I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding'
into a brief article on the wiki:
	http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding

Would folks like to cast an eye over it and suggest (or better still,
write :-)) any improvements.

-- 
John Stumbles

Who's *really* behind all these conspiracy theories?

John Stumbles wrote:
> I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding'
> into a brief article on the wiki:
> 	http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
> 
> Would folks like to cast an eye over it and suggest (or better still,
> write :-)) any improvements.

Shall we add:

Conductor sizes and clamps required
a list of things that do not require bonding but are often incorrectly 
assumed to be in need of it? (Kitchen sinks etc)

-- 
Cheers,

John.

/=================================================================\
|          Internode Ltd -  http://www.internode.co.uk            |
|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

In an earlier contribution to this discussion,
John Rumm   wrote:

> John Stumbles wrote:
>> I've just Persaud-ed John Rumm's piece from the thread 'Earth
>> Bonding' into a brief article on the wiki:
>> http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
>>
>> Would folks like to cast an eye over it and suggest (or better still,
>> write :-)) any improvements.
>
> Shall we add:
>
> Conductor sizes and clamps required
> a list of things that do not require bonding but are often incorrectly
> assumed to be in need of it? (Kitchen sinks etc)
>

If appropriate, I would like to see each of the different incoming mains 
earthing schemes described, together with the implications of each for 
consumer wiring and earthing/bonding. This is something which I've never 
totally got my head round, and having it described in the Wiki would be 
great.
-- 
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

In article ,
	"Roger Mills"  writes:
> 
> If appropriate, I would like to see each of the different incoming mains 
> earthing schemes described, together with the implications of each for 
> consumer wiring and earthing/bonding. This is something which I've never 
> totally got my head round, and having it described in the Wiki would be 
> great.

It's currently in the FAQ.
http://www.diyfaq.org.uk/electrical/electrical.html#system

-- 
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:
> In article ,
> 	"Roger Mills"  writes:
>> If appropriate, I would like to see each of the different incoming mains 
>> earthing schemes described, together with the implications of each for 
>> consumer wiring and earthing/bonding. This is something which I've never 
>> totally got my head round, and having it described in the Wiki would be 
>> great.
> 
> It's currently in the FAQ.
> http://www.diyfaq.org.uk/electrical/electrical.html#system

There is more in the wiki as well:

http://wiki.diyfaq.org.uk/index.php?title=Earthing_Types
http://wiki.diyfaq.org.uk/index.php?title=TT_Earthing
http://wiki.diyfaq.org.uk/index.php?title=Ufer_Earthing

That earthing and bonding article could be a good place the hang links 
to the rest of the the other bits as well.

Not sure if the implications of different earthing schemes are perhaps 
better dealt with in the articles describing things that are affected - 
e.g. the taking electricity outside article talking about implications 
of  exported earths with PME earthing. I can see pros and cons. Perhaps 
a little duplication would not be a bad thing in this case.


-- 
Cheers,

John.

/=================================================================\
|          Internode Ltd -  http://www.internode.co.uk            |
|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

On Jul 5, 5:13 pm, John Stumbles  wrote:

> I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding'
> into a brief article on the wiki:
>        http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
>
> Would folks like to cast an eye over it and suggest (or better still,
> write :-)) any improvements.


A nice helpful article.


A few details to chew on - I'm putting them here as some I'm sure are
best discussed first.


> It will also limit the voltage rise of anything earthed that one can touch to a safe level (under 50V typically) during the fault.

TT earthing is unable to limit V rise to 50v, and TT is no rarity.
Also some older non-TTs fail to limit to 50v.

suggestion: (under 50v for some installation types) or (under 50v in
many cases)


> taps would expose one to a 230V potential difference, causing electrocution.

suggest: taps would expose one to a 230V potential difference, causing
a risk of electrocution.

There are a few reasons why its a risk rather than a cert.


