Hi, I am rewiring my house, or a large part of it at any rate. If I
turn off the MCB for a radial circuit, is there any chance I can get a
shock from the neutral? (I know that there are no other connections to
the radial circuit, but also that the MCB only isolates the live.)
Also, I stupidly bought 2 X 100m reels of 2.5twin / earth cable in
local RS store. Its the wrong colour for Ireland - Red and Black
cores. If any of you good folk ever visit Dublin it's going for a
song, or a pint or two. ;-)
Because, if other appliances are running on other circuits, they create a
lower resistance path to neutral, which then causes the neutral to have a
higher potential than earth. So, in which case, if you touch yourself
across neutral and earth, then the higher potential in the neutral will flow
through you to reach earth, and you will say OUCH ! and drop whatever tool
you have in your hand, onto your foot. Then you'll have three points of
pain on your body, one where the electricity entered, one where the
electricity exited and a sore foot.
Hope this explains it a bit better.
A differing opinion:
Yes, if the installation is wired incorrectly.
No, if it is wired correctly. In the circumstances BW describes the max diff
between any earth & any neutral anywhere in the house at any
combination of min/max load should be less than 5V, not really much of a
In my own house I will happily work with just the MCB off, after checking L,
N & E with a meter, but would hesitate in a strange house.
As I think someone else advised, touching N to E on your 'turned off' (not
isolated :) circuit will trip the RCD (if you have one) in the consumer unit.
Gravity-sensitive ones. On a network-wiring training course attended by
a distant colleague, the "instructor" seriously claimed that propagation
speed in twisted-pair cable was faster vertically than horizontally.
(It was a bizarre misunderstanding based on a grain of truth, as it turned
out: network-premises types use "vertical" to mean "backbone", and
"horizontal" to mean "final run out to individual desktop" - think
multi-storey buildings and it makes sense. And since you might use
fibre or gigabit links in the backbone, but plain old 10BaseT out to
individual network ports, the instructor had construced an alternative
universe in which the physical orientation of cable made a difference to
the speed of signal propagation. An extreme case of "a little knowledge"...)
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