In the process of having our house rewired (1970's wiring done by spider
man!) and the discussion of bonding came up.
As we have none at all, it has already been put in, but the query I have
is, should one be unfortunate enough to touch a bonded item (sink/tap
etc) and a live source, surely the resulting electrocution would be far
more severe than an un-bonded house?

I know theoretically you shouldn't be able to reach any electrical
source while touching bonded "bits" but that's never going to happen, so
is bonding MORE of a health risk than getting a little tingle from an
un-bonded house?

After all, you're more likely to get a shock from exposed electrical
appliances than you are from a wire somehow connecting with the copper
pipes etc?

Just a point for discussion rather than a "thats the law" kind of reply.
Ta.

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"Pet" wrote in message
...

[...] should one be unfortunate enough to touch a bonded item
(sink/tap etc) and a live source, surely the resulting electrocution
would be far more severe than an un-bonded house?

The shock might or might not be more severe (depending on, for example,
whether your water service pipe is plastic or metal). Talking about the
severity of electrocution though is a little pointless: dead is dead.

I know theoretically you shouldn't be able to reach any electrical
source while touching bonded "bits" but that's never going to happen,

That's irrelevant. Earthing and equipotential bonding are measures to
prevent electric shock from 'indirect contact' - i.e. contact with accesible
parts which have become live as the result of a fault. Protection against
shock from 'direct contact' relies on other measures - principally
insulation! The wiring regulations (BS 7671) recognise the use of residual
current devices (RCD, RCCB, RCBO) as a _supplementary_ measure against
direct contact. That's why RCD protection is required for socket-outlets
likely to be used to supply portable equipment outdoors.

so is bonding MORE of a health risk than getting a little tingle
from an un-bonded house?

Protection against shock from indirect contact by 'non-conducting location'
is recognised in BS 7671, but not for domestic situations where it would be
completely impractical to implement.

After all, you're more likely to get a shock from exposed electrical
appliances than you are from a wire somehow connecting with the
copper pipes etc?

The EEBADS measure (earthed equipotential bonding and automatic
disconnection of supply) is there to ensure that the 'touch voltage' between
accessible metal items, be they electrical or not, is constrained to a safe
combination of voltage and time. Bonding ensures that the same earth
reference point is used for both the earthed electrical items
('exposed-conductive-parts') and non-electrical metalwork
('extraneous-conductive-parts'). Without bonding, the touch voltage could
be higher, especially with PME supplies.

Just a point for discussion rather than a "thats the law" kind
of reply.

It's not the law yet, but a public electricity supplier can refuse to
connect you if your wiring does not comply with the 'British standard
requirements - i.e. BS 7671. So thou shall't bond.

For further (fairly technical) background on why the wiring regulations are
as they are I recommend Paul Cook's Commentary - see
http://www.amazon.co.uk/exec/obidos/ASIN/0852962371/ (and note the updates
published at http://www.iee.org/Publish/WireRegs/updates.cfm).

HTH
--
Andy

"Andy Wade" wrote in message
...

It's not the law yet, but a public electricity supplier can refuse to
connect you if your wiring does not comply with the 'British standard
requirements - i.e. BS 7671. So thou shall't bond.

Christian was recommending not to bond bathrooms the other day. Am I
confusing two issues here ?

Thanks.

In article ,
"Andy Wade" writes:

It's not the law yet, but a public electricity supplier can refuse to
connect you if your wiring does not comply with the 'British standard
requirements - i.e. BS 7671. So thou shall't bond.

It's in The Electricity Safety, Quality and Continuity Regulations 2002,
which came into force on 31st January 2003.

--
Andrew Gabriel

Andy Wade wrote:

snip
For further (fairly technical) background on why the wiring regulations are
as they are I recommend Paul Cook's Commentary - see
http://www.amazon.co.uk/exec/obidos/ASIN/0852962371/ (and note the updates
published at http://www.iee.org/Publish/WireRegs/updates.cfm).

HTH

Thanks for your time Andy.
My concern arose after getting a 120v shock from our microwave oven
whilst leaning against the stainless drainer to remove some blinds.

The socket the Microwave was plugged into had a fractured Neutral (not
connected) so, the 120v from the microwave case screw could have been
far greater than a "tingle" if the sink had been bonded?

And, If it were bonded, would such a neutral fault/shock have tripped
the RCD? as on this occasion it didn't.


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In message ,
Pet wrote:


My concern arose after getting a 120v shock from our microwave oven
whilst leaning against the stainless drainer to remove some blinds.

The socket the Microwave was plugged into had a fractured Neutral (not
connected)

That's an interesting diagnosis. The case shouldn't be live under any
circumstances (well, not these days anyway), and unless you have a high
impedance supply and the neutral in the socket connected itself to Earth
I'm not sure how this happened... and why 120V?

so, the 120v from the microwave case screw could have been
far greater than a "tingle" if the sink had been bonded?


Possibly in this case because:

And, If it were bonded, would such a neutral fault/shock have tripped
the RCD? as on this occasion it didn't.



It seems to me as if as well as a neutral fault you also have suspect
earthing.

On a TN- supply if any part of an earthed object becomes live (as you
are implying the case of your microwave did) then enough current should
normally flow to blow the circuit fuse or trip the breaker. This is why
a whole-installation RCD is unneccessary for these supplies.

