground themselves when working on live power which is the
only
way that current could flow. That would be dangerous. Grounding is
used
to
dissipate static electricity so that circuits aren't damaged. These are
circuits that are being worked on with no power. It would serve no
purpose to put any kind of a current limiting resistor in the ground
path
to
dissipate static electricity. In fact, it would be counterproductive.

First, only a very tiny current through the heart is likely to be fatal.
You
don't need megaamps, or amps, 60 milliamps can do it.

I'm not sure I understand why you pointed that out. It wasn't a point under
discussion.

Second, while techs
don't ground themselves when working on high voltage, they do ground
themselves while working inside computers, and the grounding devices
(wrist
straps are one kind, but there are others) always have resistors in the
cord specifically to prevent such an accident.

I was a tech for a lot of years before making career changes and we used
direct ground when working on computers. I've worked on mainframes where we
literally climbed inside the frame all the way to common PC's. I have seen
the resistive wrist straps, but they are far from the only grounding
technique. When concerned for static discharge, which is the primary
concern for computer techs, there is no need for the resistive component. A
direct ground path is equally effective. The accident that the tech is
concerned for when working on a circuit board is the accidental discharge of
static electricity through the board. No need for a resistive element to
address that issue.


As a kid I was badly shocked by 1960's era tools (*) and I admit I may
be
overly concerned about a direct circuit to ground (especially since the
ground wire of a standard 3-prong outlet does the same thing if I
understand
home wiring correctly). But suppose I'm concerned about doing
something
really stupid like grabbing the DC grounding wire in a sweaty hand,
then
biting through the cord of my Skilsaw. Would a properly-sized resistor
between the DC grounding wire and ground help in this situation?


No resistor would help that kind of foolishness. BTW - your body is
more
of a resistor than the wire, so in effect there is already a current
limiting
resistor in the circuit.

Not good enough to prevent death though.


Did you read what he posted? With the type of foolishness he suggested,
there is nothing that can prevent death.
--

-Mike-

On Sun, 14 Nov 2004 05:21:41 GMT, "Mark Jerde"
calmly ranted:

Agreed that "megaamps" won't happen from hot to neutral. "Could" they
happen from from hot to the DC ground? (Yes, I'm an idiot on these things.)

Since the neutral and ground are bonded in the box and there
is less than an ohm of difference between their points on a
solid copper line. Whatever won't happen to one won't happen
to the other. g

Static discharge is from whatever ungrounded area to either
neutral or ground, since they are the eqivalent to any major
static force. Yes, static happens, but it doesn't blow up DC
systems in gar^H^H^Hshops.

-----------------------------------------------
I'll apologize for offending someone...right
after they apologize for being easily offended.
-----------------------------------------------
http://www.diversify.com Inoffensive Web Design

Mike Marlow wrote:


"J. Clarke" wrote in message
...
Mike Marlow wrote:


"Mark Jerde" wrote in message
news:yawld.1482$N_5.603@trnddc03...


I got the idea from (IIRC) the "grounding straps" sometimes used when
repairing computers. It's my understanding these all have a resistor
in
them to limit the current flowing through the repair-person in the
event
of
current-to-ground.

Techs don't ground themselves when working on live power which is the
only
way that current could flow. That would be dangerous. Grounding is
used
to
dissipate static electricity so that circuits aren't damaged. These
are
circuits that are being worked on with no power. It would serve no
purpose to put any kind of a current limiting resistor in the ground
path
to
dissipate static electricity. In fact, it would be counterproductive.

First, only a very tiny current through the heart is likely to be fatal.
You
don't need megaamps, or amps, 60 milliamps can do it.

I'm not sure I understand why you pointed that out. It wasn't a point
under discussion.

Safety was being discussed. Terms like "megaamps" were being thrown around.

Second, while techs
don't ground themselves when working on high voltage, they do ground
themselves while working inside computers, and the grounding devices
(wrist
straps are one kind, but there are others) always have resistors in the
cord specifically to prevent such an accident.

I was a tech for a lot of years before making career changes and we used
direct ground when working on computers. I've worked on mainframes where
we
literally climbed inside the frame all the way to common PC's. I have
seen the resistive wrist straps, but they are far from the only grounding
technique. When concerned for static discharge, which is the primary
concern for computer techs, there is no need for the resistive component.
A
direct ground path is equally effective. The accident that the tech is
concerned for when working on a circuit board is the accidental discharge
of
static electricity through the board. No need for a resistive element to
address that issue.

Be kind enough to tell me where one can obtain a wrist strap that does not
have a resistor installed, and if the purpose of the resistor is not safety
then what is its purpose? Yes, there are other devices with other safety
measures that go with them. But they all have some means of ensuring that
you don't get a low resistance path to ground.