> However if the taps are bonded together then both taps might be at mains voltage (230V) under fault conditions, but touching both exposes one to zero volts of potential difference.

Its often said, and theres a valid point in there of course, but i'm
not convinced its actually true. A wet person standing on a concrete
ground floor is surely liable to experience a painful pd between taps
and floor.


> Equipotential zones only work where all "extraneous-conductive" parts (such as the earth wires of any circuits feeding power into the room as well as metal plumbing) are securely connected together and there are no conductive items or surfaces connected to earth.

Conductive items or surfaces connected to earth are not a problem in
such a scheme, as long as they're bonded. And this is normal. The fact
that equi bonding is in practice normally earthed is perhaps one of
the reasons for popular confusion.

If we take it a step further, equi bonding also (often but certainly
not always) is effective where an earthed bathroom item is _not_ part
of the equi bonding, for the reason that under fault conditions the
rise of pd between the equi bonded and the earthed items isnt high
enough to cause a nasty. Even with a TT install this is usually the
case, since almost any fault causing a rise in V on the equi would
also cause the same V rise on the earthed item - not in 100% of cases
but normally yes.


It may also be worth mentioning the various arguments against equi
bonding - and bear in mind the 17th is significantly relaxing the
requirement for equi, so its pretty relevant if one wants to
understand it properly.



> In reality you will often have a connection by default via the circuit protective conductors of any circuits that are included in the equipotential bonding.

... or more often via copper pipes


NT

meow2222@care2.com wrote:
> On Jul 5, 5:13 pm, John Stumbles  wrote:
> 
>> I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding'
>> into a brief article on the wiki:
>>        http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
>>
>> Would folks like to cast an eye over it and suggest (or better still,
>> write :-)) any improvements.
> 
> 
> A nice helpful article.
> 
> 
> A few details to chew on - I'm putting them here as some I'm sure are
> best discussed first.
> 
> 
>> It will also limit the voltage rise of anything earthed that one can touch to a safe level (under 50V typically) during the fault.
> 
> TT earthing is unable to limit V rise to 50v, and TT is no rarity.
> Also some older non-TTs fail to limit to 50v.
> 
> suggestion: (under 50v for some installation types) or (under 50v in
> many cases)

Hence why additional protection (RCD) is required...

>> taps would expose one to a 230V potential difference, causing electrocution.
> 
> suggest: taps would expose one to a 230V potential difference, causing
> a risk of electrocution.

I would expect a solid connection between mains and earth across the 
hands would be fatal in the vast majority of cases.

> 
> There are a few reasons why its a risk rather than a cert.
> 
> 
>> However if the taps are bonded together then both taps might be at mains voltage (230V) under fault conditions, but touching both exposes one to zero volts of potential difference.
> 
> Its often said, and theres a valid point in there of course, but i'm
> not convinced its actually true. A wet person standing on a concrete
> ground floor is surely liable to experience a painful pd between taps
> and floor.

Not often you have a bare concrete floor. Normally there will be tiles, 
or carpet, or vinyl, or cork etc.

>> Equipotential zones only work where all "extraneous-conductive" parts (such as the earth wires of any circuits feeding power into the room as well as metal plumbing) are securely connected together and there are no conductive items or surfaces connected to earth.
> 
> Conductive items or surfaces connected to earth are not a problem in
> such a scheme, as long as they're bonded. And this is normal. The fact
> that equi bonding is in practice normally earthed is perhaps one of
> the reasons for popular confusion.

Yup, true. Although its not a requirement that is is. It works just fine 
without.


> If we take it a step further, equi bonding also (often but certainly
> not always) is effective where an earthed bathroom item is _not_ part
> of the equi bonding, for the reason that under fault conditions the
> rise of pd between the equi bonded and the earthed items isnt high
> enough to cause a nasty. Even with a TT install this is usually the
> case, since almost any fault causing a rise in V on the equi would
> also cause the same V rise on the earthed item - not in 100% of cases
> but normally yes.
> 
> 
> It may also be worth mentioning the various arguments against equi
> bonding - and bear in mind the 17th is significantly relaxing the
> requirement for equi, so its pretty relevant if one wants to
> understand it properly.

