Ignoramus19762 fired this volley in
:


Brian Lawson is correct for a series circuit.


No, Ig. The point of highest power dissipation will be. Sorry, but he's
dead (old wive's tale) wrong.

If you had a "short circuit" with a resistance across the short of 10
ohms, and 220V across it, what would you get? (ok... rhetorical..) you'd
get a current of 22amps. 22 amps across 10 ohms would be 4840 watts.
That's a fair bit of heat.

Now "conduct" the same experiment with 10 gigaohms.

Tell me how much heat you generate, and whether or not it's discernable
against the background.

In _any_ given circuit, the "highest heat" will be generated in the
highest resistance portion of the circuit, but it's a fool's exercise if
no measurable current flows. The friggin' guilds are teaching these guys
that 10 million megohms of resistance constitutes a "high heat" short in
a 220V line. They don't even _know_ what the term "insulation
resistance" means.

I've had more than one "trained electrician" give me that crap.

I also watched one blow off two fingers with a "lowest resistance" short
in a 440 3-ph panel.

In the end, power supply circuits are limited in current, but you don't
know, can't tell, and will never be informed of what the resistance of
the circuit is. It might not even be limited by resistance. It could be
an inductive reactance issue.

Keep the idea "maximum power" at max(I2R). It's not the greatest R, it's
the greatest product of I2 * R.

LLoyd


LLoyd

Ignoramus19762 fired this volley in
:

Brian Lawson is correct for a series circuit.

Ok... let me back down one step on this.

Brian is correct that the highest heating -IN_THE_CIRCUIT- will be from
the highest resistance point in it.

My contention, though, is that it's useless information. If the highest
heat generated is indiscernable, or if the highest heat might possibly be
many times what's necessary to fuse all the wires and turn them to vapor,
you'd better know what that number is.

It's whatever resistance maximizes I^2R.

Ok? Clear?

LLoyd

On Mon, 03 Oct 2011 17:05:07 -0500, Ignoramus19762
wrote:

I am afraid that this washing down of dusty electrical outlets may
create more problems.


"In the history of mankind, there have always been men and women who's goal
in life is to take down nations. We have just elected such a man to run our
country." - David Lloyyd (2008)

On Mon, 03 Oct 2011 19:51:39 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Ignoramus19762 fired this volley in
m:


Brian Lawson is correct for a series circuit.


No, Ig. The point of highest power dissipation will be. Sorry, but he's
dead (old wive's tale) wrong.

If you had a "short circuit" with a resistance across the short of 10
ohms, and 220V across it, what would you get? (ok... rhetorical..) you'd
get a current of 22amps. 22 amps across 10 ohms would be 4840 watts.
That's a fair bit of heat.

Now "conduct" the same experiment with 10 gigaohms.

Tell me how much heat you generate, and whether or not it's discernable
against the background.

In _any_ given circuit, the "highest heat" will be generated in the
highest resistance portion of the circuit, but it's a fool's exercise if
no measurable current flows. The friggin' guilds are teaching these guys
that 10 million megohms of resistance constitutes a "high heat" short in
a 220V line. They don't even _know_ what the term "insulation
resistance" means.

I've had more than one "trained electrician" give me that crap.

I also watched one blow off two fingers with a "lowest resistance" short
in a 440 3-ph panel.

In the end, power supply circuits are limited in current, but you don't
know, can't tell, and will never be informed of what the resistance of
the circuit is. It might not even be limited by resistance. It could be
an inductive reactance issue.

Keep the idea "maximum power" at max(I2R). It's not the greatest R, it's
the greatest product of I2 * R.

LLoyd


LLoyd

So watts the color code for a 10 ohm resistor rated at 4840 Watts ?

On Mon, 03 Oct 2011 13:40:23 -0500, Ignoramus19762
wrote:

On 2011-10-03, David Lesher wrote:
" writes:


My friend had a 440 motor or line short right in front of him in an
elevator motor room. He was temporarily blinded for a couple days. He
said it felt like someone poured sand in his eyes.

OSHA has gotten religion on the arc flash issue. The #1 chance
for such that will kill folks is when you close a large
main/sub-main breaker. They can and do explode outward with
enough force to blow apart cabinets, taking out the chump
standing there closing the breaker.

So, why exactly do they explode? Can you explain?