As a kid I was badly shocked by 1960's era tools (*) and I admit I may
be
overly concerned about a direct circuit to ground (especially since
the ground wire of a standard 3-prong outlet does the same thing if I
understand
home wiring correctly). But suppose I'm concerned about doing
something
really stupid like grabbing the DC grounding wire in a sweaty hand,
then
biting through the cord of my Skilsaw. Would a properly-sized
resistor between the DC grounding wire and ground help in this
situation?


No resistor would help that kind of foolishness. BTW - your body is
more
of a resistor than the wire, so in effect there is already a current
limiting
resistor in the circuit.

Not good enough to prevent death though.


Did you read what he posted? With the type of foolishness he suggested,
there is nothing that can prevent death.

This is true, but beside the point, which is that one's body is not a good
enough resistor to prevent electrocution.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

"J. Clarke" wrote in message
...
Mike Marlow wrote:

I was a tech for a lot of years before making career changes and we used
direct ground when working on computers. I've worked on mainframes
where
we
literally climbed inside the frame all the way to common PC's. I have
seen the resistive wrist straps, but they are far from the only
grounding
technique. When concerned for static discharge, which is the primary
concern for computer techs, there is no need for the resistive
component.
A
direct ground path is equally effective. The accident that the tech is
concerned for when working on a circuit board is the accidental
discharge
of
static electricity through the board. No need for a resistive element
to
address that issue.

Be kind enough to tell me where one can obtain a wrist strap that does not
have a resistor installed, and if the purpose of the resistor is not
safety
then what is its purpose? Yes, there are other devices with other safety
measures that go with them. But they all have some means of ensuring that
you don't get a low resistance path to ground.

The wrist strap is not the universal grounding method. There are pads that
techs stand on and slap bars the are used to discharge static - the pad
preventing the buildup of static after the discharge. There are grounded
pads that components are placed on. There is the method of clamping ground
straps/braids directly to the object. There are even wrist and foot straps
that do not contain any resistive elements. The point being - you do not
need a resistor in series to safely discharge static electricity. Don't
confuse what you can find in tech repair areas where they deal with risks
(to the component, not to themselves) from extreemly minute levels of static
discharge with what you need to discharge static in other environments.



Did you read what he posted? With the type of foolishness he suggested,
there is nothing that can prevent death.

This is true, but beside the point, which is that one's body is not a good
enough resistor to prevent electrocution.


Never claimed it was. Just pointed out the foolishness of his scenario.

--

-Mike-

In article k.net,
"Mike Marlow" wrote:

The point being - you do not
need a resistor in series to safely discharge static electricity.

I think you misunderstand the purpose of the resistor; AFAIK it is not
to safely discharge *static* electricity, it is to prevent you from much
higher chance of death in the event of electrocution, for example if you
should touch the mains. One of the most dangerous scenarios is when one
hand touches the mains and the other is grounded; this puts the current
directly across the heart. Wearing a wrist strap is just begging for
trouble in the event of an accident. A resistor mitigates this risk.

PK

"Unisaw A100" wrote in message
...
What do the experts have to say on this?


To date none of the experts have come up with a single
itty-bitty bit of evidence that PVC piping will lead to a
dust collector explosion.

That's the facts, the whole facts and nothing but the facts.

UA100, stopping at the Lancome' counter after suiting up to
go fly with Grandma, over the Sinai of course...

Interesting. So.....

In the book Woodshop Dust Control, Sandor
Nagisygnskfiwef(something-or-other) recommends that the reader NOT use
plastic pipe for the DC system, and shows a lot of detail on grounding
plastic pipe to prevent an explosion. He seems to consider it a real risk.

Yet the concensus here is that it's not a risk in a small-shop environment.
(also other threads have pointed to some good sources of info on why an
explosion is unlikely).

In that book, he also recommends that a DC not be located near a furnace or
water heater - appliances with a pilot light. Is he being overly cautious
in this warning, too? As long as the DC has decent bags so it's not blowing
dust right through, how likely is it that there would be a high enough
concentration of dust to be ignited from a pilot light?

"Keith Carlson" wrote in message
news:6m2md.408724$D%.261058@attbi_s51...
"Unisaw A100" wrote in message
...
What do the experts have to say on this?


To date none of the experts have come up with a single
itty-bitty bit of evidence that PVC piping will lead to a
dust collector explosion.

That's the facts, the whole facts and nothing but the facts.

UA100, stopping at the Lancome' counter after suiting up to
go fly with Grandma, over the Sinai of course...

Interesting. So.....

In the book Woodshop Dust Control, Sandor
Nagisygnskfiwef(something-or-other) recommends that the reader NOT use
plastic pipe for the DC system, and shows a lot of detail on grounding
plastic pipe to prevent an explosion. He seems to consider it a real risk.

Yet the concensus here is that it's not a risk in a small-shop
environment.
(also other threads have pointed to some good sources of info on why an
explosion is unlikely).