I think the 17th recognises the complexity if the concept and funds ways 
to make it a non issue.

>> In reality you will often have a connection by default via the circuit protective conductors of any circuits that are included in the equipotential bonding.
> 
> ... or more often via copper pipes

well both if done right...


-- 
Cheers,

John.

/=================================================================\
|          Internode Ltd -  http://www.internode.co.uk            |
|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

John Stumbles wrote:
> I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding'
> into a brief article on the wiki:
> http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding


I now understand the concept as explained by John, but one thing I'm not 
clear on.

For example, in a wash basin.  The hot tap is supplied via copper pipe & 
fittings.  The cold is supplied via copper pipe & a plastic tap connector. 
The bonding isn't now continuous?

If the plastic tap connector were replaced by one of the metal braided 
flexible tap connectors 
http://www.screwfix.com/prods/18417/Plumbing/Flexible-Hoses/Flex-Tap-Connector-Cold-Water-Valve-15mm-x

Will that conduct electricity & complete the bonding.?  Sorry, probably not 
using the correct terms.


-- 
Dave - The Medway Handyman
www.medwayhandyman.co.uk

The Medway Handyman wrote:
> John Stumbles wrote:
>> I've just Persaud-ed John Rumm's piece from the thread 'Earth
>> Bonding' into a brief article on the wiki:
>> http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
>
>
> I now understand the concept as explained by John, but one thing I'm
> not clear on.
>
> For example, in a wash basin.  The hot tap is supplied via copper
> pipe & fittings.  The cold is supplied via copper pipe & a plastic
> tap connector. The bonding isn't now continuous?
>
> If the plastic tap connector were replaced by one of the metal braided
> flexible tap connectors
> http://www.screwfix.com/prods/18417/Plumbing/Flexible-Hoses/Flex-Tap-Connector-Cold-Water-Valve-15mm-x
>
> Will that conduct electricity & complete the bonding.?  Sorry,
> probably not using the correct terms.

Forgot to add - would things be OK as long as both taps were bonded in the 
same way?



-- 
Dave - The Medway Handyman
www.medwayhandyman.co.uk

"The Medway Handyman"  wrote in message 
news:kN%bk.21541$E41.19929@text.news.virginmedia.com...
>
>
> The Medway Handyman wrote:
>> John Stumbles wrote:
>>> I've just Persaud-ed John Rumm's piece from the thread 'Earth
>>> Bonding' into a brief article on the wiki:
>>> http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
>>
>>
>> I now understand the concept as explained by John, but one thing I'm
>> not clear on.
>>
>> For example, in a wash basin.  The hot tap is supplied via copper
>> pipe & fittings.  The cold is supplied via copper pipe & a plastic
>> tap connector. The bonding isn't now continuous?
>>
>> If the plastic tap connector were replaced by one of the metal braided
>> flexible tap connectors
>> http://www.screwfix.com/prods/18417/Plumbing/Flexible-Hoses/Flex-Tap-Connector-Cold-Water-Valve-15mm-x
>>
>> Will that conduct electricity & complete the bonding.?  Sorry,
>> probably not using the correct terms.
>
> Forgot to add - would things be OK as long as both taps were bonded in the 
> same way?
>
>

Assuming that the copper pipes supplying the hot and cold are bonded 
together (this is usually done behind the pedastal) then it does not matter 
if the pipes are supplied by plastic connectors or not. The supply to the 
taps is now potentially balanced and there is no way either if the taps will 
be at a different voltage each other. If one tap is supplied by a plastic 
connector and is insulated from the pipe then it would not be an exposed 
conductive part and so would not need bonding. If the the tap is not 
insulated from the pipework (copperpipework all the way)  then the bonding 
is already complete.