I should think shorts and overloads. F'rinstance, turning off a
breaker while all the machinery is still running would cause a large
arc, but when the contacts were closed again, the load would be
gigantic--with all of those motors starting again. Inductive startup
current is much greater than running current, as we all know, right?

Part of the danger is probably from all companies cutting corners to
provide exactly, no more, the required material to handle the rated
load. "Cheap" can be a bit more dangerous. Maybe Square D parts are
worth their extreme prices after all.

--
Worry is a misuse of imagination.
-- Dan Zadra

"Ignoramus23561" wrote in message
...
snip--

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

i

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold

Ignoramus19762 wrote:

On 2011-10-03, Bruce L. Bergman (munged human readable) wrote:
Iggy: Don't screw around with this - take some time, get a Dust
Collector system or a good Shop Vac with a HEPA element and your big
air compressor, use a cross-draft and blow it toward the vacuum hose.
Clean up and out EVERYTHING in the shop area, starting with the
rafters and working down. Take apart the light fixtures, the boxes
for the building wiring, everywhere.

My plan has solidified.

I would do the following.

0. Put on eye protection.
1. Kill all power to the building.
2. For every hanging connector:
- Get a ladder under it and climb it
- Open up the connector
- Clean with a bristle brush
- Close it
- Raise it up by at least 2 feet, forming a loop

I figure, if I need to ever hook up a machine to a hanging connector,
I can always get a ladder in place, it will not be very frequent.


How about a couple screen door springs, instead of tying them in a
loop? Then all you need is a hook on a pole to pull them down to where
you can use them.


--
You can't have a sense of humor, if you have no sense.

On 2011-10-04, Harold & Susan Vordos wrote:

"Ignoramus23561" wrote in message
...
snip--

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

i

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?

i

On 2011-10-04, Michael A. Terrell wrote:

Ignoramus19762 wrote:

On 2011-10-03, Bruce L. Bergman (munged human readable) wrote:
Iggy: Don't screw around with this - take some time, get a Dust
Collector system or a good Shop Vac with a HEPA element and your big
air compressor, use a cross-draft and blow it toward the vacuum hose.
Clean up and out EVERYTHING in the shop area, starting with the
rafters and working down. Take apart the light fixtures, the boxes
for the building wiring, everywhere.

My plan has solidified.

I would do the following.

0. Put on eye protection.
1. Kill all power to the building.
2. For every hanging connector:
- Get a ladder under it and climb it
- Open up the connector
- Clean with a bristle brush
- Close it
- Raise it up by at least 2 feet, forming a loop

I figure, if I need to ever hook up a machine to a hanging connector,
I can always get a ladder in place, it will not be very frequent.


How about a couple screen door springs, instead of tying them in a
loop? Then all you need is a hook on a pole to pull them down to where
you can use them.



I would rather just climb a ladder. It is simpler and not any more
bothersome.

i

On 2011-10-04, Gunner Asch wrote:
On Mon, 03 Oct 2011 17:05:07 -0500, Ignoramus19762
wrote:

I am afraid that this washing down of dusty electrical outlets may
create more problems.

Exactly, I am voicing objections to that idea, not supporting it.

i


"In the history of mankind, there have always been men and women who's goal
in life is to take down nations. We have just elected such a man to run our
country." - David Lloyyd (2008)

On 2011-10-04, Pete Keillor wrote:
On Mon, 03 Oct 2011 15:30:44 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Ignoramus19762 fired this volley in
om:

Right, but why does the arc flash in the first place?

All electricity needs is a low-enough resistance path to start flowing,
and as it raises the temperature of its surrounds (say, by fusing the
metal grinding dust that started the connection), the air itself becomes
a conductor.

A "spark" is nothing more than the voltage overcoming the insulation
resistance of the air; when it begins to flow through the air, it heats
the gasses to plasma temps, and that's what you see as the "spark". If
something like a filament of lathe turning can assist in starting that
current flowing, all the easier for a big, fat arc to form.

Such an arc can form from having foreign material between the leads (like
your 3ph box), or it can form from having two high-voltage leads too
close together. Excess humidity shortens the required gap.

The "classic" man-killer short happens when an inattentive technician
creates a dead-short with a tool, then the tool AND the air around it
vaporize into plasma.

