What you need is a UK EE to eplain it from the UK end.
So here goes…
The UK electricity supply suffers from a safety double whammy, our mains supply voltage to domestic premises (houses and light electrical load) is 220V which is very much more dangerous than 110V, but added to this, our frequency of supply 50Hz has a harmonic of 100Hz and this is also instrumental with interfering with muscle contraction.
Other supply frequencies cause muscle contraction issues, but unfortunately the heart has a particular sensitivity to our mains frequency.
Stoppage of the heart is by far the most likely route to death by electric shock, it is the fastest and requires the least amount of current to cause a fatal incident.
You can be killed by electric shock in other ways, such as arc envelopments, flash burns, or serious internal flash burns, but the heart death route is by far the most likely route.
It takes a certain amount of current to actually stop or interfere with muscles,-
actually it is the delivery of certain amount of electrical energy over a specified period of time that kills (or Joules per second = watts just like on the medical programs with the heart defibrillators)
As you will know
Current = voltage divided by resistance (I+V/R)
So when you look at electrical safety, (and since one can only hazard a guess at what resistance will be during an electrical shock - due to many factors), it is obvious that the greater the voltage, the greater the amount of current, and hence the greater amount of energy delivered within a given period of time.
What I’m saying here is that the UK system is inherently more dangerous that the US one, and so more serious precautions have to be taken.
When you look at any electrical power supply, there are a number of cables that carry current all the time, but in the UK we have one that appears to do nothing.
This is connected to ground, and for our purposes we call it earth. The truth is, it is actually connected to a common point and the blue neutral wire is connected here also, its just not obvious to non-electrical types.
The differance is that neutral carries away the current supplied by the live wire, and returns it to the source, earth wire carries no current under non fault conditions.
If the neutral wire becomes damaged, or bared, there is very little risk to the user.(it takes fairly unusual circumstances to make neutral a hazard)
The earth wire is connected to any metal parts of the appliance that are not intended to carry current, and which the user is likely to touch, such as the chassis.
If a fault develops, where the case becomes in contact with the live wire, this dangerous voltage will be passed straight down the earth wire and to the source of supply, this is a short circuit and as a result a very large current will flow.
The current will be so large, it will very rapidly blow the fuse or trip out any safety device.
The absolute and most critical point to bear in mind is this,
The resistance of the earth path to the source of supply is designed to be very very much lower than any possible path through your body to the source of supply
This means that there should not ever be the chance for you to get a shock between live supply and earth and this is the most common way of getting a shock.
Unfortunately if you were crazy enough to open an electrical appliance and you get a shock between two parts of the circuit that are supposed to have the voltage on them, you are in serious difficulty unless there is additional protection such as a power breaker(Residual current device RCD)
There are other ways to reduce the risk, the most obvious is not to have an electrical supply in an area where hazards such as water exist, and in a bathroom a wet human is likely to have a much lower electrical resistance and hance be much more vulnerable.
The shutters in our sockets are there because we have to protect children and the inherently stupid from our potentially lethal electrical system.(I know of one old girl who used a metal handle table knife to lever out plugs from sockets :eek: )
You will also have noticed that our plug prongs are much larger than most anywhere else, this allows for better electrical connections with less resistance, and this helps in reducing nny resistance in the earth path, again, for electrical safety, and also, large prongs can dissipate more heat and so we can use those plugs to run appliances which use more current.
If a US socket were rated at 13Amp and a UK socket is also rated at 13Amp, the UK socket will deliver twice as much power because the mains voltage is also twice as high.
We in the UK are somewhat paranoid about electrical safety, our standards are very high, some might argue too high, but then, idiots abound over here so maybe we have the right idea.
In the US the 110V system is intended for light electrical loads, I doubt that you would want to run say a cooker on 110V as you would need a large current flow to provide the power, and this would need very large cables, where we in the UK can get away with perhaps 6mm cable(I still use 10mm), you would need at least 12mm cable and possibly as much as 20mm cable to carry the current that would have the same heating effect (basically you would need twice as much current on 100V as on 220V)
I think you will find that US domestic supplies have circuits for this purpose, and that large installed appliances like cookers have a 220v supply available.
I can think of a couple of ways of doing this, you can have a domestic supply that is fed from 3 wires, from a transformer, which is centre tapped.
The centre tap is the return line for either of the two 110v feeders, and if you want 220V then you connect across the two 110v feeders.
Even with this US arrangement it is inherently safer than the UK, because you are most likely going to get a shock between one of the 110V feeders and return and most unlikely to get a shock by being connected somehow to both 110V feeders.
Having our system of earth connection has some advantages, because modern circuit breakers work very reliably in such a configuration, and they trip out bery quickly indeed.
The US version of the power breaker used to be voltage operated compared to our current operated breakers, ours tend to be very much more sensitive and trip out at lower fault currents.