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On a standard electrical outlet, one in three of the holes is live (the
other two being neutral and ground). A child who inserts a metal
object into a random hole thus has about a 33% chance of receiving
an electrical shock.
If you added extra holes to the outlet, and perhaps decorated them
with bright colors to draw a child's attention to them, it would
increase the odds that a given hole would be safe. You could also
have the extra holes trigger a piercing alarm to act as a form of
negative reinforcement, as well as alerting any adults in the vicinity.
Sure, some unlucky kids might still get a shock, but no system is
perfect, and it's easier than mucking about with safety covers that
have to be actively replaced (and might be a choking hazard
anyway).
Why not make the extra holes live, too?
http://www.artlebed...verything/rozetkus/
The advantage of a two-prong plug. Comes in a wall mounted variation too. Yay! [mitxela, Aug 21 2013]
The Metal Melter
http://www.youtube....watch?v=GCrqLlz8Ee0
These videos have great content but really world class production value and pacing. Like an episode of Mythbusters rolled into 5 minutes. [bungston, Aug 23 2013]
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I'm pretty sure all household circuits are now
required to have RCDs, meaning that children are
free to safely poke whatever they want into
sockets. |
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Morealso, sockets have shields on the live on
neutral holes which are slid aside by the insertion
of the earth pin, making it hard for a child to poke
something into the live hole. |
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In other words, you seem to be solving a problem
which hasn't existed for a decade or more... |
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// You could also have the extra holes trigger a piercing
alarm to act as a form of negative reinforcement // |
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Only slightly less effective a deterrent than electrocution. |
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//A child who inserts a metal object into a random hole thus has about a 33% chance of receiving an electrical shock. |
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If you added extra holes to the outlet, and perhaps decorated them with bright colors to draw a child's attention to them, it would increase the odds that a given hole would be safe.// |
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I suggest that all electrical outlets be replaced by a new 1-pin variant. |
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When I was 2 our house had child safety covers on all the
outlets. I wanted to plug something in so I got a knife and
started prying off the safety cover. Of course my mom saw
this and thought I was trying to stick the knife in the
outlet. </tangent> |
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/sockets have shields/ true in the colonies as well? I
have not seen this. We have relatively safer 120V
house lines of course. |
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Electrical sockets are little more than two primitive
vertical slots in many of the colonies. These are sometimes
to be found with twigs protruding from their inner
confines, because the natives have mistakenly believed
that they can somehow precharge the twigs, then store
them batteries like to make fire on subsequent camping
trips. |
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That's ridiculous. Everyone over here knows that you can't
start a fire
by sticking little slivers of wood into electric sockets. |
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We do it to keep faeries out of the house. |
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See now I'm no sparkamatrician, but I think you're confusing the term "neutral" and thinking that means it's safe. Because it isn't. The neutral can be live too, quite easily in fact. Don't touch it. |
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I like the idea of the socket shields that [Max] described - this colony certainly doesn't have these as standard. |
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Yeah, American outlets don't have any sort of cover. I've seen some marketed as
“safety” outlets that have a built-in cover that only retracts if both prongs are inserted
simultaneously, but I don't know how well they work, and they're certainly the
exception, not the norm. Also, the RCD (known in the U.S. as a GFI or GFCI outlet) is
generally only used in wet locations like kitchens and bathrooms. Most residential outlets
do not in fact have them. Regardless, the GFI doesn't completely prevent a shock, but
only limits its severity and duration. And a malfunctioning GFI may provide no protection at all. |
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//The neutral can be live too, quite easily in fact.// |
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Well… no, it can't. Not in a properly wired outlet. And if it's improperly wired, there are
only really three possibilities for which the neutral line could be hot:
1) Hot and neutral reversed — except then, the hot line is neutral, and you still have the
same probability of being shocked
2) Neutral line wired to same phase as hot line — in this case, since the potential
between the neutral and hot lines is zero, the outlet won't work.
3) Neutral line wired to opposite phase as hot line — if this has somehow happened,
you've got a 240 volt outlet instead of a 120, and anything you plug into it will pretty
much explode.
