OK, I've read everything there is to know about the subject on t'interweb
and I'm significantly more confused than when I first started.

Blank canvas - new bathroom - no earth at present. The ceiling is 2.9m high
and the lighting is 12v IP44 rated with an external switch. There's nothing
else electric in the bathroom other than the extractor fan, which is double
insulated.

I have a metal bath, metal towel radiator (NOT electric), metal shower and
(obviously) metal taps. All supply and c/h pipework is copper, all boxed in
above floor level, and the mains water supply to the building is plastic.
SO...

1. I gather I need to earth my lovely chrome towel radiator with an awful
green and yellow cable? How on earth (sorry!) do I do this without having
the earth cable dangling up my wall? Would it be sufficient to bond the
(microbore) pipework inside the boxing (approx 1ft below the towel radiator
itself) or does the actual towel radiator need to have an ugly earth clamp
stuck to it?

1b. If my towel radiator MUST be bonded, why doesn't it have a strategic
point onto which to attach an earth cable?

2. I read somewhere that if the earth cable is within conduit 4mm^2 is
sufficient. Since the earth cable will run (loose) within boxing around the
room, does this count as conduit?

3. OK, so I connect everything together with earth clamps and bits of
wire - where does this ultimately need to go back to? I've read it's NOT a
good idea to take this back to the CU.

4. If I bond everything together within the boxing, to hide unsightly earth
cables, will this be sufficient? (the boxing will have removable panels at
strategic points) i.e. exactly how close to the taps, towel radiator,
shower etc. does the earth wire need to run?

Think that's it! TIA,

Andy

Pecanfan wrote:
3. OK, so I connect everything together with earth clamps and bits of
wire - where does this ultimately need to go back to? I've read it's NOT a
good idea to take this back to the CU.

It doesn't need to go anywhere, the object is to ensure that all the
bits of metal you can touch are at the same potential as each other.

--
Chris Green

"Pecanfan" wrote in message
...
OK, I've read everything there is to know about the subject on t'interweb
and I'm significantly more confused than when I first started.

Blank canvas - new bathroom - no earth at present. The ceiling is 2.9m
high
and the lighting is 12v IP44 rated with an external switch. There's
nothing
else electric in the bathroom other than the extractor fan, which is
double
insulated.

I have a metal bath, metal towel radiator (NOT electric), metal shower and
(obviously) metal taps. All supply and c/h pipework is copper, all boxed
in
above floor level, and the mains water supply to the building is plastic.
SO...

1. I gather I need to earth my lovely chrome towel radiator with an awful
green and yellow cable? How on earth (sorry!) do I do this without having
the earth cable dangling up my wall? Would it be sufficient to bond the
(microbore) pipework inside the boxing (approx 1ft below the towel
radiator
itself) or does the actual towel radiator need to have an ugly earth clamp
stuck to it?

My Collins DIY book shows each microbore pipe bonded AND the radiator too!
My bathroom is not new so there's no way I'm bothering with that: I've only
just
bonded the flow and return radiator pipes and the gas pipe by the CU, they
were
only bonded by indirect means before. Rumor has it that compression fittings
make
good metal to metal contact reliably, so I'm thinking that all this multiple
bonding
(i.e. 3 lots per adiator ) is a bit OTT. Dunno what the regs say exactly.

1b. If my towel radiator MUST be bonded, why doesn't it have a strategic
point onto which to attach an earth cable?

To make life difficult for us. It'll most likely be very well bonded via the
microbore anyway.

2. I read somewhere that if the earth cable is within conduit 4mm^2 is
sufficient. Since the earth cable will run (loose) within boxing around
the
room, does this count as conduit?

I heard it was 4mm2 if protected, but as small as 2.5mm2 if run in
conduit???
Something to do with =60% of the cross sectional area of the local
circuitry
( which is none in my bathroom, unless you count the ceiling light ). I
guess that
means that 2.5mm2 is more than sufficient if the only danger comes from
lighting
circuits.

3. OK, so I connect everything together with earth clamps and bits of
wire - where does this ultimately need to go back to? I've read it's NOT
a
good idea to take this back to the CU.

As the other poster said, it is not necessary AFAIK to take it take to the
main earth
terminal, the fact that all extraneous metal parts in he bathroom are all
connected
together is sufficient.

4. If I bond everything together within the boxing, to hide unsightly
earth
cables, will this be sufficient? (the boxing will have removable panels
at
strategic points) i.e. exactly how close to the taps, towel radiator,
shower etc. does the earth wire need to run?

Not sure about how close. If you have trouble fitting the clamps, post
again: I found out
that the ones that I bought needed disassembly then ressembly in a different
way to work.

Andy.

Think that's it! TIA,

Andy

Pecanfan wrote:

OK, I've read everything there is to know about the subject on t'interweb
and I'm significantly more confused than when I first started.

Blank canvas - new bathroom - no earth at present. The ceiling is 2.9m high
and the lighting is 12v IP44 rated with an external switch. There's nothing
else electric in the bathroom other than the extractor fan, which is double
insulated.