Adam

On Sun, 06 Jul 2008 01:01:30 +0100, John Rumm wrote:

--8<-- snippetty-snip --8<--

OK, taking on board what you folks (JR & NT) in particular and others have
said I've rewritten the first few sections:

"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Earthing and bonding are often confused (sometimes even referred to as
"earth bonding"). This article attempts to clarify the subject.

Earthing
========

Earthing ensures that in the event of a fault a large fault current will
flow causing rapid operation of a Circuit Protective Device (fuse or
circuit breaker) promptly disconnecting the supply. For example suppose
that a live wire in a washing machine has been positioned incorrectly so
that it rubs on a sharp metal edge of the casing when the machine is
running, and the insulation has now worn away enough that the wire makes
contact with the metal of the case. Since the case is connected (via its
13A plug) to mains earth a high current will flow which will blow the fuse
in the plug.

Earthing is also designed to limit the voltage rise of anything earthed
that one can touch to a safe level (specified as being under 50V AC)
during the fault. Thus if someone is touching the washing machine case
when the fault occurs the voltage they are exposed to, and the time for
which they are exposed, are small enough that they should not be at
significant risk of shock injury.

The size of earthing conductors and characteristics of fuses and other
protective devices are designed to ensure that a fault is cleared within 5
seconds for all faults, and within 0.4 seconds for circuits feeding socket
outlets (to which our washing machines etc, which may be touched, are
connected).

Bonding
=======
Two types of bonding are recognised: Main and Supplementary

Main Bonding
------------

Main bonding is the electrical connection together of incoming service
pipes (usually water and gas or oil) to the main electrical earth (at the
incoming electricity cable and meter). This ensures that (metallic) gas
and water installation pipework running through a building are at the
electrical earth potential.

Supplementary bonding
---------------------

Supplementary, equipotential or cross bonding is usually found in special
locations containing a bath or shower. Unlike earthing it is not designed
to clear a fault or limit the absolute touch voltage. What it does is
electrically tie together all extraneous-conductive parts (pipe or other
services etc) that could under fault conditions introduce a dangerous
potential into the room. For example suppose an immersion heater or inline
instantaneous electric heater develops a fault which makes the hot water
pipework electrically live. (Of course this also supposes that the
pipework is not earthed and the appliance is not properly earthed: which
should never happen but the regulations adopt a belt and braces approach.)
Without bonding such a fault would result in the hot taps being at 230V
while the cold taps might offer a path to earth via the rising main: this
would be a very dangerous situation since touching both hot and cold taps
would expose one to a 230V potential difference across the arms and chest
(including heart) probably causing severe injury or death.

However if the pipework feeding both hot and cold taps is bonded together
then both taps might be at mains voltage (230V) under fault conditions,
but touching both exposes one to a potential difference of zero volts.
(Actually the bonding may fail to tie all elements together at exactly the
same potential, but it is designed to limit any potential difference to
50V or less.)

For equipotential zones to work all extraneous-conductive parts (such as
the earth wires of any circuits feeding power into the room as well as
metal plumbing - central heating as well as hot and cold water) must be
securely electrically connected together, and there must be no conductive
items or surfaces connected to earth.

Note that it is the conductive pipework (etc) entering the special
location (bathroom etc) which must be bonded: if there is a mixture of
metal and plastic pipework, plastic plumbing connectors etc, then it is
the pipework coming into the room, not any downstream of plastic sections,
which must be bonded.

Note also that there is no requirement to explicitly connect supplementary
bonding to the main earth terminal in or adjacent to the consumer unit,
though in practice there will often be a connection by default via the
circuit protective conductors of any circuits that are included in the
equipotential bonding.