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If you were to open the outlet up, sever the neutral wire, and grab hold of both ends,
then you might get a shock from the return current of some other device on the line.
Likewise, if you somehow managed to reduce your resistance to ground to less than that
of the neutral line (I'm hard pressed to imagine how you could do this though—maybe if
you were soaking wet, standing on a grounded metal plate, and stuck your tongue in the
outlet) you might get a shock. But you shouldn't ever get shocked by simply sticking a
metal object into the neutral line. If you do, there is something seriously wrong with the
outlet wiring. |
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Would it not be possible to wire up a socket (I'm thinking UK 3-pin type) that has a very low current on the neutral wire, on the ground wire is a solenoid that trips to allow full power on the live wire. |
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That way, at least three knives and a bit of wire will be needed to get a shock. |
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//Yeah, American outlets don't have any sort of
cover.// Well, then, there's the problem and the
solution. UK sockets, and the corresponding
plugs, and the requirement for RCDs on new
installations, provide a mechanically and
electrically robust system which is extremely safe,
even at the standard 220V. The higher voltage
also reduces the bulk needed for cables or,
conversely, allows the socket to provide more
power. |
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All in all, then, the corrrect answer the the
problem is to adopt the better standard for
domestic electrical wiring. Adding distractional
holes to sockets is inelegant. |
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I believe that most states in the US now require self
covering sockets, either everywhere or below a
certain height. Of course this would only be evident
in new construction, which is a small percentage of
the housing stocks. |
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The US aftermarket is certainly flooded with self-covering
sockets and receptacle plates. I have a healthy selection of
them carefully laid out on my kitchen table this afternoon. |
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//there are only really three possibilities for which the neutral line could be hot:
// |
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...Well as I said I'm no electrician, and I'm nervous to engage you on your own ground, but what about if the neutral connection back at the junction box or power line was poor? |
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//Likewise, if you somehow managed to reduce your resistance to ground to less than that of the neutral line (I'm hard pressed to imagine how you could do this though—maybe if you were soaking wet, standing on a grounded metal plate, and stuck your tongue in the outlet) you might get a shock.// |
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This is in direct violation of parallel circuit theory. I don't need to have less resistance to ground than the neutral line. I need to have enough of a percentage of the conductance of the neutral line in order to carry sufficient current to interfere with my nervous system, say 30mA or above. This is very different. Getting return-path shock during welding is a good example of this. The bulk of the current is running back through the steel structure, but I get just enough going through me that I get banged nonetheless. |
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//This is in direct violation of parallel circuit theory.
I don't need to have less
resistance to ground than the neutral line. I need to
have enough of a percentage
of the conductance of the neutral line in order to
carry sufficient current to
interfere with my nervous system, say 30mA or
above. This is very different.// |
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You're arguing semantics. Okay, I should have said
“close to” instead of “less
than”, but the difference between the two is hardly
substantial. |
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The average human body has a resistance of between
300 and 1,000 ohms—let's go
with the low figure. Your standard neutral run has a
resistance from the wall plate
to ground of less than 0.2 ohms (likely less than half
that, but let's go with that
number for demonstration purposes). So assuming you
have a current of 20 amps on
the circuit, that translates to a load resistance of
about 6 ohms (assuming a 120
volt supply). This means that the voltage on the
neutral line is about 4 volts. 4
volts / 300 ohms is about 13mA. |
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13mA is a fairly substantial amount of current,
enough that you'd certainly notice
anyway (especially with AC). But it would hardly be
fatal, going by your 30mA
threshold. |
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Remember also that we're making a lot of
assumptions here: that you have an
exceptionally high current on the line (most breakers
trip at 15 or 20 amps), your
body's resistance is on the low end of the scale, and
you're standing on a grounded
steel plate. But if your body resistance is on the
higher range, or the current on the
line isn't running close to the maximum for the circuit
breaker, or if you're standing
on an insulator (such as, say, the wood floor of your
house), or you're wearing
shoes, or you're pretty much not trying very hard to
deliberately get shocked by
the neutral line, you don't really need to worry too
much. |
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Which brings me to your earlier question: |
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//what about if the neutral connection back at the
junction box or power line was
poor?// |
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It would have to be a really, really bad connection.
