There is no isolator switch between the main inlet and the fuse board. I
need to turn the power off to rewire a ring. I understand one has to pull
the main fuse out of the inlet. How does one do this without zapping
Your fuse box or Consumer Unit should have a Main Switch. You should be able
to rewire a ring to your fuse box by turning the main switch on the fuse box
to OFF. You only need to pull the main fuse out to change the fuse box.
The only fuse before the consumer unit is the distribution company fuse
- which will be held into its carrier with tamperproof seals, the same
as the meter.
Provided that you are very, very careful - the main switch in the "fuse
box", plus using insulated tools, should give you all the protection you
need from being "zapped".
However, should you decide to break the seals, provided the mains
switch(es) are all off and the meter isn't showing that power is being
consumed, then removing the main fuse shouldn't be any more "exciting"
than pulling a mains plug from a wall socket. There will be no current
flowing through it and the voltage is "only" 240v.
The "exciting" bit happens later - if you have made even a very simple
wiring error and plug the fuse back in with a fault in place. That can
get *very* exciting, with a great risk of flash, fire, shock, death,
house burnt down, etc.
If you don't know how to thoroughly test a ring main to ensure that it
is safe, then you really shouldn't be going anywhere near the main fuse.
I cannot over-emphasise how dangerous it is to plug it in, with a
house wiring fault present. A *huge* current can flow, vapourising the
copper contacts on the fuse holder instantly and sending it out as a
conductive plasma at a temperature of over a thousand degrees. Your hand
is likely to be at the centre of that...
Surely not. When you plug the fuse back in, the wire in it will blow -
that is what the fuse is for after all. Anyway, the main switch in the
consumer unit will be OFF at this point.
I hear stories of electricity board meter readers getting funny about
the broken seal but I have never heard of anybody getting done for it.
Electricians fitting consumer units routinely break the seal.
I have fitted some consumer units LIVE but I would not recommend it.
The safest way to do it is to screw a 2 pole junction box near the
meter output, and transfer the meter output leads to that, very very
carefully. It needs insulated wire cutters (and preferably gloves) to
cut the tails while they are live. Cut one wire and terminate it in
the junction box, then cut the other one and terminate it in the
junction box. After you have terminated both meter tails in the
junction box, you can play around as you wish with the consumer unit -
it's all dead.
Then you have a final exciting bit which is to connect the tails
coming out of the new consumer unit to the junction box. Again,
insulated tools and gloves.
The above is strictly for those who really know what they are doing
with electrics. Done correctly, it's perfectly safe.
Nowadays, unfortunately, a DIY consumer unit installation is probably
illegal and breaking the seal is going to draw attention to it having
been done. This creates an incentive to do the installation live,
using the junction box method. And using WHITE cable of course - you
can still buy the stuff in certain trade outlets ;)
There is nothing to stop the individual attempting to plug the fuse back
in, with the mains switch on. A simple "mistake". Especially if the
"ON/OFF" plate by the main switch hasn't been replaced..
However, there is nothing to stop an individual temporarily disconnecing
the incomers in the consumer unit, to make things easier. Then wiring
that up incorrectly.
The fuse *will* blow - once it has had a large enough current flowing
through it for long enough. However, pushing a fuse carrier in by hand
is a relatively slow process. It will pass through a phase with a
significant amount of resistance between contacts. Which, in fault
conditions, can generate a great deal of heat and light.. and that
energy released in a small space will vapourise a lot of copper..
That would be the least of the OP's worries - if he attempted to push
the main fuse back in with a dead short in the consumer unit..
So why mention it as a possibility? It is not something to even mention
to an untrained DIY'er.
<snip description of something only trained and experienced people
Agreed. But, anyone that has to ask how to do it doesn't meet that
requirement. So why mention it?
Just a bit of playing devil's advocate here but surely if you're going
to attempt to replace said fuse all you'd have to do is check the
voltage between the two ends of the fuse carrier before attempting to
replace. If you've been an idiot and directly connected live and
neutral/earth somewhere in the house it'll show mains voltage.
Just my 2p :)
You miss the point. If the person knows enough to make safety tests -
then there is no problem.
However, someone who has to ask almost certainly doesn't know enough.
DIY house wiring in general is potentially dangerous enough - but, for
most mistakes the protection devices will do their job and limit the
effects. The DIY'er stands a good chance of learning from the mistake.
However, mess with the main fuse......
Indeed.... I've done various things with electrics and have got by
without much experience but with a good understanding of basic circuits
and the differences between earth, neutral and live.... plus a bit of
caution, a dollop of common sense and a healthy respect for the results
of getting it wrong :)
While we're on this subject, does anyone know of a good web page that
describes the Part P rules? I've tried looking for that before but
failed to come away with many concrete facts from the point of view of a
Interesting table. Why don't they also prohibit wearing black
underpants - it would be as enforceable. Can't even wire up a garden
shed, under these regs.
My earlier comment about using white cable (still available trade) is
that if you do the job in that, it looks like it pre-dates the regs
and isn't going to get picked up on a check.
On Mon, 10 Mar 2008 22:52:51 +0000, ARWadworth wrote:
=================================If the wiring is the WHITE he means then it has no particular
significance. My wiring has a mixture of white and grey although it's
predominantly grey, and it all pre-dates Part P. I got the impression he
meant white tails.
Using Ubuntu Linux
Actually, sticking a test lead probe (of the type most people
will have at home) into a main fuse carrier is a really bad
idea. A slip, or the meter on the wrong setting, and you could
easily be engulfed in an arc flash which would be extremely
disfiguring, if not eventually fatal.
[email address is not usable -- followup in the newsgroup]
Not very likely I agree. But I saw the mess someone tampering with a meter
made of his hand. He also could not see for 3 days.
If the OP wants to remove the fuse (assuming there is only one) then you
turn the main switch at the CU off, cut the seals on the fuse and pull it
out. Good practice would then mean you check the supply is dead as vary
rarely the fuse may be on the neutral side.
=================================Buy an isolating switch (try http://www.tlc-direct.co.uk /) and get your
supplier to connect new meter tails to it. You can then fit your own tails
from the new isolating switch to the consumer unit. Subsequent work will
only need the isolator to be switched off.
Using Ubuntu Linux
As has already been posted you should have no need to remove the Main fuse
however instalations vary and incomming cables are of many types .To remove
a main fuse can take quite a tug ,sometimes this can loosen the whole board
and in the worst case fracture the incomming cable.(this has happened I have
a colege who has the burn scars to prove it).
As for the quote 'it's only 240v' be warned 240v IS LETHAL .It is not the
voltage that will kill you it's the current (amps) IIR 6-8 milli amps to
stop the heart.
Finally I think it is still a criminal offence to tamper with electricity
company equipment and the main fuse and meter come into this category that
is why they are sealed.
Yes I know most people ignore this fact but if you have an accident trying
to remove the main fuse you are to blame.
My advice is to ring your supplier and ask them to fit new tails to a
seperat 100a DP switch as already posted.
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