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.

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?

I could be that Sandor Nagyszalanczy is referring to a commercial wood shop and
avoiding a law suit.. The book is not just written for the hobbyist.

--
Jack Novak
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)

Mike Marlow wrote:


"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.

One doesn't. But power has a way of appearing unexpectedly on the bench.

Touch the mains with one hand
and ground with the other and a resistive ground strap isn't going to help
you
one bit.

Touch the mains with one hand while wearing a NON-resistive ground strap on
the other and then what?

How much current is any resistor built into a wrist strap going
to
take?

Well, typically the resistor is 1 megohm 1/4 watt, which should be within
its power rating up to 500 volts, at which point the current through it
would be 500 microamps.

How long is that going to afford any protection - if it afforded
any
in the first place?

Unless you're working with more than 500 volts it should provide protection
indefinitely. And when it fails it tends to fail open and break the
circuit rather than fail short.

If you wanted a device which provided a better path
to
ground than through your heart, you would want a non-resistive path.

That is not the purpose of the device.

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?

Yes, you are. The purpose is to eliminate static. The use of the wrist
strap, however, introduces a new danger--a path to ground through the wrist
strap. The resistor is there to eliminate that specific danger by limiting
the amount of current than can flow through that path to a level that is
not dangerous.

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

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

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?

Ahh... yes, a few things in this particular case, which is OK, we all
have mental blocks sometimes.

Who me???? Mental blocks???? Sometimes????????? You're too kind...


- It isn't about working on the mains, but about accidents that happen.

The post I replied to mentioned mains, that's why I comment on them.

A power supply might be plugged in and wired incorrectly, for example.
The oddest things happen. I remember working on a darkroom timer
(digital) once; it had the grounding plug cut off and was wired with the
neutral to the case. The plug was in upside down and I got quite a jolt
from the *case* (this is why it was being serviced). If I had a
non-resistive wrist strap on, the unpleasant experience could have
become a fatal one.

Correct, but in this case no wrist strap would have been better than a
resistive one. The original symptoms called for checking voltage on the
chassis to ground. This is not really a wrist strap issue.

Rule one of working with power: Accidents happen.

Yes they do and doggoneit how comes it always seems that they never happen
to the other guy?

- The resistor limits current a lot. Lets say your body is zero
resistance; a 5 megaohm resistor will limit current to microamps. It
does'nt have to "take" current; it limits the current simply (consult
ohm's law).

The basic problem here is you should not be attaching anything to your body
in the hope it will conduct current like that. You stay away from making
complete paths to ground from high voltage. Again - in this situation, no
wrist strap is better than a resistive one. Consider - the only way your
resistive wrist strap is going to be beneficial is if you have no other path
to ground through your body. You're insulated at the floor and the only
path to ground is that strap. No strap - no path to ground - no current
flow. Conversely, perhaps you're on a conducting surface and you do somehow
have a path to ground besides through the strap - that's the path current is
going to take - not through the 5Mohm resister.


--

-Mike-

Keith Carlson wrote:
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.



As I said,

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.

And this includes Sandor.

UA100, who is mentioned by name on the acknowledgements page
of Sandor's book Power Tools...

Paul Kierstead wrote:
snip
- It isn't about working on the mains, but about accidents that happen.
A power supply might be plugged in and wired incorrectly, for example.
The oddest things happen. I remember working on a darkroom timer
(digital) once; it had the grounding plug cut off and was wired with the
neutral to the case. The plug was in upside down and I got quite a jolt
from the *case* (this is why it was being serviced). If I had a
non-resistive wrist strap on, the unpleasant experience could have
become a fatal one. Rule one of working with power: Accidents happen.
- The resistor limits current a lot. Lets say your body is zero
resistance; a 5 megaohm resistor will limit current to microamps. It
does'nt have to "take" current; it limits the current simply (consult
ohm's law).
- Of course if you have a hand on a ground and touch the other to the
mains, you are in trouble. The point is for the wrist strap not to add
*new* problems; it doesn't solve old ones. That is why the resistor is
there. Again, consult ohms law. Note on really high power stuff, they
trained us initially to put one hand in our back pocket to stop us from
doing stupid things. Here is something to think about: Lean up against a
table or other waist high item; what part touches the table? That is why
you see some techs with their ass stuck well out

Again, you are missing the point a bit about the wrist strap. Yes, it is
to provide protection against static. However, having a ground around
your wrist introduces *new* health hazards, i.e. an increased chance of
electrocution. The resistor mitigates this risk.

That was an excellent explanation, Paul.

Of course, the resistor is only a good idea for those of us that
don't plan our accidents far enough in advance to remove the wrist
strap prior to accidentally contacting operating voltages.

R,
Tom Q.

On Mon, 15 Nov 2004 12:57:49 -0700, wrote:

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

Why ? The physics is the same.

If plastic piping is a no-no for commercial workshops in your
jurisdiction, then that's to reduce the _consequences_ of a fire (and
they do happen, for many reasons). Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.