So bad that the circuit probably
wouldn't even work. Let's assume that the neutral
connection has a resistance of 2
ohms. This would mean that, in the example of the
device given above that had a
load of 6 ohms, it would only have a voltage drop of
90 volts, which probably
wouldn't be enough for it to function. Even if it did,
you're looking at a voltage of
30 volts on the neutral line, which with 2 ohms of
resistance yields 450 watts of
power dissipation. Most likely, your house would burn
down. |
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So realistically, by the time the resistance on the
neutral line got up high enough
that the return current flowing through your body
would be substantial enough to
harm you, you'd notice something was seriously wrong
with the line. Generally
speaking, problems with the neutral wire produce
substantial enough effects that
the last thing you have to worry about is being
shocked by accidentally touching it. |
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Stupid to put sockets at ground level, anyway... just at
the right height to be noticed by inquisitive bundles of
joy. I put them at lightswitch height in the nursery
building.
Residual current safety devices only reduce the
'chance' of fibrillation. |
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Cool, thanks for taking me through your logic. I yield to your superior knowledge. |
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I wonder how the numbers work out for return-path welding shocks then.... I've been hit so fricken hard when holding plates that I was definitely doing some current sharing. |
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Well, remember that with welding, we're talking
about 20 or more amps at 240v (which is equivalent
to 40+ amps at 110v). Even a tiny fraction of that is
going to be pretty substantial. Also, since the entire
point of using a welder is to inject current directly
into a steel plate, most of the safety features of an
electrical outlet don't really exist. |
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Note, however, that you did not die as a result of
these shocks. That's because even though they may
have been fairly substantial, they were still below the
threshold where they might be fatal. So if even that
sort of shock isn't deadly, you're not exactly going to get a life threatening jolt out of the neutral line
of your standard wall socket. |
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Au contraire, mon frere, it's very rare to find a welding
machine that puts
more than 45V through the stinger. Amperages, however,
can get quite high; I've run a 24V wire-feeder at close to
600a. |
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This makes getting lifted painful but very rarely deadly,
unless you have a pacemaker. I've been zapped more times
than I could possibly count, as has just about any
professional welder. It's rarely worse than brushing against
an electric fence, but it definitely gets your attention. It's
worst in the rain. |
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That's a good point—the other reason why welding
shocks aren't deadly is because the working voltage is
so low. (I was referring to the source voltage and
current—although they technically work out to be the
same amount of power whether you measure at the
source or the welding tip.) |
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When you're dealing with a grounded steel plate, the
voltage doesn't need to be very high in order to
produce substantial amperage (a theoretical
resistance of zero ohms would yield infinite amps at
any given voltage). So a welding torch, while more
likely to give you a shock than an outlet (due to the
lack of any sort of safety mechanisms), is actually
less dangerous if you are shocked. |
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But again, remember that we're only talking about a
few volts at the most between your average properly
wired neutral line and the ground. Touching the hot
line, of course, would be a whole different story.
