Circular saw won't ground, safe?

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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?
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wrote in message

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.)

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Completely false. You *can* get a shock from a neutral that is not open, if you provide a good enough alternate, parallel path to ground. And dryers and stoves with the frames connected to neutral are *not* safe - that's why the NEC now prohibits that on new installations.
-- 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?
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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. <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".

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.
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wrote:

(I'm posting from Europe, your local terms may be different).
All electrical appliances must be insulated, meaning that the live and neutral feeds are not connected to any accessible part of the appliance. However things break, and so we must also design them to be moderately safe even after this insulation fails.
One way it to wrap them in a conducting case and then earth this case. If they're supplied through an appropriate fuse, then the fault current (internal "works" to case) is then enough to blow the fuse and make the appliance safe. For this reason the earth must not only conduct, but it must conduct _well_.
Another approach is an RCD or GFCI. This measures "earth leakage", usually be measuring the difference in current between live and neutral wires. If there's a difference of more than a few mA (i.e. the current has gone _somewhere_ it's not meant to), then something is wrong and the RCD trips.
UK wiring has much better appliance fusing than other systems, so until quite recently (10-20 years) we've been quite lax about using RCDs. US wiring is a shocking abomination by design and so it's only the huge number of GFCIs and arcing-fault breakers (a totally alien concept in the UK) that stop your evil aluminum wiring killing the population of Detroit weekly.
Around the late '60s, a new approach developed. Plastic was the new thing, and plastic cased appliances were everywhere. These allowed the economic use of "double insulated" appliances. They were still insulated (of course) but now they also had to _remain_ insulated, even after an internal fault. If the wire fell out of the switch and hit the case, the case mustn't in turn become "live". Of course with plastics for cases, this isn't that hard to arrange. Once the standards had got sorted out and clever designers knew how to work with them, you could even get such bizarre things as double-insulated hair curlers, where you stick a big metal heating element on your head, without an earth wire. Not something _I'm_ going to trust in a hurry, I can tell you.
You can spot double insulated appliances in Europe by the two nested squares logo. It's also likely that they only have two wire cables, as you describe. The crucial thing is their internal design though, not merely missing off the earth wire!
--
Cats have nine lives, which is why they rarely post to Usenet.

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On Mon, 16 May 2005 14:17:00 +0100, Andy Dingley

[good stuff snipped]

Andy, Andy, Andy. You were doing good until here.
GFCIs are primarily protection when you're near water (kitchen, bathroom, spa, pool, basement). They're not used on every circuit.
Arcing fault breakers are a relatively recent development, and I suspect, the result of arc fault breaker industry lobbying rather than a solution to an actual widespread problem. I'd be interested in knowing how many deaths AFIs could have saved in the century of the Edison system that we didn't have them.
Aluminum wiring (in house) was used for a relatively short time, in only a very few houses (comparitvely), quite a number of years ago (on the order of 30 or more). Although there are probably some houses that still have it, it's not mowing down the populace left and right. The vast, VAST majority of US homes are wired in copper.
Aluminum feeders and transmission lines are an altogether different story and aren't killing anyone because they're aluminum, so far as I know.
[more good stuff snipped]
--
LRod

Master Woodbutcher and seasoned termite
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