-- 
YAPH http://yaph.co.uk

Pessimists are never disappointed

On Jul 5, 5:13 pm, John Stumbles  wrote:

> I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding'
> into a brief article on the wiki:
>        http://wiki.diyfaq.org.uk/index.php?title=Earthing_and_Bonding
>
> Would folks like to cast an eye over it and suggest (or better still,
> write :-)) any improvements.


On a slightly less serious note, I bet the wiki would get more hits if
you changed the title to earthing & bondage


NT

YAPH wrote:

> OK, taking on board what you folks (JR & NT) in particular and others have
> said I've rewritten the first few sections:

Yup, that seems to read quite well...

> Supplementary bonding
> ---------------------
> 
> Supplementary, equipotential or cross bonding is usually found in special
> locations containing a bath or shower. Unlike earthing it is not designed
> to clear a fault or limit the absolute touch voltage. What it does is
> electrically tie together all extraneous-conductive parts (pipe or other
> services etc) that could under fault conditions introduce a dangerous
> potential into the room. For example suppose an immersion heater or inline
> instantaneous electric heater develops a fault which makes the hot water
> pipework electrically live. (Of course this also supposes that the
> pipework is not earthed and the appliance is not properly earthed: which
> should never happen but the regulations adopt a belt and braces approach.)
> Without bonding such a fault would result in the hot taps being at 230V
> while the cold taps might offer a path to earth via the rising main: this
> would be a very dangerous situation since touching both hot and cold taps
> would expose one to a 230V potential difference across the arms and chest
> (including heart) probably causing severe injury or death.

I wonder if it is worth including a note somewhere about the extra 
significance of bonding in PME installations (with regard to 
disconnection of a suppliers PEN conductor in particular - which is 
probably a more likely real world danger for users with overhead 
supplies and PME)



-- 
Cheers,

John.

/=================================================================\
|          Internode Ltd -  http://www.internode.co.uk            |
|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

"YAPH"  wrote in message 
news:pC4ck.168010$8k.51895@newsfe18.ams2...
> On Sun, 06 Jul 2008 01:01:30 +0100, John Rumm wrote:
>
> --8<-- snippetty-snip --8<--
>
> OK, taking on board what you folks (JR & NT) in particular and others have
> said I've rewritten the first few sections:
>
> """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
>

> Bonding
> =======
> Two types of bonding are recognised: Main and Supplementary
>



> Main Bonding
> ------------
>
> Main bonding is the electrical connection together of incoming service
> pipes (usually water and gas or oil) to the main electrical earth (at the
> incoming electricity cable and meter). This ensures that (metallic) gas
> and water installation pipework running through a building are at the
> electrical earth potential.


I have to disagree. Main bonding is there to ensure that the incoming 
services (or any extraneous conducive part such as structual metalwork) is 
at the same potential as the suppliers earth or on a TT system the owners 
earth.

A metal incoming water supply will be at earth potential. There is no need 
to bond it to the CU to make it an electrical earth potential. The reason 
for main bonding is in case of a problem with the incoming supply.
For example if the earth from the supplier was to become live then all the 
metalwork in the sockets, switches, washing machines could become live.
Main bonding will bring all the earthed points (the extraneous condutive 
parts) up to mains potential as well so that you cannot touch an earthed 
stoptap etc and a now live metal lightswitch.


> Supplementary, equipotential or cross bonding is usually found in special
> locations containing a bath or shower. Unlike earthing it is not designed
> to clear a fault or limit the absolute touch voltage. What it does is
> electrically tie together all extraneous-conductive parts (pipe or other
> services etc) that could under fault conditions introduce a dangerous
> potential into the room. For example suppose an immersion heater or inline
> instantaneous electric heater develops a fault which makes the hot water
> pipework electrically live. (Of course this also supposes that the
> pipework is not earthed and the appliance is not properly earthed: which
> should never happen but the regulations adopt a belt and braces approach.)
> Without bonding such a fault would result in the hot taps being at 230V
> while the cold taps might offer a path to earth via the rising main: this
> would be a very dangerous situation since touching both hot and cold taps
> would expose one to a 230V potential difference across the arms and chest
> (including heart) probably causing severe injury or death.
>
> However if the pipework feeding both hot and cold taps is bonded together
> then both taps might be at mains voltage (230V) under fault conditions,
> but touching both exposes one to a potential difference of zero volts.
> (Actually the bonding may fail to tie all elements together at exactly the
> same potential, but it is designed to limit any potential difference to
> 50V or less.)
>
> For equipotential zones to work all extraneous-conductive parts (such as
> the earth wires of any circuits feeding power into the room as well as
> metal plumbing - central heating as well as hot and cold water) must be
> securely electrically connected together, and there must be no conductive
> items or surfaces connected to earth.

