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Circular saw won't ground, safe?

T

Tim Zimmer

Jan 1, 1970
0
...judging by his lack of response.

I haven't found the time to work on the cord. I will now.

Someone please explain why do some modern factory drills, grinders
and saws get away without a ground plug?

(Here's an ignorant question) Is it true that I can receive a fatal shock if
I touch my skin from either neutral or hot and then ground? If so, then why
not replace the ground with a safer model which doesn't allow a shock?

Lastly, a hot or neutral short to ground shuts down my entire electrical
system. Is this the GFCI?

Thanks
 
J

Jim

Jan 1, 1970
0
Tim Zimmer said:
I haven't found the time to work on the cord. I will now.

Someone please explain why do some modern factory drills, grinders
and saws get away without a ground plug?
In addition to not having a metal case, they are double insulated..
(Here's an ignorant question) Is it true that I can receive a fatal shock if
I touch my skin from either neutral or hot and then ground? If so, then why
not replace the ground with a safer model which doesn't allow a shock?
You won't get much of a shock by simultaneously touching neutral and ground.
You can get a nasty shock by simulataneously touching the hot wire and
either the neutral or ground wires.
Lastly, a hot or neutral short to ground shuts down my entire electrical
system. Is this the GFCI?
No
Jim
 
S

spudnuty

Jan 1, 1970
0
I always double and triple check everything including a final check
with a non contact voltage tester. I've seen so many wierd things
working on clients electrical setups. You know the "What in the
F......" moment and its another one for the books.
This sounds like a pertinent case:
http://www.cdc.gov/niosh/face/stateface/wi/93wi214.html
"A 45-year-old male electrician (the victim) was electrocuted when he
contacted an energized ½-inch metal-cased electric drill.... There were
puddles of water on the cement floor of the work site. The drill was
connected to a temporary power pole by a series of three extension
cords, two of which were missing the ground pin.... The cords were
plugged into a ground fault circuit interrupter (GFCI) receptacle
mounted on the power pole. ... However, testing after the incident
disclosed the GFCI was inoperative, and the fuse box for the 120 volt
single phase 15- and 20-ampere receptacle outlets located at the power
pole contained two 40-ampere fuses."

Richard
 
B

Benoit EVANS

Jan 1, 1970
0
In home accidents in the U.S., one death in every hundred is the result
of an electrical shock from 110 or 220 volt sources.

Injuries from electric shock account for about 1000 deaths annually in
the United States and comprise about 5% of admissions to burn centres.
More than 60% of reported electrical injuries are due to electrocution
with 110- or 220-V current and most commonly result from failure to
ground tools or appliances properly or from using electrical devices
near water. Electrocution is the fifth leading cause of fatal
occupational injuries in the United States; 1% of household accidental
deaths are caused by electrical injuries.

The spectrum of clinical injury from accidental electrical shock ranges
from a transient unpleasant sensation after exposure to low-intensity
current to sudden death due to cardiac arrest. Clinical manifestations
are sometimes seen immediately after contact, but might not become
apparent until several hours after injury.

Source: Fish R. "Electric Shock. Part I: physics and pathophysiology",
Journal of Emergency Medicine, 1993, vol. 11, pp. 309-12.
 
D

Doug Miller

Jan 1, 1970
0
Glad I'm not the only one that does that.

In fact, I do more than that: I plug my tester into something that I'm sure
*is* live, to make sure it lights up when it's supposed to, before using on
something that I believe to be not live.

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

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
 
D

Doug Miller

Jan 1, 1970
0
So you're saying that toller's "research" had a few holes in it? Imagine my
surprise.

Benoit said:
In home accidents in the U.S., one death in every hundred is the result
of an electrical shock from 110 or 220 volt sources.

