analogy of 'safety voltage partnership'
Discussion
If you were to look at the number of people electrocuted in their homes each year then there surely would be a good reason to lower the voltage of the electricity supply in our homes.
at 240 volts, 1 in 10 people touching a live conductor die (or not, there must be some statistics somewhere that can be enterpreted in such a way as to prove this), at 120 volts almost everyone lives.
So we enforce a lower voltage, and statistically more people live who touch live conductors. However, now the voltage is halved, you need twice the current, which means the wires under the floorboards get 4 times as hot, which means you get more house fires and more people die.
Should kids be sticking their fingers in a toaster in the first place?, were the fires caused by dodgey wiring which is therefore not the fault of the SVP?
There's a point I'm trying to make here, not sure exactly what it is, or if I've come across well.
Oh well.
at 240 volts, 1 in 10 people touching a live conductor die (or not, there must be some statistics somewhere that can be enterpreted in such a way as to prove this), at 120 volts almost everyone lives.
So we enforce a lower voltage, and statistically more people live who touch live conductors. However, now the voltage is halved, you need twice the current, which means the wires under the floorboards get 4 times as hot, which means you get more house fires and more people die.
Should kids be sticking their fingers in a toaster in the first place?, were the fires caused by dodgey wiring which is therefore not the fault of the SVP?
There's a point I'm trying to make here, not sure exactly what it is, or if I've come across well.
Oh well.
bryan35 said:
If you were to look at the number of people electrocuted in their homes each year then there surely would be a good reason to lower the voltage of the electricity supply in our homes.
at 240 volts, 1 in 10 people touching a live conductor die (or not, there must be some statistics somewhere that can be enterpreted in such a way as to prove this), at 120 volts almost everyone lives.
So we enforce a lower voltage, and statistically more people live who touch live conductors. However, now the voltage is halved, you need twice the current, which means the wires under the floorboards get 4 times as hot, which means you get more house fires and more people die.
Should kids be sticking their fingers in a toaster in the first place?, were the fires caused by dodgey wiring which is therefore not the fault of the SVP?
There's a point I'm trying to make here, not sure exactly what it is, or if I've come across well.
Oh well.
Hi bryan
If I understand you correctly, you are trying to say that the focus on speed per se to reduce accidents/KSI's is not getting to the root cause of the problem. The drivers education needs to be such that they drive safely under all conditions and know when/when not to increase their speed. Putting up cameras is doing nothing to educate drivers; like the kid in your illustration who puts his finger in the toaster. It doesnt matter what you do with the voltage (speed limits ) the person concerned must be educated how to behave. Is this what you meant?
A good analogy, but perhaps a better one is the excellent "Height Kills" on the ABD website...
www.abd.org.uk/ht-kills.htm
www.abd.org.uk/ht-kills.htm
Mr E said:
Anyway, makes no sense from a electrical point of view.
V=IR
So as you correctly say, halve the voltage, double the amps for the same power.
As your 'R' is constant, you're still going to get zapped.
In terms of receiving shocks, remember that the "r" of a human body remains constant (about 2500 ohms from hand to hand), so the current flow is proportional to the voltage applied.
Thus if you connect yourself to 250V about 100mA will flow which is plenty enough to kill you, especially when it is AC. At 110V only about 45mA will flow through you, which is usually survivable.
At higher voltages the "kick" effect tends to save you. If you touch something high voltage the muscular jolt it gives you tends to throw you off so violently that it often prevents fatal injury.
If you wanted to pick an "ideal" voltage from the point of view of killing the casual receiver of shocks, 240v is pretty much the one to go for...
bryan35 said:
80v is quite nasty,
especially at 17 Hz.
Add into that a bucket of water, a packet of table salt, a set of jump leads, a radiator, a wet sponge and some gaffer tape, and you've got yourself a 'confession assistance machine'
RF shocks are another VERY nasty type.
bryan35
You should work for the SCP with this mean streak
AC is less dangerous than DC as there is less of a "lock-on" effect (where you can't let go)... The most dangerous range is around 6-700V DC as used on third rail electrification.
One of my mates once shorted the mains through his body and blew a 5A fuse without any ill effects.
Lower voltage doesn't necessarily mean safer. Wiring practices and the like have an effect too. I did some Googling on American domestic wiring a while back to help an American pigeon rescuer with a domestic wiring problem and some of the stuff I found made my hair stand on end.
One of my mates once shorted the mains through his body and blew a 5A fuse without any ill effects.