LLoyd

Plus a whole lot of copper vapor. Blown switchgear at my old company
has vaporized pounds of copper. This was more often 2300V than 480V,
but either one will blow the doors way off. We had to watch movies of
phase to phase faults in our training to work in energized enclosures.
I was approved solely due to the large number of VFD's I had and
needed to program in 480V enclosures. Contrary to normal plant
practice, I used low voltage control circuits. I didn't want live 120
V. stuff behind me on the door to the enclosure when I was inside
programming stuff.

Highest voltage I ever personally switched was 15000 V. Hated that
****.

And I never had to deal with grinding dust in my stuff. Water once, a
lot of it, but no conductive dust. Yuk. By the way, I was a chemist,
not an electrician. That's R&D for you.

Pete Keillor

I am impressed. I feel lucky to not have 480v in the building.

Here's a good one: http://www.youtube.com/watch?v=-iClXrd50Z8

i

On 2011-10-04, Ignoramus19762 wrote:
I am impressed. I feel lucky to not have 480v in the building.

Here's a good one: http://www.youtube.com/watch?v=-iClXrd50Z8


great demo

http://www.youtube.com/watch?v=-Qq7U7tFsvQ

On Oct 2, 1:37*pm, Ignoramus23561 ignoramus23...@NOSPAM.
23561.invalid wrote:
I had a little bit of a new experience today.

My new place has cables dropped from the ceiling, with receptacles
hanging somewhat above my height.

I was moving a crane and bumped into one of them, nothing big, just a
minor bump. Then I saw that the receptacle was on fire (or rather,
flames were coming out from inside), with small explosions inside.

I ran to the electrical control panel and turned off electricity to
the whole building. The fire stopped.

After a short while, I opened up the receptacle. It turned out that it
was full of grinding dust (! -- how did it get inside) -- and,
apparently, the dust shifted and shorted the contacts. It was a short
circuit, but with a lot of resistance from the dust, so it caught
fire, but did not trip a breaker.

I cut it off and taped the individual wires, but I am now thinking
that I need to take all of those things apart and blow them out with
compressed air.

Comments?

i

Is your fire insurance on the building current?

TMT

Ignoramus19762 wrote:

Michael A. Terrell wrote:

How about a couple screen door springs, instead of tying them in a
loop? Then all you need is a hook on a pole to pull them down to where
you can use them.

I would rather just climb a ladder. It is simpler and not any more
bothersome.


As long as you remember to do it before the machine is in place.


--
You can't have a sense of humor, if you have no sense.

Ignoramus19762 wrote:

Harold & Susan Vordos wrote:

Ignoramus23561 wrote:

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?


The condition of the contacts. Are they clean, or oxidized & pitted?


--
You can't have a sense of humor, if you have no sense.

On Tue, 04 Oct 2011 03:09:42 GMT, "Harold & Susan Vordos"
wrote:


"Ignoramus23561" wrote in message
m...
snip--

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

i

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold

Which is why Ive been snagging and stocking them for years. I think Ive
got 5-6 milk cartons filled with them.


"In the history of mankind, there have always been men and women who's goal
in life is to take down nations. We have just elected such a man to run our
country." - David Lloyyd (2008)

"Ignoramus19762" wrote in message
...
On 2011-10-04, Harold & Susan Vordos wrote:

"Ignoramus23561" wrote in message
...
snip--

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

i

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks.
They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?

i

Not a thing, Iggy, just commenting that if you don't clean them, buying
replacements would be quite expensive. I think you're on the right track
with the cleaning idea.

Harold

Benny Fishhole fired this volley in
:


So watts the color code for a 10 ohm resistor rated at 4840 Watts ?

Nichrome grey.

G

LLoyd

On 2011-10-04, Harold & Susan Vordos wrote:

"Ignoramus19762" wrote in message
...
On 2011-10-04, Harold & Susan Vordos wrote:

"Ignoramus23561" wrote in message
...
snip--

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

i

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks.
They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?

i

Not a thing, Iggy, just commenting that if you don't clean them, buying
replacements would be quite expensive. I think you're on the right track
with the cleaning idea.

OK, thanks, I got it. I was a little slow.

i

On 2011-10-04, Michael A. Terrell wrote:

Ignoramus19762 wrote:

Harold & Susan Vordos wrote:

Ignoramus23561 wrote:

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?


The condition of the contacts. Are they clean, or oxidized & pitted?