There way well be an extraneous condutive parts in these special locations. 
These would have to be protected under the main bonding though. Stop taps in 
bathrooms are not uncommon.

> Note that it is the conductive pipework (etc) entering the special
> location (bathroom etc) which must be bonded: if there is a mixture of
> metal and plastic pipework, plastic plumbing connectors etc, then it is
> the pipework coming into the room, not any downstream of plastic sections,
> which must be bonded.
>
> Note also that there is no requirement to explicitly connect supplementary
> bonding to the main earth terminal in or adjacent to the consumer unit,
> though in practice there will often be a connection by default via the
> circuit protective conductors of any circuits that are included in the
> equipotential bonding.

Just my opinion. Not a dig at your work.

Adam

"ARWadworth"  wrote in message 
news:Cf5ck.21780$E41.3730@text.news.virginmedia.com...
>

>
> Just my opinion. Not a dig at your work.

Should say "Not a dig at your work on the article you wrote" :-)

Adam

On Sun, 06 Jul 2008 16:01:04 +0100, John Rumm wrote:

> I wonder if it is worth including a note somewhere about the extra 
> significance of bonding in PME installations (with regard to 
> disconnection of a suppliers PEN conductor in particular - which is 
> probably a more likely real world danger for users with overhead 
> supplies and PME)

Maybe, but perhaps it should go in the Types of Earthing article (I also
excised some lines of NT's to the discussion page with a suggestion they
should go in that article too.)



-- 
YAPH http://yaph.co.uk

I used to think the brain was the most interesting part of the body
                        - until I realised what was telling me that

On Sun, 06 Jul 2008 15:10:26 +0000, ARWadworth wrote:


>> Main Bonding
>> ------------
>>
>> Main bonding is the electrical connection together of incoming service
>> pipes (usually water and gas or oil) to the main electrical earth (at the
>> incoming electricity cable and meter). This ensures that (metallic) gas
>> and water installation pipework running through a building are at the
>> electrical earth potential.
> 
> 
> I have to disagree. Main bonding is there to ensure that the incoming 
> services (or any extraneous conducive part such as structual metalwork) is 
> at the same potential as the suppliers earth or on a TT system the owners 
> earth.

Well you could read "at the electrical earth potential" as meaning that,
but it could do with clarifying if that's what it does mean. TBH I dodged
that issue as I'm not sure that is the reason: I just know one's got to do
it! 

> .... The reason 
> for main bonding is in case of a problem with the incoming supply.
> For example if the earth from the supplier was to become live then all the 
> metalwork in the sockets, switches, washing machines could become live.
> Main bonding will bring all the earthed points (the extraneous condutive 
> parts) up to mains potential as well so that you cannot touch an earthed 
> stoptap etc and a now live metal lightswitch.

What you say makes sense and I'm inclined to agree with your analysis, but
I'd like to see chapter and verse from the regs or suchlike, not just your
or my interpretation/opinion, so I know what's going in the article is
gospel[1]

>> For equipotential zones to work all extraneous-conductive parts (such
>> as the earth wires of any circuits feeding power into the room as well
>> as metal plumbing - central heating as well as hot and cold water) must
>> be securely electrically connected together, and there must be no
>> conductive items or surfaces connected to earth.
> 
> There way well be an extraneous condutive parts in these special
> locations. These would have to be protected under the main bonding
> though. Stop taps in bathrooms are not uncommon.

