Earths can be dangerous

[trader_4]

And we all saw that towering inferno where about a hundred died that used flammable siding. There is where do as you please gets you.

[Jimmy Wilkinson Knife]

How is that a problem? The case could be not connected to anything, and the power could be isolated from ground. If one side of the power touched the casing, nothing would happen, as it would have no desire to go to ground. What causes the danger is because live wants to go to ground, through you.

[Rod Speed]

Because when a fault shows up in one of those, there will be no indication of a fault at all and the protection that nothing earthed used to provide is now gone. So you no longer have any protection, and that is over the entire collection of houses etc that are powered from that transformer in the substation if you don?t have individual transformers for each house.

Yes, but with those devices that have other grounds likely present via the water pipes etc, you now have a problem that the case is at mains voltage and touching that and the ground simultaneously and that can certain kill you with that in separate hands as is most likely in that situation.

And that can happen post fault when the fault produces no visible effects and the device keeps working and there are other grounds available.

[Jimmy Wilkinson Knife]

How can a phone possibly give you an electric shock? It's plastic.

[Jimmy Wilkinson Knife]

Oh dear, you've fallen for the media hype again. Millions of people don't get killed (which are of course no use to journalists), and a few do, and you think everyone's in danger.

[Cursitor Doom]

But earth-referencing power lines is not without its dangers either:

[Rod Speed]

Cursitor Doom wrote

Those distribution systems arent earth referenced.

This is a much better example of the downsides of earth referenced systems.

[Jimmy Wilkinson Knife]

You're talking about the output from a say 1kV low current power supply.= =

So one of those outputs touches the supply line, so what? How is that =

going to want to go to anywhere but the other side of that power supply'= s =

output?

[Jimmy Wilkinson Knife]

Funny how it jumped to earth then.

What is this "open circuit neutral" stuff? I have live and neutral coming into my house form the transformer over the road (for the yanks, there's only 0 and 240V here, no 120 - Australia is the same I think). If the neutral got disconnected, I'd simply have no power, nothing would work in the house.

[Jimmy Wilkinson Knife]

I think I know where you're going with this: you're saying since neutral and earth are identical, that a disconnection of my neutral from the substation means current flows through my appliances from live to the house neutral (now disconnected from the supply), which is also the same as the house earth, so earthed house appliances and taps get some voltage as current passes through the ground to get back to the substation. Yip, agreed - you get stupid things happeneing with grounded supplies. It's an insane idea and everything should be floating.

[Rod Speed]

That voltage is normally 11KV and it isnt low current either.

We arent talking about one of those touching the supply line, we are talking about a fault in one of the heater elements in an appliance earthing one side of the floating supply.

It earths one of the supply rails and does that completely silently with a floating supply, wont even blow a fuse.

And then, when anyone gets between a supply line and earth, they get electrocuted and since that is quite likely to see the current go thru their body because what is in contact with the supply line is usually a different arm or foot to what is in contact with the earth, high risk of dying.

And an RCD can't protect that individual in that situation.

[Rod Speed]

Doesn't have to be earth referenced to do that with 440KV or 330KV that that line is.

There is no longer a neutral connection, so the return current goes thru the earth and that is a MENS system.

Yes, I know I should have said 'that is a MENS' but that isnt as likely to be understood.

And in that case there was no longer a neutral.

That's what the 'open circuit' bit means.

Yes, but its certain to be MENS here.

That's not correct, the return would be via the earth.

We also have quite a bit of SWER, which is single wire earth return with just one wire going to the premises, usually farms where its much cheaper to have just one wire when the run of wire can be a considerable distance, fraction of a mile or more.;

[Rod Speed]

Yep, and that can kill you because when the neutral goes open circuit, there are no symptoms that that has happened, so you can get killed or very seriously injured when you grab a metal water tap to turn the hose off when standing on the wet ground near it or with bare feet in the bathroom etc.

And you do with floating supplys too, and that is over the entire area supplied from the distribution transformer, not just the one house.

Trouble is that that needs a transformer for atleast every house.

[trader_4]

There is no reason several houses cannot be on the same transformer with an ungrounded system. It has nothing to do with whether it's one house or three. You could do it right now, just remove the earth ground at the transformer and at the three houses.

[Jimmy Wilkinson Knife]

:

A high voltage bench supply (I've got one here) won't provide current to= =

ground. The current must flow between the two HV outputs. Let's say =

something goes wrong and the +ve 2kV connects onto the live input, how d= o =

you think that would make it want to go to ground? To complete the =

circuit it must go to the -ve output of the 2kV PSU, which is still =

floating.

[Jimmy Wilkinson Knife]

=

So I have 240V between a pair of wires, fed from a transformer. My =

neighbour shares this transformer and does what? Raises one of those to= =

lines to 1000V above ground? How would he manage that by mistake? Even= =

if he did, it's not going to affect me unless I also have a fault (eg an= =

appliance with a short to its chassis).

[tony sayer]

In article , Jimmy Wilkinson Knife scribeth thus

No its not a stupid idea. The problem is that if you do have a floating supply a fault with leakage to ground can make the supply no longer float.

At least with the present supply set up its a known that one side is referenced to earth and with RCD protection in line it does work very well. Of course anyone connecting themselves to Live and Neutral will defeat the purpose of the RCD.

However to do that is quite a deliberate act most all shocks are accidental connection of the live line because of the way the RCD detects the current flow unbalance it trips very rapidly disconnecting the supply thus preventing the user from harm.

Furthermore as it monitors the current flows an unwanted leakage to earth will rapidly be detected and bought to the householders attention.

Can anyone name a country in say Europe who feeds domestic power on a floating supply anywhere?..

[trader_4]

How about just a country anywhere?

[Jimmy Wilkinson Knife]

So I was right then, floating voltages are safer.

No use if the appliance cord can reach to the bath.

It almost never will.

Funny thing is, we have all these silly rules, yet they sell legal double sockets that have a 20A limit, yet you can plug two 13A appliances into them without anything blowing. They claim it would never happen, but it does, and I've seen it.

[Rod Speed]

Nope, they are in fact still earthed, not floating.

It cant.

It does in fact happen with everyone. Everyone has their hot water heater element fail and their oven element too..

They don't claim it will never happen. They know it will work fine.