They are just fine. The problem is the dust inside.

i

Lloyd E. Sponenburgh wrote:
Benny Fishhole fired this volley in
:

So watts the color code for a 10 ohm resistor rated at 4840 Watts ?

Nichrome grey.

G

LLoyd

Depends on the voltage and frequency as well.

Anyone been reading about how some folks are trying to get things
switched back to DC transmission? Saw that China is doing that at some
new power plant and some "green" outfit says it's the best way to
conserve energy (by eliminating the AC/DC conversions in the power
system). I want to see the conductors they use to shuttle the average
power load from even a small city!!!!

--
Steve W.

On Tue, 04 Oct 2011 12:02:45 -0400, "Steve W."
wrote:

Lloyd E. Sponenburgh wrote:
Benny Fishhole fired this volley in
:

So watts the color code for a 10 ohm resistor rated at 4840 Watts ?

Nichrome grey.

G

LLoyd

Depends on the voltage and frequency as well.

Anyone been reading about how some folks are trying to get things
switched back to DC transmission? Saw that China is doing that at some
new power plant and some "green" outfit says it's the best way to
conserve energy (by eliminating the AC/DC conversions in the power
system). I want to see the conductors they use to shuttle the average
power load from even a small city!!!!

Big Wire up there because the electrons are actually making the trip
instead of just doing "the wave" back and forth in place as AC, but
not all that big - they run the two-wire Pacific DC Intertie at
+500,000V and -500,000V to ground. 1MV between them.

The only real advantage to HVDC transmission (and why they use it at
all, because it is not as efficient) is that the two power grids at
each end don't have to be in frequency sync with each other.

The grid at our end (LA DWP) is ultimately synched to Hoover Dam,
and the other end is probably synched to the Grand Coulee Dam
generators.

One end can be slipping 1/8 Hz because they had some surge loads,
and the other end doesn't have to, and they can still stay linked up.
If they were hard-linked by AC frequency, the tie would have to pop
offline, or drag the other end down to the same speed.

-- Bruce --

Ignoramus19762 writes:

On 2011-10-03, David Lesher wrote:

OSHA has gotten religion on the arc flash issue. The #1 chance
for such that will kill folks is when you close a large
main/sub-main breaker. They can and do explode outward with
enough force to blow apart cabinets, taking out the chump
standing there closing the breaker.

So, why exactly do they explode? Can you explain?


At startup, the usual reason is someone screwed up; and there
is a shorted cable, connection or...

In a case I know, it was a GE ElectoCenter; a housetrailer-size
structure filled with starters. They get shipped in & installed
onto a slab with a crane. Fed with 4160 through the roof; there
was a main breaker, and 3 busbars & gnd running along the wall
behind the main & starter cabinets. It also had a small 240/120
tranformer to power lights/tools/instrumentation.

A friend was working with a contractor on the installation.
With no starters racked in, he closed the main for the first
time so they'd have local power. Little did they know the
busbars had slid down inside the wall & were touching.

The breaker exploded, blowing the locked door open, knocking
Bill onto his side, with 2nd degree burns to his arms and hands.
Behind Bill, the contractor was also down.

The arcing continued, with the feeds down from the pole to the
building finally burning loose, and flapping in the wind -- the
arc would blow them apart [right hand rule] the arc would stop,
and they'd drift togther again .ZAAAP... ZAAAP...

Bill was trying to get up when the contractor ran OVER him, foot
right on his back, going for the utility substation to pull the
primary disconnect. Before he got there, the utility fuses went
"sounding like a 12 ga. going off in my ear BLAM BLAM".

He was in the hospital for 4-5 days.



--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

On Mon, 03 Oct 2011 19:09:42 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Brian Lawson fired this volley in
:

A point to note that amazes me some people don't know.... with
electric current, the point of HIGHEST resistance will be the point of
highest heat(ing). Think about it.

I did. It doesn't. I'm a career electrical engineer, now 'converted to
the dark side' (explosives industry).

IF you even understand Ohm's law, consider that a few hundred megohms in
series with (even) a 575V main won't conduct enough current to even warm
up.

That's a "HIGH" resistance. A complete "open" with no conduction at all
would be the "HIGHEST" resistance. And in that case, no current would
flow, at all. No current, no power dissipation -- no heat. So
obviously, the point of highest resistance does NOT create the highest
heat.