True, but in that case you have main bonding *and* supplementary bonding
in the bathroom, and your eqipotential bonding is also earthed. I don't
see any contradiction.


[1] or true, as the case many be ;-)



-- 
YAPH http://yaph.co.uk

I forgot to take my amnesia medecine again

On Sun, 06 Jul 2008 07:32:44 -0700, meow2222 wrote:

> On a slightly less serious note, I bet the wiki would get more hits if
> you changed the title to earthing & bondage

Purlease, nooooo - don't set the hot pr0n site spammers off again ;-)

-- 
YAPH http://yaph.co.uk

I forgot to take my amnesia medecine again

"YAPH"  wrote in message 
news:fH5ck.6408$7v1.260@newsfe30.ams2...
> On Sun, 06 Jul 2008 15:10:26 +0000, ARWadworth wrote:
>
>
>>> Main Bonding
>>> ------------
>>>
>>> Main bonding is the electrical connection together of incoming service
>>> pipes (usually water and gas or oil) to the main electrical earth (at 
>>> the
>>> incoming electricity cable and meter). This ensures that (metallic) gas
>>> and water installation pipework running through a building are at the
>>> electrical earth potential.
>>
>>
>> I have to disagree. Main bonding is there to ensure that the incoming
>> services (or any extraneous conducive part such as structual metalwork) 
>> is
>> at the same potential as the suppliers earth or on a TT system the owners
>> earth.
>
> Well you could read "at the electrical earth potential" as meaning that,
> but it could do with clarifying if that's what it does mean. TBH I dodged
> that issue as I'm not sure that is the reason: I just know one's got to do
> it!
>
>> .... The reason
>> for main bonding is in case of a problem with the incoming supply.
>> For example if the earth from the supplier was to become live then all 
>> the
>> metalwork in the sockets, switches, washing machines could become live.
>> Main bonding will bring all the earthed points (the extraneous condutive
>> parts) up to mains potential as well so that you cannot touch an earthed
>> stoptap etc and a now live metal lightswitch.
>
> What you say makes sense and I'm inclined to agree with your analysis, but
> I'd like to see chapter and verse from the regs or suchlike, not just your
> or my interpretation/opinion, so I know what's going in the article is
> gospel[1]
>
The regs tell you what needs to be done not why they need to be done.
Your main bonding part is virtually reg 413-02-02 of the 16th edition. It 
tells you what needs/may need main bonding. My query was with your statement 
"This ensures that (metallic) gas and water installation pipework running 
through a building are at the electrical earth potential."
Maybe a more constructive suggestion would be "This ensures that all 
extraneous conductive parts such as (metallic) gas and water services 
entering a house are at the same potential as the suppliers earth"




You supplementary part uses the term extraneous conduvtive part instead of 
exposed-condutive part. I will re read it later with suggestions. It looks 
good though.

Adam

ARWadworth wrote:

> Maybe a more constructive suggestion would be "This ensures that all 
> extraneous conductive parts such as (metallic) gas and water services 
> entering a house are at the same potential as the suppliers earth"

"as the electrical system's earth" may be better (to account for TT systems)


-- 
Cheers,

John.

/=================================================================\
|          Internode Ltd -  http://www.internode.co.uk            |
|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

YAPH wrote:

> Earthing ensures that in the event of a fault a large fault current will
> flow causing rapid operation of a Circuit Protective Device

The fault current doesn't necessarily have to be 'large'.  In principle 
30 mA will do the trick if the device doing the automatic disconnection 
is an RCD.

> [...] (fuse or circuit breaker) promptly disconnecting the supply.

Or RCD in some circumstances.  (OK "circuit breaker" in its most general 
sense includes RCCBs, but saying "fuse, MCB or RCD" might be clearer for 
most readers.)

