Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 27/07/2010 18:05:59
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A friend of mine was going to use a metal knife to free some stuck toast from the toaster. He’s always been told this is a huge no, no, but he said it would all be fine because he had rubber-soled shoes on. So is it true that rubber-soled shoes will protect you from an electric shock?
Asked by Clive Pounds
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Dave: - I think the simple answer is it is possible they would protect you from an electric shock, but it’s not something I would ever recommend because it’s only “possible”. If you have a big, thick rubber sole then you're quite insulated from the ground, and if there’s no path for electricity to flow through, you won't get a big current going through you, so you'll be fine. It’s essentially a similar reason to why birds can sit on an electricity cable. They might be sitting on a very high voltage, but there’s no path for electricity to get down to earth through them so they’re absolutely fine, there’s no current flowing.
So, as long as you're just standing on your shoes you're not touching anything else, your feet aren’t wet so they're not creating a short path around the rubber soles to the ground, and you're not accidentally touching anything metallic - If you were touching the outside of a toaster which might be earthed then you might get a horrible current going through the knife, up your arm, then down the other arm, then you might be okay. But there’s so many things that could possibly go wrong, so unplug the toaster first.
Ben: - I think that sounds like a sound advice, and that by and large, don't stick metal things in electrical appliances.
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It depends which way the electrical current is travelling. Insulating footwear can help to reduce the shock to ground if one hand is touching a live wire. However if the other hand is holding the metal body of a earthed toaster they will not help you because the current will pas from one hand to the other via the heart. This is the most dangerous sort of electric shock. Electricians who regularly have to work on live wiring using insulated tools are taught to always keep one hand in their pocket when working live and only use one hand to work with to avoid this risk.
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I agree with Soul Surfer. A current flowing from one arm to the other is extremely dangerous, even if your feet are well insulated from ground.
BTW - here's a question:
All other things being equal, are the conditions in the UK potentially twice, or four times, as lethal as they are in the US (because of the difference in line voltage).
EDIT: Please don't answer that! I will start another topic.
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I think the toaster electrics are separated isolated from the case which leaves it at a floating potential not ground, there is no third prong for grounding the case.
You may experience a tingle not a heavy shock
Once a ground is established the circuit is complete to kick you across the room.
Still, I agree with you both, safe measure unplug the unknown.
Here is a spine tingler video
I grabbed a still of this huge toaster just to get your attention
[ Invalid Attachment ]
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Tommy,
There used to be a third prong tying the "dead" metal in the toaster to ground in the UK. I suspect that is still the case.
(no pun intended [:)])
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Tommy,
There used to be a third prong tying the "dead" metal in the toaster to ground in the UK. I suspect that is still the case.
(no pun intended [:)])
Ooh ok, thanks, I did not know this. Dismiss my comment on that due to lack of exposure.
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Tommy,
I think your comment is quite correct with respect to the US.
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Tommy,
I think your comment is quite correct with respect to the US.
Thanks Geezer, I guess since most of the subject threads that are global, I should indicate and addressed them in an orderly fashion, to avoid this type of future confusion. I am still climbing that learning curve. [:I]
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I am still climbing that learning curve.
I hope that's why many of us post on this site. If we really knew all the answers, what would be the point? The nice thing about TNS is that there is a cross-section of people interacting with each other that have all kinds of different bits of knowledge. That does not tend to happen too often in science and technology.
Consequently, if we can establish ways to communicate with each other effectively, we all stand to learn a lot.
Anyway, that's my take on it.
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I am still climbing that learning curve.
I hope that's why many of us post on this site. If we really knew all the answers, what would be the point? The nice thing about TNS is that there is a cross-section of people interacting with each other that have all kinds of different bits of knowledge. That does not tend to happen too often in science and technology.
Consequently, if we can establish ways to communicate with each other effectively, we all stand to learn a lot.
Anyway, that's my take on it.
Food for thought Geezer...
The coin's edge is the third side of the coin and it is continuous, rarely landed on...
AaH yes! Star Trex's, The Borg?
The collective promotes numerical identity at the same time, extinguishes individuality, but Hue can have 7 of 9!
We lose variety, the spice of life.
Isn't that something, efficient communications we have, but communicating efficiently is at a lose.
In some cases, gain in equal knowledge mixed with choice can be a double edged sword, in some cases.
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Yes this type shoes are best to save you form electric shock this shoes is important when you are working with electricity if you have no so you can use other have shoes like tennis shoes, golf shoes and other big shoes actually shoes are use so your foot can't touch the earth if you are working without any shoes or your foot touch to earth so current can pass from your body to earth that's why you can use any shoes through which current can;t pass like rubber and wood etc
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There used to be a third prong tying the "dead" metal in the toaster to ground in the UK. I suspect that is still the case.
I think your comment is quite correct with respect to the US.
Many years ago, I designed and received approval for mains-powered electronic equipment in North America and Australia, and the regulations were somewhat different. At that time, UL (originally the fire Underwriters Laboratories) were in the process of harmonising their standards with IEC (International Electrotechnical Commission), so they will be much more aligned today. But you can't entirely escape from the history...