Don't do that. |
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Getting lifted* while welding is usually the result of haste
on the part of the welder; you're hurrying to finish a job,
maybe you have a hole in your glove or your sweat has
soaked through, and your finger strays down and brushes
the electrode just as you shift your weight and put your
knee down on the ground clamp... Zap! |
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I've gotten about 400a from my left hand across to my right
knee and it didn't harm me at all, though it was highly
unpleasant and--I'm not making this up--it made my fillings
buzz. |
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* a high-amperage electric shock can cause violent muscle
spasms, making you involuntarily jump up or jerk away
from the ground point. It feels a little like you're levitating,
thus the welder's parlance 'getting lifted'. |
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So the conclusion here is that everywhere get a
sensible electrical system. The UK standard
polarized, grounded, fused and shielded plug and
socket system being infinitely superior to the
slapdash interim methods used in the colonies. |
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It's also much more civilized when your lamp doesn't
dim every time the iron's heating element kicks in. |
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Ha! You should try 100v Japan, in one place the cooker wouldn't even get hot enough to cook a pancake.. |
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//The UK standard ... being infinitely superior to the
slapdash interim methods used in the colonies.// |
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Tell that to your feet when you step on one. |
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[-] for discouraging a healthy spirit of enquiry amongst the young of your species. |
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//Tell that to your feet when you step on one// |
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When you've experienced such pain, it lends
perspective and precludes whining about "the store
not having the good creamer I like". |
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// Tell that to your feet when you step on one // |
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Ahhh, Upturned Plug Syndrome .... the terror that haunts the dark hours. |
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I wonder if the law requiring plug covers in the UK has to do with a greater interest in putting butter knives in plugs. I found that plausible. |
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I will link a fine video by the unfortunately monikered "King of Random" in which he demonstrates his very low voltage, high amperage "Metal Melter". His videos are great and very instructive. |
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//law requiring plug covers in the UK// It's not a
cover as such. It's just a little plastic upside-down
T-shaped shutter thing inside the socket. The
cross of the T covers the live and neutral holes. |
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On the plug, the earth pin is longer than the
others; this not only ensures that the first
connection is to earth, but it also allows the earth
pin to push the shutter aside and give access to
the live and neutral holes. |
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It probably adds 5p to the cost of an electrical
socket. |
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American and continental European electrical
hardware is very primitive and, from an English
perspective, not really fit for porpoises. Even the
Germans, who are normally quite good at
engineering, don't seem to get it right. |
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Perhaps the dangerous system commonly in use in the US has made for better parenting negating a big push for the safety devices in use elsewhere.
Like " Put that screwdriver back in yer toolbox Billy and grab yore gun. we're goin' huntin' " |
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That is perhaps because Britain's first stab at it was
rather unfortunate. This design represents at least
version 3.0, whereas America is still horsing around
with 1.43b, having not had the sh&t bombed out of
our infrastructure in some massive misunderstanding
of world domination by the same clan that brought
you 220V. |
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Does the US still allow electricians to work on live
circuits? I found that one of the most disturbing
things about the whole country. |
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In US industry there is a workplace safety philosophy that
revolves largely around the difference between 'allow' and
'ignore'. |
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//In US industry there is a workplace safety
philosophy that revolves largely around the
difference between 'allow' and 'ignore'// |
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Ha! That's true of lab work too. I was genuinely
shocked to discover there were actual safety rules,
guidelines and so on. From observation, you'd come
to the assumption we're making it up as we go along. |
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//Does the US still allow electricians to work on live
circuits? I found that one of the most disturbing
things about the whole country.// Probably safe
enough at 110V, or with RCDs, or indeed with a little
common sense. |
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If all safety rules were adhered to in the US the worker would be 100% safe but wouldn't be able to get close enough to the work to do the job. |
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// Does the US still allow electricians to work on live circuits? // |
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In many jurisdictions, 5000V live working is far from uncommon - but appropriate special equipment and training is required. |
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Then again, anyone who knowingly works on a 5kV system without proper training and equipment probably has a death wish anyway. |
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It is possible to work on overhead transmission lines at even higher volatges - up to 250kV and more - subject to the correct procedures being followed. Failiure to correctly follow procedures tends to elicit something a bit more serious (amd final) than a dressing-down by the foreman. |
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// I found that one of the most disturbing things about the whole country. // |
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You didn't look very far, did you ? That remark bespeaks a lack of imagination, a lack of perception, or most likely both. |
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I do routinely stick my hands in a 220V control
box, and have in the past done so in a 480.
The thing is, I'm the engineer, so I get to ignore
the safety rules some times in order to make the
stupid thing work. |
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The same goes for maintenance people, the
theory being that they're well enough trained to
make the right decisions. |
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The average worker is not, which is why said 220V
portions are all behind guard panels when the
system is in the field. |
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This thread reminds me of the three primary rules of
safety when dealing with engineers in your life: |
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1. Never let a E.E. wire your house.
2. Never let a Computer Engineer near your
computer.
3. Never let an M.E. work on your car. |
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Yep, because that's not their job or what they're trained for. |
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Similarly, never let a nonengineer design or certify anything. We all should play to our strengths... |
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