Lower voltage doesn't necessarily mean safer. Wiring practices and the like have an effect too. I did some Googling on American domestic wiring a while back to help an American pigeon rescuer with a domestic wiring problem and some of the stuff I found made my hair stand on end.
BlackStuff said:
At higher voltages the "kick" effect tends to save you. If you touch something high voltage the muscular jolt it gives you tends to throw you off so violently that it often prevents fatal injury.
I suppose someone is going to say that this is the same analogy as if you hack down the motorway at 240kph, it keeps you awake because any incident gives you such a jolt. 110 kph you drop asleep.
Or have I got the wrong end of the stick?
WILL SOMEBODY THINK OF THE TOASTER'S Pigeon said:
Lower voltage doesn't necessarily mean safer. Wiring practices and the like have an effect too. I did some Googling on American domestic wiring a while back to help an American pigeon rescuer with a domestic wiring problem and some of the stuff I found made my hair stand on end.
I read a message on another BBS about US wiring standards. They commented that they were surprised that any houses in the US are still standing what with the wiring colour standards, wire nuts, staples, non-shuttered socket, non-sleeved plugs, unearthed sockets...
Gareth
[quote=bryan35]If you were to look at the number of people electrocuted in their homes each year then there surely would be a good reason to lower the voltage of the electricity supply in our homes.
Reply - ignoring analogies to motoring.
1/ I understand the US 110 volt system was chosen (ie 110v) as the highest voltage unlikely to kill.
2/ Just as with 6 v car systems instead of 12, half the voltage means double the current for the same power - and FOUR TIMES the heat in the cables - or 4 double the diameter for the same heat.
The REAL answer to electric shocks is ECBs Earth Circuit Leakage Breakers which work like this:
Under all normal conditions the current that flows out of the power lead is identical to the current that flows back through the neutral (return) lead.
Only when current "leaks" from the live lead to some sort of fault - like a human body - are the out and return currents different - and with modern electronics very small differences can be detected instantly and trip off the safety switch before the anyone gets anything more than a slight tingle.
My house built in 1979 had one built in from new, covering all circuits - and in 23 years it has tripped more than once - thank goodness. You can buy ECBs to plug in to any part of the system esp for lawnmowers etc for £10 to £20 or so - never mow a lawn without one
BETTER STILL Have one fitted to the mains where it comes into the house so that it covers ALL outlets
Idris
Reply - ignoring analogies to motoring.
1/ I understand the US 110 volt system was chosen (ie 110v) as the highest voltage unlikely to kill.
2/ Just as with 6 v car systems instead of 12, half the voltage means double the current for the same power - and FOUR TIMES the heat in the cables - or 4 double the diameter for the same heat.
The REAL answer to electric shocks is ECBs Earth Circuit Leakage Breakers which work like this:
Under all normal conditions the current that flows out of the power lead is identical to the current that flows back through the neutral (return) lead.
Only when current "leaks" from the live lead to some sort of fault - like a human body - are the out and return currents different - and with modern electronics very small differences can be detected instantly and trip off the safety switch before the anyone gets anything more than a slight tingle.
My house built in 1979 had one built in from new, covering all circuits - and in 23 years it has tripped more than once - thank goodness. You can buy ECBs to plug in to any part of the system esp for lawnmowers etc for £10 to £20 or so - never mow a lawn without one
BETTER STILL Have one fitted to the mains where it comes into the house so that it covers ALL outlets
Idris
[quote]BETTER STILL Have one fitted to the mains where it comes into the house so that it covers ALL outlets
[/quote]
No Just fit them to the circuits that have portable appliances pluged in and outside the equipotinsionaly [spelling]bonded zone, This is usualy outside
If you have them on ALL circuits the lights go out when you toast some frozen bread due to the damp bread causing a fault in the toaster
[/quote]
No Just fit them to the circuits that have portable appliances pluged in and outside the equipotinsionaly [spelling]bonded zone, This is usualy outside
If you have them on ALL circuits the lights go out when you toast some frozen bread due to the damp bread causing a fault in the toaster
nonegreen said:
As I understand it 32mA and below is the safe current. Anything above that is pottentially lethal.
That's about the size of it, which is why RCDs usually trip at 30mA of leakage.
Picking up an earlier point, the notion of a human body tripping a 5A fuse is urban myth I'm afraid! With a resistance of about 2500 ohms you would need to apply 12500V to get 5 amps to flow. And of course, 5A won't blow a 5A fuse, as that's actually the rating of the current it is designed to carry safely. To get a conventional fuse to blow would typically take 2 to 3 times its rating so therefore you'd need to be connected to at least 25kV to get a 5A fuse to blow! Not very likely in a domestic house...
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