Try this, instead -- a resistance of _exactly_ what will dissipate the
maxiumum POWER across a shunt is the one that will be the point of
highest heat(ing). (hint... heat is energy... power dissipated as heat)

Think about it. If that doesn't work, try looking up Ohm's law and the
power vs. resistance vs. current formulae.

It's a bit amazing to me that the trades still allow this kind of myth to
perpetuate, and even allow them to be the basis of training their
apprentices. But they do; even today, so don't feel deprived.

The Navy was full of this stuff, too. That's one reason why all I ever
wanted out of the Navy was ME.

LLoyd
Hey Lloyd,

You are absolutley right. I was wrong. What WAS I thinking?!?! Never
let common sense interfere with science, eh? Never let 35 years of
work habit get in thenway of the office engineer.

Brian Lawson.

In article ,
says...

On Mon, 03 Oct 2011 16:58:34 -0400, Wes
wrote:

Ignoramus19762 wrote:

OSHA has gotten religion on the arc flash issue. The #1 chance
for such that will kill folks is when you close a large
main/sub-main breaker. They can and do explode outward with
enough force to blow apart cabinets, taking out the chump
standing there closing the breaker.

So, why exactly do they explode? Can you explain?

I can't but I stand to the side of control panel boxes when turning on the main
disconnect. One time seeing a Hoffman box open from the arc flash was enough for me. No,
I didn't do the work, I was a by stander.

Wes
================

Hey Wes,

Our "rule" was: Stand off to the side of the disconnect (ie..not "in
front" of the cabinet door), one hand in pocket, other hand on the
lever, face away before throw. I've had three occasions to be happy I
did, although I still get a ringing in my left ear.

Somebody mentioned replaceable link fuses....they are not legal here
in Ontario anymore, but I have a long wonderful (nobody actuall "hurt"
story) about them when 200 amp links were tripled up, and the 575 volt
elevator motor was a dead short. We couldn't find the disconnect at
all or about 4 feet of the bus duct feeding it, but we did find two
ends of the fuses (that's how we knew about the tripling) and it took
out the whole powerhouse because it made every disconnect along the
way go short...sort of a ripple effect. You could hear them popping
every few seconds throughout the building. By the way, it was the
building maintenance electricians that had done the tripling, and they
should definetly have known better...I say that, becuase they get to
work with hot supplies most of the time, versus construction
electricians who really don't work hot as much.

FWIW, I'm reminded of the time I was talking to my boss about something
or other and there was a loud "bang". We both looked around, nobody
seemed excited, no alarms went off, we went back to what we were doing.
Then there were three more. And a few more after that and smoke started
pouring out of a conference room. One of the engineers, Ben, a West
Point graduate, looked in the conference room, dragged a guy out, closed
the door, and pulled the fire alarm. A few minutes later the
administrative assistant to the vice president for our division went
into the conference room and started pulling out furniture. Ben argued
with him for a while and finally punched his lights out. About that
time somebody among the Powers That Be grew a brain and ordered the
building to be evacuated.

Turns out that the guy who Ben pulled out was a phone technician who for
reasons unknown had run a steel fish tape through a live conduit that
was feeding a bank of 500 HP motors, and managed to create a short. Why
that conduit came out in a conference room I have no idea.

Ben ended up getting a commendation.

And for Iggy...I've seen 120 volt hanging cables that were in very
damp conitions shorted, and they arc and catch fire and burn like a
dynamite fuse or like a July 4th hand-held "sparkler"...they don't
blow a fuse for about 5 feet.

A point to note that amazes me some people don't know.... with
electric current, the point of HIGHEST resistance will be the point of
highest heat(ing). Think about it.

Take care.

Brian Lawson.

Brian Lawson fired this volley in
:

You are absolutley right. I was wrong. What WAS I thinking?!?! Never
let common sense interfere with science, eh? Never let 35 years of
work habit get in thenway of the office engineer.

You're late, Brian. I already reneged on that blanket statement, and made
one that makes more sense in the context.

(I am the "office engineer" with a whole lot more than 35 years experience
in the field)

LLoyd

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com writes:


A point to note that amazes me some people don't know.... with
electric current, the point of HIGHEST resistance will be the point of
highest heat(ing). Think about it.

