On Wed, 28 Jan 2004 13:36:41 +0000 (GMT), Dave Plowman
According to the regs, yes.
I did a bit of sub-contacting to a firm a few years back, before earth
bonding became daft. Being useless in every other aspect, (the firm,
not me), I was surprised when I went on a 2nd fix of a bathroom
extension to find a 4mm earth connected to anything in the room, the
shower and exposed metalwork as normal but also to the light fitting,
fan, shaver light, and anything else with a screew on it, whether it
could be touched or not. Everything in the room was double insulated,
bar the shower.
But you have to bond them 'even more'. The iee requires that it is
bonded. Even with the earth in the supply cable it is deemed to be of
too high a resistance.
Also as has been pointed out in some of the above threads the earth in
the circuit feeding the shaver socket is not neccesarily connected to
the exposed metalwork in the bathroom by means of other equipotential
and supplementary bonding.
On Wed, 28 Jan 2004 17:12:05 GMT, email@example.com (Lurch) wrote:
Interesting. I would love to see a proper estimate of the number of people
who come to grief(*) through situations involving the lack of kilometres of
4mm2 bonding cable, and how those situations arose, but then I am deeply
cynical by nature.
(*) Compared with, for example, the number of people who trip over their own
feet and fall down flights of stairs.
Extra credit: Define the universe and give three examples.
No-one said the regs made sense, or that they solved all common causes
of accidents in the home.
Some of it is excessive, some is required.
It is possible that in some instances such an excessive amount of
earthing would be completely OTT, but a blanket rule has to be applied
with the 'worst case scenario' being catered for. Not all electricians
seem to be able to do things safely when being told what to do as it
is, diy'ers would have trouble working out what was wanted and what
wasn't. Lazy people just wouldn't bother applying any safety rules at
all. Hang on, that's what happens now, none of this is compulsary,
it's just a guide.
If you buy a car with airbags you may not need them from a safety
point of view but they are fitted in most instances 'just in case'. A
similar rule is applied to safety measures in electrical
installations, they are there 'just in case' an accident occurs and to
minimise damage in the event that one does happen.
Not sure if you're agreeing or disagreeing with me, I'm sure it'll
come clear in a minute. Meanwhile:-
That's what I said. Connecting the metalwork in the bathroom together
is half the job, connecting all the other bits of metal in the
building together and also to a reliable earth point would be the
I have not yet come across 50Hz static.
I would be tempted to check that both sockets are properly earthed, both
the one you touched and the adjacent one. Checking that they are both at
the same potential with an ohm meter would be a good start. Try it on ac
volts first of all. It is not unheard of for earth wire to become
disconnected elsewhere in the circuit and this would not at first be
apparent as it would not stop appliances from working.
Best of luck and take care.
No chance. Static builds up to si high a voltage that even with several
megaohms in the path to earth, it discharges damn quickly, and won't give
any kind of "sustained 50Hz tingle" like wot our original poster got. (And
if there was that kind of resistance in the path to earth, the socket's
earth connection's not exactly in order!).
From the details given, there's a (possibly intermittent) fault which needs
sorting out. It's not clear from what we've heard whether the socket was
the source of the 'tingle', with mains current passing through the OP's
body on its way to earth, or its 'sink' - for example, if there's a
floorboard nail which is just about contact with a live (only), and the OP
stands on it, the surrounding floorboards won't give a decent path to
earth so our man won't feel anything; but touching a well-earthed point
- the socket cover if all the wiring's in order - creates a path to earth
which our man can feel. (In such a case the strength of the 'tingle' is
much dependant on how effective a contact he has with the source: do a
trick like this in bare feet and you might not wake up at all :-(
Other uglies can happen with TV/video/sat etc. kit: some of these have
two-pin mains connectors, and then internal circuitry which makes the
aerial outer float to halfway between the live and neutral voltages. The
resistance is high enough not to make the amount of current which flows
dangerous to life, but you still feel a real and unpleasant tingle if
you become the earth path for this voltage.
I'd definitely want to know what caused the 'tingle': what's an unpleasant
weirdness on one occasion can become something much more dangerous next
My DVD player does this. If you touch the metal casing you get a very
faint tingle. The metal mag-mount aerial I used to have on a mobile
phone used to do it too if the phone was plugged into the charger, even
if the phone itself was off.
I assume that the casing/0v DC side of these things isn't really 0v. A
normal 4-diode rectifier won't give a flat 0v DC but more of a ----
which means if the 0v isn't really 0v relative to your own body's
potential you'll feel the pulsing.
Interestingly, since I put a TV card in the computer (in another room)
and connected the aerial lead into that (earthed chassis) the DVD player
which is hooked up to the TV which is hooked up to the same aerial
arrangement no longer gives me that tingle. If I remove the aerial lead
from the PC the effect comes back!
Yes - you're then passing a small leakage current from your DVD player to
the house earth through the aerial lead and the chassis of your PeeCee.
(And if the DVD is on an RCD socket, that leakage is bringing the RCD a
little closer to its tripping threshold; though the current is likely
to be under a milliamp, so on its own it's a long way from causing an
I'd be surprised if the circuitry responsible for the leakage was as far
'inside' as a bridge rectifier on the low-voltage side, though: more
likely suppression components on the live side of a switch-mode PSU.
But I'm a software type by profession, not an EE, so this is hobbyist-level
guesswork rather than certified circuit designer's opinion ;-)
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