In article ,
Doctor Drivel wrote:
http://wiki.diyfaq.org.uk/index.php?...tary _bonding


"What it does is electrically tie together all accessible conductive
parts (pipes, taps, electrical appliances etc) that could under fault
conditions introduce a dangerous potential into the room. "

A rank amateur would look at that and not know what potential is.
"Potential" needs a explanation at this point.

A 'rank amateur' should then just follow the guidance and not question his
betters - that's what these FAQs are for. And if wants to understand the
whys and wherefores can do some simple research.

A little knowledge is a dangerous thing - and aptly shown by those who
query the need for equipotential bonding.

--
*If you tell the truth, you don't have to remember anything.*

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

dennis@home wrote:

But not in a normal house, using normal appliances

Yes, in any electrical installation.

as they metal case will always be bonded to earth.

To speak this language properly you just say "earthed" - not "bonded to
earth." But yes, it will (or should, unless it's Class 2). So what?
That earthing and equipotential bonding are distinct and separate
concepts doesn't imply electrical separation.

[Towel rail example]
Its actually two faults, the earth has been disconnected and the live
insulation has failed, not actually very common.

I said that the o/c circuit protective (earth) conductor was a common
fault. If the case becomes live through an insulation failure that is
indeed a second fault. It's not an unknown situation though because the
first fault can go undetected for years.

As I said unless you are going to modify the appliance you are bonding
to earth.

The casing of the appliance is _earthed_ via its circuit protective
conductor (CPC) - typically the 'earth' wire in a twin-and-earth cable.
In a bathroom, ignoring the 17th ed. for a moment, the casing should
also be _bonded_ to the CPCs of circuits feeding any other equipment in
the room, and to any other extraneous-conductive-parts (E-C-P). The
latter term means anything that can import a potential into the room
(usually, but not necessarily, earth and with the ability to sustain the
flow of a dangerous current. So metal plumbing which might be earthed
elsewhere counts as an E-C-P, but floating items don't. The bonding
might or might not be earthed elsewhere.

That would be the main bonding to where exactly?

Main bonding is the connection of incoming metal services such as gas
and water to the main earth terminal, creating an equipotential zone.
It's absolutely fundamental to the safety of PME supplies where it's
possible for the suppliers combined neutral and earth conductor to come
adrift, leaving all your earthing up at 230 V.

So where do you not bond to earth within the FCU?

The supplementary bonding is connected to the earth terminal in the FCU.
This achieves bonding to the case via the CPC in the flex. There are
other situations where a green-and-yellow wire might be acting as both a
CPC and a bonding conductor.

We bonded huge amounts of metal together but we didn't use green and
yellow earth cable to do it as it wasn't earth.

Earth-free bonding is one of the measures recognised in BS 7671 for
special situations under an engineer's supervision. Green-and-yellow
identifies protective conductors, whether earthed or not, and should
have been used if this is something within the scope of BS 7671.

--
Andy

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


"What it does is electrically tie together all accessible conductive
parts (pipes, taps, electrical appliances etc) that could under fault
conditions introduce a dangerous potential into the room. "

A rank amateur would look at that and not know what potential is.
"Potential" needs a explanation at this point.

Anyone who doesn't understand the word "potential" in relation to
electricity shouldn't go anywhere *near* mains house-wiring!

Well maybe the whole article should not be there then, if only pro
electricians can read it.

In article ,
Doctor Drivel wrote:

"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
Doctor Drivel wrote:


"What it does is electrically tie together all accessible conductive
parts (pipes, taps, electrical appliances etc) that could under fault
conditions introduce a dangerous potential into the room. "

A rank amateur would look at that and not know what potential is.
"Potential" needs a explanation at this point.

Anyone who doesn't understand the word "potential" in relation to
electricity shouldn't go anywhere *near* mains house-wiring!

Well maybe the whole article should not be there then, if only pro
electricians can read it.

The meaning of 'potential' was taught in first year physics when I were a
lad. I'd have thought one such as you - who claims to have a science
degree - to understand it too.

--
*To be intoxicated is to feel sophisticated, but not be able to say it.

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

"Andy Wade" wrote in message
...
dennis@home wrote:

But not in a normal house, using normal appliances

Yes, in any electrical installation.

as they metal case will always be bonded to earth.

