On Fri, 11 Aug 2017 22:15:45 +0100
Wols Lists <antlists(a)youngman.org.uk> wrote:
On 07/08/17 22:02, Carlos E. R. wrote:
On 2017-08-07 19:43, Paul Groves wrote:
So unless something is causing some other type of
the earth? Out earth connection is via the Neutral cable coming
into the building.
I don't understand this sentence. You don't have a separate ground
wire, instead you use the neutral cable?
The building doesn't have it's own ground pole, a metal rod inserted
into the earth?
I'm not familiar with the British electricity code. I guess it will
be different! :-p
For a domestic building we have single-phase 230V supply - NOT 240V as
many brits believe! The European standard is 230V, and we moved to the
standard maybe 20 years ago? (The standard says that the deviation
permitted goes up to the old UK 240V, and down to other countries' old
210V or 220V, so all appliances must be able to cope with everything,
but the supply is supposed to be 230V.)
Well, yes and no. The standard is harmonised as you say and equipment
manufactured now must be able to deal with the limits. But the voltage
supplied depends on the distribution transformers and those are
replaced as it becomes necessary, not just because there was a European
harmonisation. That's why the tolerance band in the standard is so
large. So in some places in the UK the nominal supply voltage is still
240 V just as in some places on the continent it is still 220 V.
Neutral is bonded to ground AT THE SUBSTATION (to the
best of my
knowledge). All of our electrics are 3-wire, live, neutral and ground,
with ground usually bonded - in the house - to the domestic water
system. Sounds dangerous until you realise pipes are mostly copper so
it's actually a massive electrical sink, and pretty safe. Dunno how it
changes things now we're moving to plastic pipes, but I'd have thought
it doesn't actually make much difference. Water is a conductor.
Again, yes and no. Most houses are supplied by an underground supply
that includes live, neutral and CPC (earth), grounded as you say at the
source. But some houses, mostly a lot of those supplied by overhead
wires, only have two incoming wires - live and neutral. The neutral is
earthed at the supply and in some cases is fed to the house as both
neutral and earth. In other cases it is fed only as neutral and the
consumer must provide their own earth using a ground spike.
Bonding to the water pipe is still very common but is not strictly
necessary in the now very common case that the incoming water main is
plastic. Bonding of metal taps etc is also no longer required.
For more detail see:
The other thing is, ALL modern domestic wiring runs
breakers, with an earth leakage trip. And these things are damn
sensitive. 30mA leaking to earth, and the inbound supply trips, taking
out the entire house electrical supply. So if you cut through your
electric lawn mower's cable, you won't get a shock. Everybody in the
house will, though, as the trip takes out all power!
It's not true that all circuits run through RCDs (residual current
devices), which replaced earth leakage circuit breakers. Some circuits
have to be protected and others can be. Alarm circuits are an example of
a circuit that some people do not believe should be connected through an
RCD (in case of a faulty RCD interfering with the alarm).
That's why, in a previous house, I had
super-sensitive socket trips
fitted in the conservatory - 5mA - so that a garden accident wouldn't
take the house out.
And all sockets are L/N/E with safety blocks - there's a safety plate
that prevents access to live or neutral, until the plug's long earth
pin pushes it out of the way. If your appliance doesn't have an
earth, the cable still needs a non-functional earth pin in order to
allow you to plug it in.
I remember a guy on Groklaw - who knew a bit about electrics - being
horrified by the french system where they have both L/N/E and L/N
sockets - and apparently you can put an L/N/E plug into an L/N socket
(sounds dangerous!), but not an L/N plug into an L/N/E socket (where's
the harm in that?). Apparently it's perfectly safe, for other reasons,
but that's well weird to us brits.
I don't think that's true but I'll let a French person respond.
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