Injuries from electric shock account for about 1000 deaths annually in
the United States and comprise about 5% of admissions to burn centres.
More than 60% of reported electrical injuries are due to electrocution
with 110- or 220-V current and most commonly result from failure to
ground tools or appliances properly or from using electrical devices
near water. Electrocution is the fifth leading cause of fatal
occupational injuries in the United States; 1% of household accidental
deaths are caused by electrical injuries.

The spectrum of clinical injury from accidental electrical shock ranges
from a transient unpleasant sensation after exposure to low-intensity
current to sudden death due to cardiac arrest. Clinical manifestations
are sometimes seen immediately after contact, but might not become
apparent until several hours after injury.

Source: Fish R. "Electric Shock. Part I: physics and pathophysiology",
Journal of Emergency Medicine, 1993, vol. 11, pp. 309-12.

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

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
 
D

Doug Miller

Jan 1, 1970
0
You are correct; 100ma is about the lethal threashold. But it is difficult
to get 100ma off 120v unless you are in saltwater.

Guess again, bozo.


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

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
 
D

Doug Miller

Jan 1, 1970
0
I haven't found the time to work on the cord. I will now.

Someone please explain why do some modern factory drills, grinders
and saws get away without a ground plug?

They're double-insulated. That means it takes *two* failures to make the case
live, instead of one.
(Here's an ignorant question) Is it true that I can receive a fatal shock if
I touch my skin from either neutral or hot and then ground? If so, then why
not replace the ground with a safer model which doesn't allow a shock?

If you mean, can you get a fatal shock from touching either hot or neutral,
while some other part of your body is touching ground, the answer is - Yes,
you can.

Equipment ground conductors are intended to ensure that no matter what happens
in the device you're using, its chassis cannot become live because the chassis
is connected to a true earth ground.

For maximum safety, use grounded tools, and plug them into a GFCI.
Lastly, a hot or neutral short to ground shuts down my entire electrical
system. Is this the GFCI?

The *entire* electrical system? Every circuit? That's a bit unusual... that
would suggest that your main breakers have tripped.

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

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
 
R

Robatoy

Jan 1, 1970
0
don't remember the exact numbers, but seems like it was around the 90-100
milliamp range that was lethal due to causing fibrillation.
You are correct; 100ma is about the lethal threashold. But it is difficult
to get 100ma off 120v unless you are in saltwater.
Naturally adverse medical conditions, or just plain bad luck, will change
everything![/QUOTE]

Where do you get this ? You state this stuff as fact? Do you have ANY
idea how irresponsible you are?

Shame on you!
 
D

Doug Miller

Jan 1, 1970
0
You won't get much of a shock by simultaneously touching neutral and ground.

Not necessarily so. It depends on how well you're grounded. If you touch
neutral and ground simultaneously, your body is providing an alternate path to
ground, in parallel with the neutral conductor. If you're standing in a puddle
on a bare concrete floor, you're providing a fairly low-impedance path to
ground. I wouldn't want to try the experiment.

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

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?
 
D

Don Bruder

Jan 1, 1970
0
LRod said:
Neither of you are (the only one). I do, too. It's too easy to check,
and the potential consequences of not checking are too high.

Absolutely. The exact same concept applies to guns: "If there's even the
slightest doubt about whether it could be loaded, then *IT IS* until
proven otherwise."

If there's even the slightest doubt that a pair of wires might be hot,
then *THEY ARE* until proven otherwise.

Any other assumption in either case is stupidity on a scale you only
read newspaper articles about. Usually articles ending "Services will be
provided by <insert name> funeral home."
 
N

Nog

Jan 1, 1970
0
Norman D. Crow said:
IT ISN'T THE VOLTAGE! When I was in USN, they had studies showing deaths
from relatively low voltages. It's the amps, or more precisely the
milliamps, and where they travel. A certain milliamp current can be lethal
if it passes through the heart/chest area because it will cause the heart
to go into fibrillation, while a relatively high current may just cause
the heart to stop, but once it is removed the heart will restart on it's
own. I don't remember the exact numbers, but seems like it was around the
90-100 milliamp range that was lethal due to causing fibrillation.