To speak this language properly you just say "earthed" - not "bonded to
earth." But yes, it will (or should, unless it's Class 2). So what? That
earthing and equipotential bonding are distinct and separate concepts
doesn't imply electrical separation.

I didn't ay they did.
I just object to being told bonding stuff to earth is wrong when in 99.999%
of homes that is exactly what is done.


[Towel rail example]
Its actually two faults, the earth has been disconnected and the live
insulation has failed, not actually very common.

I said that the o/c circuit protective (earth) conductor was a common
fault. If the case becomes live through an insulation failure that is
indeed a second fault. It's not an unknown situation though because the
first fault can go undetected for years.

As I said unless you are going to modify the appliance you are bonding to
earth.

The casing of the appliance is _earthed_ via its circuit protective
conductor (CPC) - typically the 'earth' wire in a twin-and-earth cable. In
a bathroom, ignoring the 17th ed. for a moment, the casing should also be
_bonded_ to the CPCs of circuits feeding any other equipment in the room,
and to any other extraneous-conductive-parts (E-C-P). The latter term
means anything that can import a potential into the room (usually, but not
necessarily, earth and with the ability to sustain the flow of a dangerous
current. So metal plumbing which might be earthed elsewhere counts as an
E-C-P, but floating items don't. The bonding might or might not be
earthed elsewhere.

That would be the main bonding to where exactly?

Main bonding is the connection of incoming metal services such as gas and
water to the main earth terminal, creating an equipotential zone. It's
absolutely fundamental to the safety of PME supplies where it's possible
for the suppliers combined neutral and earth conductor to come adrift,
leaving all your earthing up at 230 V.

So you agree that I was correct in saying you bond it to earth.


So where do you not bond to earth within the FCU?

The supplementary bonding is connected to the earth terminal in the FCU.
This achieves bonding to the case via the CPC in the flex. There are
other situations where a green-and-yellow wire might be acting as both a
CPC and a bonding conductor.

And again.

I really don't see where you differ from what I said.


We bonded huge amounts of metal together but we didn't use green and
yellow earth cable to do it as it wasn't earth.

Earth-free bonding is one of the measures recognised in BS 7671 for
special situations under an engineer's supervision. Green-and-yellow
identifies protective conductors, whether earthed or not, and should have
been used if this is something within the scope of BS 7671.

--
Andy

dennis@home wrote:

To speak this language properly you just say "earthed" - not "bonded
to earth." But yes, it will (or should, unless it's Class 2). So
what? That earthing and equipotential bonding are distinct and
separate concepts doesn't imply electrical separation.

I didn't ay they did.
I just object to being told bonding stuff to earth is wrong when in
99.999% of homes that is exactly what is done.

Use of the word "bonding" (which has specific meaning in BS7671) in this
context only serves to confuse the issue. Class 1 appliances have an
earth connection certainly - this is common practice. However it is only
common practice to use equipotential bonding in areas of high shock risk
rather than generally. Phrases like "bonded to earth" have no meaning
within the wiring regulations - so if you use them, you can't expect
people to know exactly what you are talking about.

So where do you not bond to earth within the FCU?

The supplementary bonding is connected to the earth terminal in the
FCU. This achieves bonding to the case via the CPC in the flex. There
are other situations where a green-and-yellow wire might be acting as
both a CPC and a bonding conductor.

And again.

I really don't see where you differ from what I said.

There is a significant practical difference...

You might argue that if the installation has main equipotential bonding
in place, and the towel rail has a protective earth connection, then by
default, you also have a equipotential bond between them since there is
an electrical path from the CPC of the towel rail to the water pipe (for
example).

However this fortuitous EQ bond has not been designed to act as a
equipotential bond, and in reality will quite probably fail to do what
is required under fault conditions (i.e. reduce touch voltage between
towel rail and pipework) to a safe level. Separate EQ bonding designed
for the purpose is required to do that, and having it present also acts
as a second line of defence should the CPC for the towel rail not be
connected.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
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Doctor Drivel wrote:

http://wiki.diyfaq.org.uk/index.php?...tary _bonding



"What it does is electrically tie together all accessible conductive
parts (pipes, taps, electrical appliances etc) that could under fault
conditions introduce a dangerous potential into the room. "

A rank amateur would look at that and not know what potential is.
"Potential" needs a explanation at this point.

It is a wiki you know, feel free to add extra description if you think
it would help.


--
Cheers,

John.

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