I did. It doesn't. I'm a career electrical engineer, now 'converted to
the dark side' (explosives industry).

Got a slot for me? [TBP/EKN]

IF you even understand Ohm's law, consider that a few hundred megohms in
series with (even) a 575V main won't conduct enough current to even warm
up.

That's a "HIGH" resistance. A complete "open" with no conduction at all
would be the "HIGHEST" resistance. And in that case, no current would
flow, at all. No current, no power dissipation -- no heat. So
obviously, the point of highest resistance does NOT create the highest
heat.

The trouble is, the folks teaching fables ignore the major factor:
We have constant voltage supplied by the grid, not constant current!
{In some parallel universe, maybe that's not true...}

{I've used i instead of I to avoid 1|I confusion.}

With a constant voltage source, the i is a function of the R,
and the P is a function of both. If you think constant current,
then R is the only variable factor and yes, higher R is more
power.

Now in reality, the common case RCM types need to think about
is sorta both/neither. Rather, a motor tends to draw constant
power for a given load, and very roughly constant current. Now,
a {maybe loose} connection in its plug has zero to n ohms. At
zero ohms, i^2R is zero; at 1 ohm, 1*i; at 2 ohms 4*i, etc. This
because that resistance is inconsequential in setting the motor
current but IS important in the power dissipated.

.....Now if n gets SO big that the current falls {and of course the
motor stalls/never twitches}...

And THAT is why poor {0 ohm} connections in plugs&splices are Bad Ideas.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

On Mon, 03 Oct 2011 19:51:39 -0500, Lloyd E. Sponenburgh wrote:

Ignoramus19762 fired this volley
in :


Brian Lawson is correct for a series circuit.


No, Ig. The point of highest power dissipation will be. Sorry, but
he's dead (old wive's tale) wrong.

If you had a "short circuit" with a resistance across the short of 10
ohms, and 220V across it, what would you get? (ok... rhetorical..) you'd
get a current of 22amps. 22 amps across 10 ohms would be 4840 watts.
That's a fair bit of heat.

Now "conduct" the same experiment with 10 gigaohms.

Tell me how much heat you generate, and whether or not it's discernable
against the background.

I think you're missing the point.

If you have a circuit with a 10 ohm resistance in series with a 1 ohm
resistance, and 30A flowing through the whole mess, then that's 9000W at
the 10 ohm, and only 900 at the 1 ohm. If they're both about the same
size, then the 10 ohm resistance is going to get 10 times hotter.

So if you have a dirty contact over _there_, and a dead short right
_here_, then the thing that's going to blow up is the thing over _there_.

All this being compounded by the ability of each resistance to dissipate
the heat. Hence the problems with aluminum wiring, where the fire
doesn't start in the lamp with the four 100W light bulbs dropping 110V
out in the air, but in the corroded connection that's dropping 10V buried
in a nice heat-insulating box.

--
www.wescottdesign.com

Tim Wescott fired this volley in
:

I think you're missing the point.


no... I got the point. The real point is you don't know the current
capability of the circuit.

You WILL get the highest heating at the point of highest resistance (or
highest unbalanced inductive reactance) but you usually don't know where
that point is.

Just as a really simplistic example, consider a breaker in series with a
circuit that has (say) .1 ohm across a 220V line. Likely, the _breaker_
will be the point of highest resistance, and the heating will occur
there, not in YOUR "circuit".

You have to know the whole distribution system from end-to-end (at least
from the pole to your device) to know where that point is. That was a
point I didn't make in my original "blanket" statement, and it's the key
one.

LLoyd

On Tue, 04 Oct 2011 12:55:53 -0500, Lloyd E. Sponenburgh wrote:

Tim Wescott fired this volley in
:

I think you're missing the point.


no... I got the point. The real point is you don't know the current
capability of the circuit.

You WILL get the highest heating at the point of highest resistance (or
highest unbalanced inductive reactance) but you usually don't know where
that point is.

Just as a really simplistic example, consider a breaker in series with a
circuit that has (say) .1 ohm across a 220V line. Likely, the _breaker_
will be the point of highest resistance, and the heating will occur
there, not in YOUR "circuit".

You have to know the whole distribution system from end-to-end (at least
from the pole to your device) to know where that point is. That was a
point I didn't make in my original "blanket" statement, and it's the key
one.