In low voltage the injuries are not usually from the electricity but the
secondary reaction. If you are on a ladder and have an electrical induced
muscle contraction it can throw you off the ladder killing you when you hit
the ground. Likewise if you are holding a screwdriver, you might stab
yourself in the eye/brain. (has happened) You could twitch and drill a hole
in your leg. If it's an electric chain saw .....Did you ever see a chain saw
injury? It gets right to the arteries and you bleed to death fast.
So a properly grounded power tool is safer and a GFI plug is better.
 
T

toller

Jan 1, 1970
0
Robatoy said:
You are correct; 100ma is about the lethal threashold. But it is
difficult
to get 100ma off 120v unless you are in saltwater.
Naturally adverse medical conditions, or just plain bad luck, will change
everything!

Where do you get this ? You state this stuff as fact? Do you have ANY
idea how irresponsible you are?
[/QUOTE]
Any electrical book. Ever read one?
Electricians used to test for hot wires by touching it; a little tingle and
it was hot. Thats all it is, a little tingle. Certainly not a recommended
method with modern test equipment available, but not all that dangerous
since they used to get plenty of tingles.
Measure your resistance,and then figure out the associated current. It is a
lot closer to 0ma than to 100ma.
 
T

toller

Jan 1, 1970
0
Nog said:
In low voltage the injuries are not usually from the electricity but the
secondary reaction. If you are on a ladder and have an electrical induced
muscle contraction it can throw you off the ladder killing you when you
hit the ground. Likewise if you are holding a screwdriver, you might stab
yourself in the eye/brain. (has happened) You could twitch and drill a
hole in your leg. If it's an electric chain saw .....Did you ever see a
chain saw injury? It gets right to the arteries and you bleed to death
fast.
So a properly grounded power tool is safer and a GFI plug is better.
Even I can't argue with that...
I just get annoyed by the guys warning about the dangers of electrocution.
 
T

toller

Jan 1, 1970
0
Tim Zimmer said:
I haven't found the time to work on the cord. I will now.

Someone please explain why do some modern factory drills, grinders
and saws get away without a ground plug?
They are double insulated. In normal use you should not be touching
anything that could be energized by a shorted hot.
(Here's an ignorant question) Is it true that I can receive a fatal shock
if
I touch my skin from either neutral or hot and then ground? If so, then
why
not replace the ground with a safer model which doesn't allow a shock?

You cannot get a shock from a neutral unless it is open. A closed neutral
(which it would be, unless it were broken) is such a good conductor that
virtually no current would go through you. Until a few years ago dryers and
stoves had the frames connected to the neutral. They are perfectly safe
unless the neutral is broken, and then you may be the best path to ground.
Lastly, a hot or neutral short to ground shuts down my entire electrical
system. Is this the GFCI?

No, that is an overload that trips the breaker. It takes either time or a
huge overload. It protects the wiring, not you!
A GFCI trips very quickly if the current going out on the hot is not exactly
the same as the current returning on the neutral. It protects you if you
touch the hot. It will not protect you if you touch the hot and the
neutral; but you would have to be a real cluck to do that! (please refer to
my first post above.)
 
R

Robert Bonomi

Jan 1, 1970
0
I haven't found the time to work on the cord. I will now.

Someone please explain why do some modern factory drills, grinders
and saws get away without a ground plug?

Older style equipment has only one layer of insulation. A *single* failure
exposes the operator to electrical shock, unless the equipment is properly
grounded. With the grounding, it requires _two_ failures for possible
shock.

Newer gear is constructed in a style called "double insulated". It takes
_two_ separate "safety equipment" failures for the operator to be exposed
to a possible electrical shock.

By the nature of the 'double insulated" design, a failure of the second
insulation is much *less* likely than a failure of the 'grounding' system
in older equipment.