If I had a roof mounted central DC system, I'd want steel pipe too.
--
Smert' spamionam

On Tue, 16 Nov 2004 03:42:35 +0000, Andy Dingley
wrote:

On Mon, 15 Nov 2004 12:57:49 -0700, wrote:

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

Why ? The physics is the same.

home shops never involve anywhere near the volume of dust needed to
generate a hot static discharge into a dust cloud dense enough to
sustain it. that takes a dust collector in the 40 HP range pulling
from multiple high volume dust producing machines at once. while in
theory a home shop could create the right conditions, in practice it's
never happened and never will.




If plastic piping is a no-no for commercial workshops in your
jurisdiction, then that's to reduce the _consequences_ of a fire (and
they do happen, for many reasons).

not just to reduce the conscequences- also to reduce the sources.



Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.

that's ABS flex, not long straight sections of PVC



If I had a roof mounted central DC system, I'd want steel pipe too.

steel pipe is the preferred installation. for home shops, PVC is very
convenient.

Mike Marlow wrote:


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

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?

Ahh... yes, a few things in this particular case, which is OK, we all
have mental blocks sometimes.

Who me???? Mental blocks???? Sometimes????????? You're too kind...


- It isn't about working on the mains, but about accidents that happen.

The post I replied to mentioned mains, that's why I comment on them.

A power supply might be plugged in and wired incorrectly, for example.
The oddest things happen. I remember working on a darkroom timer
(digital) once; it had the grounding plug cut off and was wired with the
neutral to the case. The plug was in upside down and I got quite a jolt
from the *case* (this is why it was being serviced). If I had a
non-resistive wrist strap on, the unpleasant experience could have
become a fatal one.

Correct, but in this case no wrist strap would have been better than a
resistive one. The original symptoms called for checking voltage on the
chassis to ground. This is not really a wrist strap issue.

Rule one of working with power: Accidents happen.

Yes they do and doggoneit how comes it always seems that they never happen
to the other guy?

- The resistor limits current a lot. Lets say your body is zero
resistance; a 5 megaohm resistor will limit current to microamps. It
does'nt have to "take" current; it limits the current simply (consult
ohm's law).

The basic problem here is you should not be attaching anything to your
body
in the hope it will conduct current like that. You stay away from making
complete paths to ground from high voltage. Again - in this situation, no
wrist strap is better than a resistive one.

From the viewpoint of safety, certainly. From the viewpoint of protecting
an expensive piece of machinery from static damage not so.

Consider - the only way your
resistive wrist strap is going to be beneficial is if you have no other
path
to ground through your body. You're insulated at the floor and the only
path to ground is that strap. No strap - no path to ground - no current
flow.

And no disspation of static.

Conversely, perhaps you're on a conducting surface and you do
somehow have a path to ground besides through the strap - that's the path
current is going to take - not through the 5Mohm resister.

And again you're missing the point. You wear the wrist strap to dissipate
static. Because you are wearing a grounded electrode attached to your
body, if you should come in contact with high voltage, you will get a shock
due to that ground path. The resistor is there to keep you from getting
killed if while wearing a wrist strap for the purpose of dissipating static
you inadvertently come in contact with high voltage.

I don't know why you're having so much trouble with this.



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

Andy Dingley wrote:

On Mon, 15 Nov 2004 12:57:49 -0700, wrote:

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

Why ? The physics is the same.

But the volume of dust handled by the collector may be different. CWG has a
planer that is bigger than my truck. Somehow I think that when it's
turning a piece of 8/4 lapacho into 5/4 it produces a little more in the
way of shavings and dust and whatnot than my 13" Delta.

Whether the volume is high enough to constitute an explosion hazard in the
event of a static discharge in the system, I have no idea.

If plastic piping is a no-no for commercial workshops in your
jurisdiction, then that's to reduce the _consequences_ of a fire (and
they do happen, for many reasons). Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.

If I had a roof mounted central DC system, I'd want steel pipe too.

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

On Mon, 15 Nov 2004 21:36:38 -0700, wrote:

home shops never involve anywhere near the volume of dust needed to
generate a hot static discharge into a dust cloud dense enough to
sustain it.

Nor does a commercial DC. It's not the volume that's the issue, it's
the energy per discharge.

Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.

that's ABS flex, not long straight sections of PVC

How are machines like panel saws connected to a DC in the USA ? Here
we commonly see ten-twenty foot drops of clear flexible PVC.

--
Smert' spamionam

Andy Dingley wrote:

On Mon, 15 Nov 2004 21:36:38 -0700, wrote:

home shops never involve anywhere near the volume of dust needed to
generate a hot static discharge into a dust cloud dense enough to
sustain it.

Nor does a commercial DC. It's not the volume that's the issue, it's
the energy per discharge.

You're right that it's not the volume, it's the concentration. To get an
explosion you need x quantity of suspended particles per unit volume and
you need an ignition source. If the concentration is high enough for an
explosion to occur, then it is not a good idea to rely on the hope that any
discharge will be of too little energy to cause ignition. In a home shop
it's not likely that you'll get that kind of concentration. In a
commercial shop it might be a different story.

Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.

that's ABS flex, not long straight sections of PVC

How are machines like panel saws connected to a DC in the USA ? Here
we commonly see ten-twenty foot drops of clear flexible PVC.


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

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

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?

Very unlikely. The research I've seen (Sorry, I don't have a cite immediately
available) indicates that in order for a dust cloud to support a flame front,
the visibility in the cloud would be on the order of a meter. That's a pretty
thick dust cloud. Based on that, the rule of thumb I use is - If I can still see
the far wall of the shop through the dust, an explosion is the least of my
worries.


Tom Veatch
Wichita, KS USA

On Mon, 15 Nov 2004 21:36:38 -0700, wrote:

steel pipe is the preferred installation. for home shops, PVC is very
convenient.

And MUCH less expensive. I just bought a bunch of the PVC for installing a
cyclone currently on order from Bill Pentz.

Comparitive pricing between a local plumbing supply house for 6" ASTM-D2729 S&D
PVC and the web prices from a well-known woodworking supply house:

Pipe: PVC $8.50 for 10 ft length, Steel $28.00 (+ shipping) for 2 x 5 ft
lengths
Wye: PVC $12.00 each, Steel $60.00 (+ shipping)

Well, you get the idea. Comparative costs for other fittings are similar. But,
there is a wider variety of fittings available in the steel.

Tom Veatch
Wichita, KS USA

On Tue, 16 Nov 2004 09:53:19 -0500, "J. Clarke"
wrote:

Nor does a commercial DC. It's not the volume that's the issue, it's
the energy per discharge.

You're right that it's not the volume, it's the concentration.

It's the concentration and the energy. If there's inadequate energy
in the discharge, it won't ignite. If the concentration is inadequate,
it won't propagate.

However, even low concentration is not a guarantee of safety for wood
dust handling. There's a problem with smouldering and a burning
particle _may_ settle out in a dead-air zone where there's likely to
be a build up of other dust. In forensic examinations of many dust
collector fires, they began not in the filter or the collecting bin,
but at stagnant corners and sudden pipe expansions.

For a real treatment of this problem, read Luttgens & Wilson's
"Electrostatic Hazards" or a similar industry-standard handbook. I
still haven't found one that has evidence of static discharge caused
fires in wood dust.
--
Smert' spamionam

On Tue, 16 Nov 2004 11:44:28 +0000, Andy Dingley
wrote:

On Mon, 15 Nov 2004 21:36:38 -0700, wrote:

home shops never involve anywhere near the volume of dust needed to
generate a hot static discharge into a dust cloud dense enough to
sustain it.

Nor does a commercial DC. It's not the volume that's the issue, it's
the energy per discharge.

dust volume *and* the speed that dust is travelling do have a bearing
on the static charges built up in plastic pipe. high volume + high
speed = large static energy being generated. in systems handling tons
per day like grain silos and millwork factories the risk of static
discharge becomes real. in home shops it's pure unadulterated urban
mythology...





Plastic piping, and unearthed too,
is in regular use for the flexible sections of DC hookups.

that's ABS flex, not long straight sections of PVC

How are machines like panel saws connected to a DC in the USA ? Here
we commonly see ten-twenty foot drops of clear flexible PVC.

and that one machine is unlikely to make enough dust to be a problem.
it's the main trunk lines that do.

"J. Clarke" wrote in message
...


And again you're missing the point. You wear the wrist strap to dissipate
static. Because you are wearing a grounded electrode attached to your
body, if you should come in contact with high voltage, you will get a
shock
due to that ground path. The resistor is there to keep you from getting
killed if while wearing a wrist strap for the purpose of dissipating
static
you inadvertently come in contact with high voltage.

I don't know why you're having so much trouble with this.

You don't? Hell, I admitted to the thick headed syndrome in a previous
reply. Ok - it really is a mental block thing - I got focused on the "fix
one problem at a time and deal with hot chassis as a power problem before
worrying about static" way of thinking. I do see your point about
mitigating the inherent risk of a tether to ground - which in fact is one of
the points I made earlier when I said they were only useful in draining
static and that they shouldn't be used for troubleshooting power problems.
I think the point you were trying to make got lost because that's all I was
seeing. I really can see things pretty well, it's just that sometimes it
takes a while...
--

-Mike-

On Tue, 16 Nov 2004 10:03:07 -0700, wrote:

On Tue, 16 Nov 2004 11:44:28 +0000, Andy Dingley
wrote:

On Mon, 15 Nov 2004 21:36:38 -0700, wrote:

home shops never involve anywhere near the volume of dust needed to
generate a hot static discharge into a dust cloud dense enough to
sustain it.

Nor does a commercial DC. It's not the volume that's the issue, it's
the energy per discharge.

dust volume *and* the speed that dust is travelling do have a bearing
on the static charges built up in plastic pipe. high volume + high
speed = large static energy being generated. in systems handling tons
per day like grain silos and millwork factories the risk of static
discharge becomes real.

In the grain elevator explosions with which I am familiar, static was not
the cause of the explosion, it is usually either a faulty electric motor
that generates a spark (much longer duration and thus more energy supplied
to start the ignition), or an open flame.