Actually, that's the point that I think I was trying to make, without
really articulating it well.


--
www.wescottdesign.com

Ignoramus29750 wrote:

On 2011-10-04, Michael A. Terrell wrote:

Ignoramus19762 wrote:

Harold & Susan Vordos wrote:

Ignoramus23561 wrote:

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?


The condition of the contacts. Are they clean, or oxidized & pitted?



They are just fine. The problem is the dust inside.


Ok. Don't start whining, when some of them start smoking.


--
You can't have a sense of humor, if you have no sense.

Tim Wescott fired this volley in
:

Actually, that's the point that I think I was trying to make, without
really articulating it well.


OK! Then we agree! G

LLoyd

"Michael A. Terrell" fired this volley in
m:

Ok. Don't start whining, when some of them start smoking.

nahhhh... if necessary, disconnect them and wash them with a solvent that
will get all the grinding dust AND coolant out of them.

They're typically bakelite (for the insulators), which is insoluble in just
about everything.

LLoyd

On Tue, 04 Oct 2011 07:36:55 -0500, Ignoramus29750
wrote:

On 2011-10-04, Michael A. Terrell wrote:

Ignoramus19762 wrote:

Harold & Susan Vordos wrote:

Ignoramus23561 wrote:

Well, I kept it. Going through all of them means a few wasted
hours. But I guess I have to bite the bullet and do it.

Your alternative is to buy replacements. You'll experience some serious
sticker shock when you check the price of three phase twist locks. They're
very proud of those suckers.

Harold, why replace them? They are fine, as such, they are simply
dirty and in need of cleaning. What am I missing?


The condition of the contacts. Are they clean, or oxidized & pitted?



They are just fine. The problem is the dust inside.

Why not blow them out?

--
Worry is a misuse of imagination.
-- Dan Zadra

"Lloyd E. Sponenburgh" wrote:

"Michael A. Terrell" fired this volley in
m:

Ok. Don't start whining, when some of them start smoking.

nahhhh... if necessary, disconnect them and wash them with a solvent that
will get all the grinding dust AND coolant out of them.

They're typically bakelite (for the insulators), which is insoluble in just
about everything.


Sigh. I know what the insulators are made of, and some are nylon
instead of bakelite. I was talking about OXIDIZED CONTACTS. They can
oxidize, just sitting on a shelf for years. In an environment of high
humidity and dissimilar metals, they can be in really bad shape. I've
seen them fail in an air conditioned electronics factory. Move a
workbench and discover the outlet gets too hot to touch, when you turn
on the test equipment. No extension cords allowed, per the local
inspectors so you either move the tech to another bench, or send him
home till a grunt from the contract electrical company finally shows
up. I saw it several times in four years, in North Central Florida.
Most of the failed Hubbel twist lock outlets were less than 12 years
old.


--
You can't have a sense of humor, if you have no sense.

On Oct 2, 2:37*pm, Ignoramus23561 ignoramus23...@NOSPAM.
23561.invalid wrote:
I had a little bit of a new experience today.

My new place has cables dropped from the ceiling, with receptacles
hanging somewhat above my height.

I was moving a crane and bumped into one of them, nothing big, just a
minor bump. Then I saw that the receptacle was on fire (or rather,
flames were coming out from inside), with small explosions inside.

I ran to the electrical control panel and turned off electricity to
the whole building. The fire stopped.

After a short while, I opened up the receptacle. It turned out that it
was full of grinding dust (! -- how did it get inside) -- and,
apparently, the dust shifted and shorted the contacts. It was a short
circuit, but with a lot of resistance from the dust, so it caught
fire, but did not trip a breaker.

I cut it off and taped the individual wires, but I am now thinking
that I need to take all of those things apart and blow them out with
compressed air.

Comments?

i

Wow, what excitement. I'm also pretty surprised that none of the 75 or
so responses here suggested that, while blowing them out with
compressed air is a good idea, you should also hold a vacuum cleaner
nozzel nearby to catch the dislodged dust, lest it just settle back
into other (possibly worse) places, your lungs, for instance. While
you're at this, you may want to spend a couple of hours vacuuming any
other horizontal surfaces that may be holding this dust. You really
don't want it raining down off the rafters onto your machinery.

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
. 3.70...
Tim Wescott fired this volley in
:

I think you're missing the point.


no... I got the point. The real point is you don't know the current
capability of the circuit.