With a TT supply (local earth rod) the impedance of the earth path is
usually too high for this to happen, and so whole-installation RCDs are
required. We won't get into the types here, but the fact is that they
trip with minute amounts of current and your RCD *should* have
disconnected the supply the moment the case of your microwave became
live; it should not have had to wait for you to touch it.

You don't have a double-insulated microwave, do you? If so, it is highly
suspect and needs checking out.

The problem that bonding is designed to address is that although you
would think that your (say) cold water pipe shouldn't have anything to
do with your electrics, it is in fact probably quite well attached to
the electrical system through the earth. The bonding regulations are
there in order to ensure that any metal parts which could be "earthy"
are connected together. In that instance, if the case of your microwave
became live, then rather than the pipework being at (near) earth
potential, it would rise (due to the bonding) to the same potential as
the case. This protects you during the finite period it takes for a fuse
/ MCB to blow, and further protects you should circumstances conspire to
prevent them blowing.

Should you then happen to touch both live case and bonded metalwork,
rather than some current flowing, no current should be able to flow
because both are at the same potential. Sounds silly, but it works.

Supplementary bonding is only strictly required in a bathroom because it
is here where your body's resistance is lowest. Whether or not to
install it in a kitchen is a moot point; the OSG (guidance from the IEE)
suggests it isn't usually necessary, but the electrician's "bible" (John
Whitfield's book) insists that it is.

Where supplementary bonding *isn't* required is when the metalwork in
question is effectively isolated from the earth. This could be, for
example, a metal door frame or a metal radiator supplied by plastic
pipes: beyond a certain length of pipe (somewhere around 1m) the
resistance of the water is high enough to be able to consider that the
radiator isn't "earthy" at all.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... The ultimate mail reader is here!!!!

Pet wrote:
Andy Wade wrote:

snip
For further (fairly technical) background on why the wiring regulations are
as they are I recommend Paul Cook's Commentary - see
http://www.amazon.co.uk/exec/obidos/ASIN/0852962371/ (and note the updates
published at http://www.iee.org/Publish/WireRegs/updates.cfm).

HTH

Thanks for your time Andy.
My concern arose after getting a 120v shock from our microwave oven
whilst leaning against the stainless drainer to remove some blinds.

The socket the Microwave was plugged into had a fractured Neutral (not
connected) so, the 120v from the microwave case screw could have been
far greater than a "tingle" if the sink had been bonded?

And, If it were bonded, would such a neutral fault/shock have tripped
the RCD? as on this occasion it didn't.

My feeling is that supplementary bonding wouldn't have made any
difference in the above case.

The sink will almost certainly be pretty solidly connected to your
wiring earth because of the requirement to bond to incoming water main.
Even if that bonding wasn't in place there's a fairly good chance that
the sink will be connected to earth by the pipework anyway. The only
way that the sink could be (relatively) isolated is if it had all
plastic plumbing, in that case you'd be better off it it *wasn't*
bonded in the above scenario.

The real cause of you getting a shock would appear to be that the
earthing on the microwave had failed. If its case had been correctly
connected to the wiring earth you wouldn't have got a shock regardless
of the state of the neutral connection. I don't really understand how
your 'fractured neutral' caused the microwave to be live.

--
Chris Green

Christian was recommending not to bond bathrooms the other day. Am I
confusing two issues here ?

Only under specific circumstances.

The basic premise of the OP is correct. It is safer to have isolated
metalwork in the bathroom than to have earth bonded. However, if there is a
chance of earth bonding by whatever means, then it is much safer to ensure
that all the metalwork agrees what that earth is by doing the supplementary
bonding.

The result of this is that if the parts are already isolated by being
connected via plastic pipework and not having an electrical connection and
not touching structural metalwork in the building, then supplementary
bonding should be omitted for that item (usually a bath or radiator) to
maintain that isolation. If, however, there is a chance that the metalwork
might be earthed in any way (via pipes or whatever), then the supplementary
bonding should be applied.

Best: Complete isolation.
OK: Supplementary bonding
Unacceptable: Extraneously earthed, but not supplementary bonded

Christian.

wrote:

The real cause of you getting a shock would appear to be that the
earthing on the microwave had failed. If its case had been correctly
connected to the wiring earth you wouldn't have got a shock regardless
of the state of the neutral connection. I don't really understand how
your 'fractured neutral' caused the microwave to be live.

No, nor me, unless it was touching the earth.... ?
As for the 120v (measured potential between sink and Microwave case, I
just assumed it was a half wave (?) of the 240v

Either way, both have been replaced and the bonding hs been run to the
taps/sink.

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Are there any statistics anywhere to support the case for supplementary bonding?

i.e. How many deaths can be directly attributed to the lack of supplementary
bonding? Any period, any country.

In article ,
Steve Firth wrote:
I went down in the mornign to make tea, as I touched the cold tap I had
an "interesting" experience. Probably made worse by concrete floor and
no shoes.

I didn't die though.

Proof?

--
*Ah, I see the f**k-up fairy has visited us again

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

I didn't die though.


Proof?

That if the bonding wire hadn't been installed there would have been no
electricity running to the sink! and a far safer situation.


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That if the bonding wire hadn't been installed there would have been no
electricity running to the sink! and a far safer situation.

Yes, supplementary bonding is for bathrooms. The kitchen sink shouldn't have
been bonded, although if fed through main bonded metal pipework, the effect
of supplementary bonding would have been minimal.

Christian.