Hence safety is provided for in a "more reliable" manner. and the 'ground'
plug is not needed -- it doesn't provide any 'additional' protection.
(Here's an ignorant question) Is it true that I can receive a fatal shock if
I touch my skin from either neutral or hot and then ground?

Short answer: "Yes, you _can_ receive a fatal shock that way." This is not
to say that it _will_ be fatal in every instance. (see the 'long answer',
below, for all the gory details.)

Long answer (bear with me, it _does_ take a *long* discussion to cover all
the relevant matters) follows --

That's a *complicated* question. First off, what constitutes a "fatal"
shock depends on a _lot_ of things. The absolute minimal considerations
are 'how much _current_', and '*where* on the body'. applied directly
to heart muscle, a handful of milli-amps, which requires only a few volts,
is sufficient to cause 'catastrophic' problems.

Applied to the skin, away from the heart, what constitutes a 'dangerous'
level requires higher levels.

"How much" higher depends on a lot of things. The 'resistance' of skin,
etc. depends on a whole sh*tload of factors., but the biggest one is
how _dry_ the skin is, where contact is made. On a living being, "dry on
the surface" skin has a resistance of several thousand ohms. When skin is
damp -- sweaty, for one example -- the resistance decreases radically.
Can be as low as a few hundred ohms. _Below_ the surface of the body,
resistances are quite low. *especially* so for 'nerve fiber', which
runs *everywhere*.

Now, we have to take a digression into 'how electricity works'.
(note to purists: this description *is* somewhat simplified)

When you have two things "in parallel" connected to a source of electrical
power, There is always a flow of electric current through *both* of those
things. "How much" current flows through each thing is determined by the
resistance of that thing.

Note: 'in theory', "ground" is "ground", and is always at exactly the same
potential, regardless of location. In practice, it doesn't work that way.
"Ground" is a moderately lousy conductor, and you may get different levels
at different places.

In addition, the 'ground' and/or 'neutral' wires are *not* "perfect"
conductors. They are real-world devices, and have 'internal' resistance.
Depending on the size of the wire, and the length back to the transmission
point, this resistance can be significant. Any piece of wire, when you
connect to it at a point along its length, can be regarded as two resistors,
one representing the internal resistance from the beginning to where you
connect to it; the other from that connection-point to the other end of the
wire.

This means, among other things, that the 'neutral' wire _at_a_point_distant_
_from_the_power_source_, is *not* at the same 'ground' level as 'ground' at
the transmission point.

If you connect your body across the 'hot' wire, to ground (either 'earth
ground', or the 'ground' wire), you are placing yourself "in parallel"
with any other 'devices' (or 'loads') on that power feed. As those devices
have relatively high resistances (relative to 'just plain wire'), there
will be a considerable flow of current through your body.

If you connect your body across the 'neutral' wire, to ground (either 'earth
ground', or the 'ground' wire), you are placing yourself "in parallel" with
only the resistance of the 'return' part of that wire. This resistance is
comparatively _low_, and the current flow will be comparatively small.

From all this, it should be obvious that there is no simple nor easy means
of predicting "just how much" current _might_ flow through your body if you
get across the wires.

One more consideration to throw into the pot. There is no 'guarantee'
that the 'hot' and 'neutral' wires are _properly_ connected/identified.

What one _thinks_ is th 'neutral', may, in actuality, be the 'hot'.
It's not likely, but do you want to "bet your life" (literally!) on it?

The only "safe" way to work on electrical wiring is to:
0) assume that unprotected contact with the wiring *will* kill you.
(even if not _always_ true, you only get to be wrong ONCE )
1) disconnect it from the power supply
2) ensure that *nobody* can re-connect it without your OK.
(this is what "lock-outs" are for.)
3) test _after_ disconnecting to make sure there is no power present.
4) work on it *as*if* power was still present. (see rule #0)
(i.e. rubber gloves, insulated tools, only one wire at a time, etc.)