You WILL get the highest heating at the point of highest resistance (or
highest unbalanced inductive reactance) but you usually don't know where
that point is.

Just as a really simplistic example, consider a breaker in series with a
circuit that has (say) .1 ohm across a 220V line. Likely, the _breaker_
will be the point of highest resistance, and the heating will occur
there, not in YOUR "circuit".

You have to know the whole distribution system from end-to-end (at least
from the pole to your device) to know where that point is. That was a
point I didn't make in my original "blanket" statement, and it's the key
one.

LLoyd

You get the highest dissipation in the load when its resistance equals the
resistance of the power source. Actually it's equal impedance in AC
circuits, but inductors don't dissipate power as heat. The source in this
case is the pole transformer. At max load power the voltage across the load
will be half the open-circuit value.

Intuitively if the load's resistance is lower than the source's, the source
limits total power, their currents being equal and P=E*I.. If the load's
resistance higher the current through both is less than if they were equal.
In the limiting cases a dead short's current is whatever the source allows
and its voltage drop is zero, so no power. A very high load resistance
limits the current and thus power to a low value.

When you graph the load power vs resistance with the source resistance and
total voltage constant you get a parabola that peaks at equal resistances.

jsw

On 10/03/2011 02:31 PM, Ignoramus19762 wrote:
On 2011-10-03, Lloyd E. Sponenburghlloydspinsidemindspring.com wrote:
fired this volley in
:

So, why exactly do they explode? Can you explain?

Rapid heating (to plasma temperatures) of the air. It gets heated to
several thousands of degrees in a few tens of microseconds. That releases
a physical shock wave (due to the expanding ball of super-heated gas -- if
you don't know them read the Gas Laws) equivalent to a small charge of
explosives.

Right, but why does the arc flash in the first place?

i
OK, in fault conditions, there is a lot of current flowing. There is
inductance in the transformer, wiring, and possibly the load. At 480
and above, it doesn't take a huge inductance to make a substantial arc.
As the breaker is attempting to disconnect the load from the source, it
has to break the arc. This is done by separating the contacts while
the arc is flowing between them. As you separate them, you get a higher
voltage dropped across the arc. Amps times Voltage is power. The
breakers and transformers have some inductance built in to limit
fault currents, but they can develop toward 100 K Amps (that's what
those big 480 breakers are designed to handle one time when interrupting
a major fault.) Well, 100 K amps time 480 V is 48 Million Watts!
That is a HUGE amount of energy, and even if it only is produced for
microseconds, it will go bang. If something is wrong with the breaker,
the installation (to properly limit fault current) etc. then it can be
a major explosion if current flows for milliseconds.

Jon

On 2011-10-04, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
"Michael A. Terrell" fired this volley in
m:

Ok. Don't start whining, when some of them start smoking.

I will not start whining and after cleaning, they will not start
smoking.

nahhhh... if necessary, disconnect them and wash them with a solvent that
will get all the grinding dust AND coolant out of them.

They're typically bakelite (for the insulators), which is insoluble in just
about everything.

I think that just cleaning the insides with a bristle brush, would be
sufficient.

i

On 2011-10-04, Michael A. Terrell wrote:

"Lloyd E. Sponenburgh" wrote:

"Michael A. Terrell" fired this volley in
m:

Ok. Don't start whining, when some of them start smoking.

nahhhh... if necessary, disconnect them and wash them with a solvent that
will get all the grinding dust AND coolant out of them.

They're typically bakelite (for the insulators), which is insoluble in just
about everything.


Sigh. I know what the insulators are made of, and some are nylon
instead of bakelite. I was talking about OXIDIZED CONTACTS. They can
oxidize, just sitting on a shelf for years. In an environment of high
humidity and dissimilar metals, they can be in really bad shape. I've
seen them fail in an air conditioned electronics factory. Move a
workbench and discover the outlet gets too hot to touch, when you turn
on the test equipment. No extension cords allowed, per the local
inspectors so you either move the tech to another bench, or send him
home till a grunt from the contract electrical company finally shows
up. I saw it several times in four years, in North Central Florida.
Most of the failed Hubbel twist lock outlets were less than 12 years
old.

The one connector that I took apart, was not oxidized. I will check
out each of them. Those connectors can be bought for $9.95 online.

i