My impression of the history is as follows:
- A large part of the early battle in North America in the 1880s was between Edison (promoting DC power) and Westinghouse (promoting Tesla's 3-phase AC power)
- There was a long debate over the safety of the two systems, including killing animals and humans (in the electric chair)
- Eventually AC won out - it was simply more efficient for transmission
See: https://en.wikipedia.org/wiki/War_of_the_currents
- But this emphasis on safety meant that the USA was saddled with a 110V AC system, which won't necessarily kill you, but it has high resistance losses
- In the early days, electrical insulation was not very good, using things like rubber, which perishes over time, creating a fire risk
- Since the 1890s, UL have provided safety certification of equipment in the USA. They preferred to have equipment encased in metal, to reduce the chance of fires. They were not so worried about risks of electrocution.
- And the traditional US power plug had only two pins. One of which was indirectly connected to earth, but you couldn't trust which one.
The perception of electrical safety was not made such an advertising war in the rest of the world - electricity is obviously dangerous, so don't touch it! (IEC classifies anything above around 32V AC as potentially dangerous)
- Europe went with a 240V electrical system, which has lower resistance losses, and requires less copper*
- But 240V requires much better insulation and/or a good connection to ground as an electrical safety barrier.
- That's why many European power plugs have a third wire as a connection to Earth
- So the European standards, which were unified under the IEC favoured "Double Insulation" (two independent layers of insulation, each able to survive 240V + switching surges). Most of our electronic appliances today use this philosophy, and are acceptable around the world.
- This causes problems for devices like toasters, as common insulators can't stand the high temperatures involved (when I was a child, the toaster used fragile sheets of mica rock as the insulator holding the hot filament!).
- So the common toaster in 240V countries has an earthed metal case. If you are holding this metal case while probing the interior with a metal implement, you will create an electrical path from one arm holding the knife to the other arm holding the toaster case - a potentially lethal situation.
- There are some other factors at play:
- Your knife is likely to touch the element and the metal guides for the toast, blowing the fuse
- Modern electrical codes require a residual current device, which will detect this imbalanced current flow, and cut off the electricity before it permanently kills you.. See https://en.wikipedia.org/wiki/Residual-current_device
Summary: Do not probe the internals of electrical devices with the power on!
Even probing equipment with the power off could damage insulation, making the appliance unsafe for future use...
- *Other countries had to decide what electrical standards to use; Australia followed UK practices at the time; Japan went with US equipment on the East coast, and European equipment on the West coast, with unfortunate consequences for their power grid after the Fukushima tsunami on the East coast.
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That's why many European power plugs have a third wire as a connection to Earth
- So the European standards, which were unified under the IEC favoured "Double Insulation" (two independent layers of insulation, each able to survive 240V + switching surges). Most of our electronic appliances today use this philosophy, and are acceptable around the world.
If you have double insulation, you don't need an earth connector.
Double insulated equipment has only 2 wires in the lead.
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It doesn't matter if it is 1V or 1 million Volts, all electricity can be potentially lethal, as it isn't actually the voltage that kills you, hence why people struck by lightning can survive. Its the Amps that kill you and as little as 1A can stop the human heart. Mind you 1A is not a huge amount, but if you have a weaker heart it is still enough to get the job done.
So lets say your body has 1 Ohm of resistance to it (it doesn't and most peoples bodies are in mega Ohms of resistance, but use 1 Ohm to show you the dangers of it).
Now Watts Law states it take 1V to push 1A through 1 Ohm of resistance.
So if you body is 1 Ohm, and your power source is either 110V or 220V, that means there could be a potential of 109A or 219A pushed through your body, and if so little as 1A can stop your heart with that type of Amperage you BBQ your heart good.
Too many people are wrong when they talk about electrical, Volts=Pressure, Amps=Current not the other way around and its because too many people can't be bothered to know the difference is why so many people are hurt or killed every year due to accidents because they are mislead by inaccurate information, which is shocking (hehe) considering this information is easily accessible using Google.
A high enough voltage though and regular shoes will not protect you from becoming grounded and getting shocked, the higher and higher the voltage climbs the greater the chance the current can actually jump (arc) to ground through you. Think of it the same way static electricity arcs/sparks or how lightning is able to jump such huge distances.
Ultimately just play it safe, don't take unneeded risks as much as it may save you a few minutes to not be safe, the price you pay of your life is simply not worth it.
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isn't actually the voltage that kills you, .... Its the Amps that kill you
AArgh!
Why do people keep saying that?
You can't have one without the other- it's called Ohm's law.
Now Watts Law states it take 1V to push 1A through 1 Ohm of resistance.
No.
It's Ohm's law
So if you body is 1 Ohm, and your power source is either 110V or 220V, that means there could be a potential of 109A or 219A pushed through your body,
It's not a potential (the potential is 110 or 220 V) It's a current
And it would be 220A or 110 A rather than 219 or 109.
Also, it's very unlikely that any practical path through the body has such a low resistance.
On the other hand
as little as 1A can stop the human heart.
Much less current than that will stop the heart. Even as little as 0.001 Amps can do it- if there's a direct connection.
More commonly as little as 0.03A would kill you if it was going through teh heart.
Too many people are wrong when they talk about electrical,
Yep.