While that may _look_ excessively paranoid, it isn't.

Items 1,2,3 'appear' to describe a 'fool poof' system for ensuring safety.
Unfortunately,
"For every fool-proof system, there exists a *sufficiently*determined*
fool capable of breaking it."
applies.

that's why 4 *is* necessary.
If so, then why
not replace the ground with a safer model which doesn't allow a shock?

That's what modern "double insulated" tool design _does_.

That is *why* most tools are built that way today. <grin>

As for "doesn't allow a shock", well, the laws of physics are not subject
to repeal by the acts of man. ANY place there is a difference in electric
potential, there is the 'potential' for an electric shock. (Pun intended!)

The most one can do is engineer things so that getting a shock is "difficult".
Lastly, a hot or neutral short to ground shuts down my entire electrical
system. Is this the GFCI?

Probably. :)

GFCI detects _unbalanced_ current flow in the hot vs neutral wires.
This happens *only*if* there is 'some other path' for current to flow
through.

In the case of a 'hot to ground' short, assuming it is a true short (as
in approximately zero resistance), it will be a bit of a race between
the overload circuit breaker, and the GFCI, to see which trips first.

In the case of a 'neutral to ground' short, you do not have an 'overload'
condition, so the GFCI is the one shutting things down.
 
D

Don Kelly

Jan 1, 1970
0
Robatoy said:
You are correct; 100ma is about the lethal threashold. But it is difficult
to get 100ma off 120v unless you are in saltwater.
Naturally adverse medical conditions, or just plain bad luck, will change
everything!

Where do you get this ? You state this stuff as fact? Do you have ANY
idea how irresponsible you are?

Shame on you![/QUOTE]
-------
Actually, such information is available many places, including the EPRI book
on EHV power lines. The 100ma level is about the 0.5% probability level for
fibrillation. However, fibrillation is time dependent so that on prolonged
contact, the level drops (i.e. at a let-go current of 9-10ma it takes about
10 minutes to cause fibrillation). In many cases, design is based on a 5ma
level which is considered at or below the let-go level (not painless) for
both adults and children.
 
T

toller

Jan 1, 1970
0
Don Kelly said:
-------
Actually, such information is available many places, including the EPRI
book
on EHV power lines. The 100ma level is about the 0.5% probability level
for
fibrillation. However, fibrillation is time dependent so that on prolonged
contact, the level drops (i.e. at a let-go current of 9-10ma it takes
about
10 minutes to cause fibrillation). In many cases, design is based on a
5ma
level which is considered at or below the let-go level (not painless)
for
both adults and children.

For what contact time is that 0.5% figure for 100a? Or is it just an
average figure for all contacts?
 
N

Norman D. Crow

Jan 1, 1970
0
In low voltage the injuries are not usually from the electricity but the
secondary reaction. If you are on a ladder and have an electrical induced
muscle contraction it can throw you off the ladder killing you when you
hit the ground. Likewise if you are holding a screwdriver, you might stab
yourself in the eye/brain. (has happened) You could twitch and drill a
hole in your leg. If it's an electric chain saw .....Did you ever see a
chain saw injury? It gets right to the arteries and you bleed to death
fast.
So a properly grounded power tool is safer and a GFI plug is better.
I wasn't arguing the point that the cord should be replaced and the tool
properly grounded. I was merely making a comment about the fact that it
doesn't have to be a high voltage or high current that can kill you. There
are so many variables in an electric shock situation that it is nearly
impossible to set a hard & fast rule about what may or may not be fatal.

As Toller said, electricians often get "tingles". Not my idea of how to test
a circuit, but I've seen many USN electricians mates test circa WWII
shipboard fuse panels(cylindrical fuses on both hot & common) by walking two
fingers down the line of fuses. When they get a tingle across one fuse, it's
the bad one. Still not my idea of fun.
 
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