In addition to not having a metal case, they are double insulated..
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.
No Jim
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=2E....." moment and its another one for the books. This sounds like a pertinent case:
Richard
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.
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?
-- 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?
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?
They're double-insulated. That means it takes *two* failures to make the case live, instead of one.
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.
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?
Where do you get this ? You state this stuff as fact? Do you have ANY idea how irresponsible you are?
Shame on you!
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?
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 funeral home."
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.
No doubt.
I've been an electrician for over 30 years and I can tell you it is possible to get killed on 120V, but it is generally considered to be the current that kills. As little as 100mA will cause the heart to fibrillate regardless of voltage. It depends on the victims age, thickness of skin (callouses insulate somewhat), how dry the skin is and where the contact points are on the body. One older fellow I worked with would routinely put his finger in light sockets to check for voltage. His skin was old, dry and calloused and the current only passed through his finger. Another who worked a circuit hot by lying on a piece of insulating cardboard under a house died because his sweaty neck touched a cold water pipe. Damp, thin skin, current through the brain. Not a good combination. GFI protection is a good thing and cheap insurance.
Old Sparky
toller wrote:
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.
Even I can't argue with that... I just get annoyed by the guys warning about the dangers of electrocution.
They are double insulated. In normal use you should not be touching anything that could be energized by a shorted hot.
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.
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.)
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.
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.
That's what modern "double insulated" tool design _does_.
That is *why* most tools are built that way today.
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".
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.
------- 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?
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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