> Earthing is also designed to limit the voltage rise of anything earthed
> that one can touch to a safe level (specified as being under 50V AC)
> during the fault.

That's wrong.  Touch voltage can be much higher during an earth fault: 
half-mains or more, due to the voltage drop in the CPC.  Shock 
protection is achieved by limiting the fault duration, not the fault 
voltage.  Only in particular cases is it necessary to provide local 
supplementary bonding to limit the voltage too.

> The size of earthing conductors and characteristics of fuses and other
> protective devices are designed to ensure that a fault is cleared within 5
> seconds for all faults, and within 0.4 seconds for circuits feeding socket
> outlets (to which our washing machines etc, which may be touched, are
> connected).

This is out of date information now.  Permissible disconnection times 
have changed significantly in the 17th ed. and the old distinction 
between socket circuits and fixed equipment has gone.  For 230 V AC 
supplies (incl. 230/400 V 3-ph) the following maxima now apply:

  System                     TN     TT
                           -----  -----
  Final circuits <= 32 A   0.4 s  0.2 s
  Final circuits > 32 A      5 s    1 s
  Distribution circuits      5 s    1 s


Remember the mantra: earthing protects by reducing the duration of touch 
voltages.  Bonding protects by reducing their magnitude.

-- 
Andy

In article , Andy Wade <spambucket@ma
xwell.myzen.co.uk> scribeth thus
>YAPH wrote:
>
>> Earthing ensures that in the event of a fault a large fault current will
>> flow causing rapid operation of a Circuit Protective Device
>
>The fault current doesn't necessarily have to be 'large'.  In principle 
>30 mA will do the trick if the device doing the automatic disconnection 
>is an RCD.
>
>> [...] (fuse or circuit breaker) promptly disconnecting the supply.
>
>Or RCD in some circumstances.  (OK "circuit breaker" in its most general 
>sense includes RCCBs, but saying "fuse, MCB or RCD" might be clearer for 
>most readers.)
>
>> Earthing is also designed to limit the voltage rise of anything earthed
>> that one can touch to a safe level (specified as being under 50V AC)
>> during the fault.
>
>That's wrong.  Touch voltage can be much higher during an earth fault: 
>half-mains or more, due to the voltage drop in the CPC.  Shock 
>protection is achieved by limiting the fault duration, not the fault 
>voltage.  Only in particular cases is it necessary to provide local 
>supplementary bonding to limit the voltage too.
>
>> The size of earthing conductors and characteristics of fuses and other
>> protective devices are designed to ensure that a fault is cleared within 5
>> seconds for all faults, and within 0.4 seconds for circuits feeding socket
>> outlets (to which our washing machines etc, which may be touched, are
>> connected).
>
>This is out of date information now.  Permissible disconnection times 
>have changed significantly in the 17th ed. and the old distinction 
>between socket circuits and fixed equipment has gone.  For 230 V AC 
>supplies (incl. 230/400 V 3-ph) the following maxima now apply:
>
> System                     TN     TT
>                          -----  -----
> Final circuits <= 32 A   0.4 s  0.2 s
> Final circuits > 32 A      5 s    1 s
> Distribution circuits      5 s    1 s
>
>
>Remember the mantra: earthing protects by reducing the duration of touch 
>voltages.  Bonding protects by reducing their magnitude.
>

So is there a "safe time" for excessive current through a body?..

Suppose not...
-- 
Tony Sayer

In article ,
	tony sayer  writes:
> 
> So is there a "safe time" for excessive current through a body?..
> 
> Suppose not...

Safe as in guaranteed -- no.

Safe as in unlikely to do any harm -- certainly.

There are lots of graphs showing the current verses time for
various bad effects on the body. Whilst they disagree quite
markedly in magnitude, they all agree that the longer and
the higher the current flow, the more harmful. 

-- 
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]