In that book, he also recommends that a DC not be located near a furnace
or
water heater - appliances with a pilot light. Is he being overly cautious
in this warning, too? As long as the DC has decent bags so it's not
blowing
dust right through, how likely is it that there would be a high enough
concentration of dust to be ignited from a pilot light?



Well - even though I'm not answering your questions, let me throw another
twist into the game. Explosive environments, and by that I mean truly
explosive environments, require electrical switches that are rated for that
environment, so that the spark that typically occurs when you throw your
basic household light switch, does not cause an explosion. So - when was
the last time you heard of a dust explosion in a woodworking shop from a
light switch being thrown? I realize you could make an argument that an
open flame is a higher concentration of heat than a spark, if the threat of
explosion was truly as great as is claimed by some, wouldn't you think there
would be at least a mention of explosive environment light switches?
--

-Mike-

"Paul Kierstead" wrote in message
news
In article k.net,
"Mike Marlow" wrote:

The point being - you do not
need a resistor in series to safely discharge static electricity.

I think you misunderstand the purpose of the resistor; AFAIK it is not
to safely discharge *static* electricity, it is to prevent you from much
higher chance of death in the event of electrocution, for example if you
should touch the mains. One of the most dangerous scenarios is when one
hand touches the mains and the other is grounded; this puts the current
directly across the heart. Wearing a wrist strap is just begging for
trouble in the event of an accident. A resistor mitigates this risk.

PK

Well, I understand this, but I would have to wonder why anyone would wear a
wrist strap when working with the mains. Touch the mains with one hand and
ground with the other and a resistive ground strap isn't going to help you
one bit. How much current is any resistor built into a wrist strap going to
take? How long is that going to afford any protection - if it afforded any
in the first place? If you wanted a device which provided a better path to
ground than through your heart, you would want a non-resistive path. A
simple ground braid. The only purpose I know of for a wrist strap is
specifically for static electricity. I can be educated though - am I
missing something?

--

-Mike-

In article _Kxld.2531$GV5.1353@trnddc04,
Mark Jerde wrote:

Suppose I'm (irrationally) afraid of doing something stupid, like wrapping
the DC ground wire 12 times around my arm, then shooting a 16d nail through
my thumb into the live hot wire on my Skilsaw. What are the specs for a
resistor to put between the DC grounding system and the water pipe to limit
the current flow yet allow for DC static discharge?

Or can someone talk me out of a fear of an open megaamp path-to-ground
throughout my shop?

Thanks.

-- Mark



I don't know about the "megaamp" part of it, but I'll take a shot at
talking you out of it; Every powertool in your shop with a 3 prong
plug, every water pipe, EMT, BX cable, and who knows what else is a
path to ground.


--

Larry Wasserman Baltimore, Maryland

On Mon, 15 Nov 2004 13:41:22 GMT, "Keith Carlson"
wrote:

"Unisaw A100" wrote in message
.. .
What do the experts have to say on this?


To date none of the experts have come up with a single
itty-bitty bit of evidence that PVC piping will lead to a
dust collector explosion.

That's the facts, the whole facts and nothing but the facts.

UA100, stopping at the Lancome' counter after suiting up to
go fly with Grandma, over the Sinai of course...

Interesting. So.....

In the book Woodshop Dust Control, Sandor
Nagisygnskfiwef(something-or-other) recommends that the reader NOT use
plastic pipe for the DC system, and shows a lot of detail on grounding
plastic pipe to prevent an explosion. He seems to consider it a real risk.

yup. he bought the whole load of BS too. it's a shame, 'cause he's a
pretty good teacher.





Yet the concensus here is that it's not a risk in a small-shop environment.
(also other threads have pointed to some good sources of info on why an
explosion is unlikely).

In that book, he also recommends that a DC not be located near a furnace or
water heater - appliances with a pilot light. Is he being overly cautious
in this warning, too? As long as the DC has decent bags so it's not blowing
dust right through, how likely is it that there would be a high enough
concentration of dust to be ignited from a pilot light?


let's make a clear distinction between production shops and home shops
here.

in production shops there are large machines, multiples of them,
running continuously, each making lots of dust. this is an environment
where plastic piping is a hazard and AFAIK illegal.

in home shops this is not the case.

there are plenty of non-static discharge hazards associated with dust
collectors in home shops. big bags of sawdust are a ready source of
fuel just waiting for a source of ignition. vacuum up a cigarette butt
or a nail that sparks off of some metal part inside the DC and you
could have a smouldering fire inside the DC that erupts into full
ignition hours after you've shut off the lights and gone to bed.

I fail to see how a pilot light could do this short of sucking big
piles of dust through the piloted device, but someone somewhere might
be able to pull it off ; ^ ) more likely is that the DC would blow
out the pilot...