Firstly, I'd like to thank everyone who writes here. I've been doing
my first (and last) renovation over the last three years and the
advice here has been invaluable even though I've hardly had to post
I wonder if anyone can work out what's going on here:
I've just replaced plastic light switches with ones that have metal
faceplates, and I *just* can feel electricity when I brush my fingers
against them lightly. I'm certain it's not static -- I can feel the
It only happens on one lighting circuit; on other circuits with the
same new switches you can't feel anything.
Does this mean that the earth on that circuit isn't connected? Or
that it is connected and there's electricity flowing continuously to
earth due to a fault, a little of which diverts through me when I
touch the switches? Should I ignore it or try to fix? (The case of
my new laptop feels the same sometimes and the user's manual says it's
Any advice appreciated as always.
Likeliest cause is that the earth connector isn't connected to earth
somewhere further back than the switch, and that the 50Hz you can detect
is capacitively coupled into the free-floating earth conductor which is
correctly connected to the switch faceplate. You can check this out
if you have a multimeter - you should find that the resistance between
the faceplate and something-else-which-has-a-good-earth (e.g.: socket
screw, socket earth pin, outer case of a plugged-in non-double-insulated
metal appliance, etc.) is Huge, while the resistance from the faceplates
of the other, non-tingling faceplates to the same point is Negligible
(probably down at 0 ohms unless your meter has an accurate "low ohms"
range). Turn off the power to the lighting circuit while you do this -
less because of the risk of shock (you've shown the available current
at the suspect faceplate is not currently (ha) dangerous), but becuase
it'll louse up your resistance measurement.
But it *is* worth tracking down where the earth connection's missing,
since without an effective earth at your metal faceplate you (and those
who share the house) are at risk in the event of a "hard" fault where
the live directly comes into contact with the faceplate; at that point
what you want to happen is for a brief flash behind the faceplate and
the MCB/fuse for the lighting circuit to trip, EEBADS-style; *not* for
the faceplate to stay live, now with plenty of heart-stopping current
available, to give a nasty (or worse) belt to the victim.
Your previous installation - with plastic faceplates - masked the fault
I'm guessing you have; tens of years ago it wasn't even a requirement
for lighting circuits to have an earth-continuity conductor. Until you
fix the underlying fault (which you should do ASAP), replacing the
metal-faced switch with the previous plastic one is a Good Move - but is
no substitute for the proper fix, mind you...
(While your laptop might give you a similar weak tingle, we Presume it's
a double-insulated/Class-II design where any such current is restricted;
while the tingle you say you're getting suggests the absence of an
effective earth in an arrangement where such an earth *is* a
HTH - Stefek
Hmm, I'd wondered about posting a similar question, I've also replaced
some plastic face plates with metal ones and wondered what to do with
the earth cable - as it's currently connected to the original *plastic*
back plate. I can't feel any electricity, so I've left it as is now,
should I move the earth to the face plate - or will it make no
difference as it's only bolted to plastic anyway?
If it is a metal box, I thought it was there to earth the metal box. I'm
sure most of us don't turn off the ring to loosen face plates for
Mmm, stripping knifes touching the metal box.
We've had this out on the group a few times; the consensus, which I
share, is that it's (marginally) preferable to run the incoming cable(s)
to the earth terminal on the Accessory - if it has one - e.g. the
socket, fused-connection-unit, whatever - so that there's one fewer
connection to come adrift on the way to the "important" place, which is
whatever the socket/FCU/whatever feeds. A tail to the backbox is then a
better-than-relying-on-the-mounting-screws way to earth the backbox, and
earths the mounting screws for those rare designs where there's an
earthing terminal on the accessory which doesn't itself provide
continuity with the mounting screw surrounds.
For light-switches, things can be different - plastick plateswitches
don't have an earthing terminal, so parking the earth wires in the earth
terminal (usually) provided in the backbox is a sensible way to keep
it/them secure, and - if there are multiple cables, as there will be in
some wiring setups where all the joining's done at the switch positions
rather than in junction boxes and/or loop-in roses - does a "real"
electrical-continuity job. Metal-faced switches generally have an
earthing terminal - it's not simple to design them as
double-insulated/Class-II, as the mounting screws will earth the
faceplate when used with a metal backbox.
Ok - what would you do if there was no earth cable in the wiring and you
wanted to fit a metal face plate to a plastic backing box? The plastic
box does actually have an earth terminal in it - would you use a short
piece of wire from the backing plate to the plastic box (why?)?
Well as I don't know your layout I cant say exactly, but you should be
able to pick up the earth conductor somewhere and join a single to it. The
actual physical running is another matter and could involve a lot of extra
work, ie lifting floorboards, chasing out etc. You might if you were lucky
be able to feed a single conductor down the existing channeling. Very much
a suck it and see operation. Done it a few times and it can be a pain in
the a***. Costs the customer a lot of extra money!. One reason never to
cut off earth conductors, people do because they think they wont be needed
at a certain point, then again people are stupid.
If you're going to have to re-plaster, do the job properly and make sure
there's an earth throughout the lighting circuit in the normal way. If the
earth's been cut or left off, gawd knows what other bodges you'll find. If
it never was present, the wiring is old.
*I don't know what your problem is, but I'll bet it's hard to pronounce
Dave Plowman firstname.lastname@example.org London SW
I suspect this house has never been re-wired since it was built - late
1930s. The wiring is just 2 core in a grey round sheath, all the back
boxes are nasty grey plastic. Possibly upstairs has been re-wired with 3
core, but there's no obvious sign of re-plastering anywhere except the
hall, everywhere else is the original lathe and plaster.
Excuse my french - but what's a noggin? I'm going to run a single 1.0mm
earth wire to a socket down the edge of a door frame, all sheathed by
graan/yellow. Bit of a pain in the arse, but nothing compared to the
grief from the girlf of having a plastic socket in a house full of
A lath and plaster wall is hollow. It's constructed out of vertical studs.
But at perhaps two places there will be horizontal 'noggins' to add
strength and prevent twisting. These also stop you just dropping a cable
from top to bottom. But you can channel out over the noggin and bring the
cable round over it, then make good.
*It is easier to get older than it is to get wiser.
Dave Plowman email@example.com London SW
writes> >> Great advice here thanks - there is a nearby socket I can use for this,
Borrowing an earth connection from the socket circuit is against regs,
as its possible someone could one day disconnect the socket cct, but
leave the lights powered up. However, it will clearly greatly increase
the safety of your dodgy setup.
Uhoh. If its really that old, or even 40s or 50s, dangers are bound to
be lurking. The number 2 rule with really old wiring is dont move it,
not even slightly. A quarter inch of movement is enough to cause a
short or fire if the rubber's perished - and it normally is.
The number 1 rule? Disconnect it and rewire. 1930s wiring is anything
but safe: in fact 30s wiring in the condition it will be in today
would have been condemned even back in the 30s. I dont know when
lighting had to have earths, but 2 core lighting is very old, and
probably well past its reasonably safe by date.
I _really_ wouldnt want metal light switches on a dodgy setup like
that. Even when earthed, the level of shock protection is liable to be
real poor, and the odds of earthed things going live quite high. Why?
High earth impedances, wire fuses, no RCD, no crossbonding, no
earthing on parts of the install, heavily corroded wiring, high
probability of shorts, high leakage... no thank you. get it fixed.
Actually - none of the downstairs light switches have a cable for earth
(upstairs do). I guess I'm going to have to run a cable from the
switch/faceplate to a suitable earthing point - for instance central
heating copper pipe?
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