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).-- ytk, Aug 20 2013 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=GCrqLlz8Ee0These 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] 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.
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.
In other words, you seem to be solving a problem which hasn't existed for a decade or more...-- MaxwellBuchanan, Aug 20 2013 // You could also have the extra holes trigger a piercing alarm to act as a form of negative reinforcement //
Only slightly less effective a deterrent than electrocution.-- Alterother, Aug 20 2013 //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.//
Good point.
I suggest that all electrical outlets be replaced by a new 1-pin variant.-- Wrongfellow, Aug 20 2013 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>-- DIYMatt, Aug 20 2013 /sockets have shields/ true in the colonies as well? I have not seen this. We have relatively safer 120V house lines of course.-- bungston, Aug 21 2013 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.-- xenzag, Aug 21 2013 That's ridiculous. Everyone over here knows that you can't start a fire by sticking little slivers of wood into electric sockets.
We do it to keep faeries out of the house.-- Alterother, Aug 21 2013 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.
I like the idea of the socket shields that [Max] described - this colony certainly doesn't have these as standard.-- Custardguts, Aug 21 2013 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.
//The neutral can be live too, quite easily in fact.//
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.
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.-- ytk, Aug 21 2013 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.
That way, at least three knives and a bit of wire will be needed to get a shock.-- not_morrison_rm, Aug 21 2013 //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.
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.-- MaxwellBuchanan, Aug 21 2013 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.-- MechE, Aug 21 2013 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.-- Alterother, Aug 21 2013 //there are only really three possibilities for which the neutral line could be hot: //
...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?
//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.//
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.-- Custardguts, Aug 21 2013 //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.//
You're arguing semantics. Okay, I should have said “close to” instead of “less than”, but the difference between the two is hardly substantial.
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.
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.
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.
Which brings me to your earlier question:
//what about if the neutral connection back at the junction box or power line was poor?//
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.
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.-- ytk, Aug 21 2013 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.-- Ling, Aug 22 2013 Cool, thanks for taking me through your logic. I yield to your superior knowledge.
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.-- Custardguts, Aug 22 2013 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.
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.-- ytk, Aug 22 2013 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.
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.-- Alterother, Aug 22 2013 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.)
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.
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.-- ytk, Aug 22 2013 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!
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.
* 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'.-- Alterother, Aug 22 2013 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.
It's also much more civilized when your lamp doesn't dim every time the iron's heating element kicks in.-- bs0u0155, Aug 22 2013 Ha! You should try 100v Japan, in one place the cooker wouldn't even get hot enough to cook a pancake..-- not_morrison_rm, Aug 22 2013 //The UK standard ... being infinitely superior to the slapdash interim methods used in the colonies.//
Basically, yes.-- MaxwellBuchanan, Aug 22 2013 Tell that to your feet when you step on one.-- RayfordSteele, Aug 23 2013 [-] for discouraging a healthy spirit of enquiry amongst the young of your species.-- 8th of 7, Aug 23 2013 //Tell that to your feet when you step on one//
When you've experienced such pain, it lends perspective and precludes whining about "the store not having the good creamer I like".-- bs0u0155, Aug 23 2013 // Tell that to your feet when you step on one //
Ahhh, Upturned Plug Syndrome .... the terror that haunts the dark hours.-- 8th of 7, Aug 23 2013 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.
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.-- bungston, Aug 23 2013 //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.
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.
It probably adds 5p to the cost of an electrical socket.
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.-- MaxwellBuchanan, Aug 23 2013 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' "-- cudgel, Aug 24 2013 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.-- RayfordSteele, Aug 24 2013 Does the US still allow electricians to work on live circuits? I found that one of the most disturbing things about the whole country.-- UnaBubba, Aug 24 2013 In US industry there is a workplace safety philosophy that revolves largely around the difference between 'allow' and 'ignore'.-- Alterother, Aug 24 2013 //In US industry there is a workplace safety philosophy that revolves largely around the difference between 'allow' and 'ignore'//
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.-- bs0u0155, Aug 24 2013 //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.-- MaxwellBuchanan, Aug 24 2013 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.-- cudgel, Aug 24 2013 // Does the US still allow electricians to work on live circuits? //
In many jurisdictions, 5000V live working is far from uncommon - but appropriate special equipment and training is required.
Then again, anyone who knowingly works on a 5kV system without proper training and equipment probably has a death wish anyway.
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.
// I found that one of the most disturbing things about the whole country. //
You didn't look very far, did you ? That remark bespeaks a lack of imagination, a lack of perception, or most likely both.-- 8th of 7, Aug 24 2013 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.
The same goes for maintenance people, the theory being that they're well enough trained to make the right decisions.
The average worker is not, which is why said 220V portions are all behind guard panels when the system is in the field.-- MechE, Aug 24 2013 This thread reminds me of the three primary rules of safety when dealing with engineers in your life:
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.-- RayfordSteele, Aug 25 2013 Yep, because that's not their job or what they're trained for.
Similarly, never let a nonengineer design or certify anything. We all should play to our strengths...-- Custardguts, Aug 25 2013 But it is our passion...-- RayfordSteele, Aug 26 2013 random, halfbakery