I have a metal bath, metal towel radiator (NOT electric), metal shower and
(obviously) metal taps. All supply and c/h pipework is copper, all boxed in
above floor level, and the mains water supply to the building is plastic.

OK, so the things to be included in the supplementary bonding a bath,
towel rail, pipework to bath and basin taps and (don't forget) the
circuit earth wire (CPC) of the circuit feeding the fan if it's within
the zones. This is the lighting circuit, most probably. (If the fan is
more than 0.6m horizontally from the edge of the bath and more than 2.3m
high then it's outside the zones.)

1. I gather I need to earth my lovely chrome towel radiator with an awful
green and yellow cable? How on earth (sorry!) do I do this without having
the earth cable dangling up my wall? Would it be sufficient to bond the
(microbore) pipework inside the boxing (approx 1ft below the towel radiator
itself) or does the actual towel radiator need to have an ugly earth clamp
stuck to it?

You can bond to the pipework "in close proximity" to the towel rail -
although a normal earth clamp ain't gonna work on microbore tube
(AFAIK). If you don't bond to the rail itself then bond to both the
flow and return pipes, as a precaution against any high resistance
joints in the plumbing.

2. I read somewhere that if the earth cable is within conduit 4mm^2 is
sufficient. Since the earth cable will run (loose) within boxing around the
room, does this count as conduit?

4mm^2 applies if there's no mechanical protection. Where there is
protection you can go down to 2.5mm^2 between
extraneous-conductive-parts (pipework, bath, towel rail) and 1mm^2 for
the bond to the CPC of the lighting circuit. This doesn't make much
difference to the visibility though, so most people just stick to 4mm^2
for everything, thus avoiding the debatable question about whether pipe
boxing counts as protection.

3. OK, so I connect everything together with earth clamps and bits of
wire - where does this ultimately need to go back to?

Nowhere, necessarily...

I've read it's NOT a good idea to take this back to the CU.

.... but it will find its way back to the CU earth terminal via the CPC
of the lighting circuit, and any other circuits feeding equipment in the
bathroom. It's wrong to say "it's NOT a good idea to take this back
to the CU" - but it's simply not necessary to do this separately.

4. If I bond everything together within the boxing, to hide unsightly earth
cables, will this be sufficient? (the boxing will have removable panels at
strategic points) i.e. exactly how close to the taps, towel radiator,
shower etc. does the earth wire need to run?

Yes, supplementary bonding can usually be done very discreetly,
especially if it's not being done as an afterthought. All connections
should be accessible, unless crimped or soldered, and labelled "safety
electrical connection - do not remove".

HTH
--
Andy

Andy Wade wrote:
Pecanfan wrote:


1. I gather I need to earth my lovely chrome towel radiator with
an awful green and yellow cable? How on earth (sorry!) do I do
this without having the earth cable dangling up my wall? Would it
be sufficient to bond the (microbore) pipework inside the boxing
(approx 1ft below the towel radiator itself) or does the actual
towel radiator need to have an ugly earth clamp stuck to it?

I've always just bonded the pipework, just below the valve, and have had
this passed as OK in Periodic Inspections.

If it was necessary to bond the radiator itself and not just the pipe,
then surely by extrapolation that would mean it was necessary to attach
clamps directly to all the bath and sink taps as well?!

You can bond to the pipework "in close proximity" to the towel rail
- although a normal earth clamp ain't gonna work on microbore tube

If not, then what should you use instead? I've never seen any special
microbore clamps available?

David

1. I gather I need to earth my lovely chrome towel radiator with
an awful green and yellow cable? How on earth (sorry!) do I do
this without having the earth cable dangling up my wall? Would it
be sufficient to bond the (microbore) pipework inside the boxing
(approx 1ft below the towel radiator itself) or does the actual
towel radiator need to have an ugly earth clamp stuck to it?

I've always just bonded the pipework, just below the valve, and have had
this passed as OK in Periodic Inspections.

If it was necessary to bond the radiator itself and not just the pipe,
then surely by extrapolation that would mean it was necessary to attach
clamps directly to all the bath and sink taps as well?!

You can bond to the pipework "in close proximity" to the towel rail
- although a normal earth clamp ain't gonna work on microbore tube

If not, then what should you use instead? I've never seen any special
microbore clamps available?

Cheers for the replies - that puts my mind at rest a bit anyway. I meant
2.5mm^2 in the boxing - not 4mm^2 - d'oh!

Building inspector's coming out to this one so will let you know if it all
goes horribly awry! :-)

Andy

1. I gather I need to earth my lovely chrome towel radiator with an awful
green and yellow cable? How on earth (sorry!) do I do this without having
the earth cable dangling up my wall?

Personally, with a blank canvas I would redo the plumbing ensuring at least
1m of plastic between the metalwork (i.e. taps/bath/rad) and the supply.
Then not supplementary bond at all. Short lengths of chrome pipe into the
boxing/under the floorboards are fine. Unforunately, the inspectors may be
too ignorant to realise that such a system is safer than a supplementary
bonded metal one.

The IEE guidance suggesting this as a safer course of action now has
something like "This is not the advice of the IEE" right under the IEE logo,
presumably for legal/insurance reasons. However, its contents are well
considered and based on scientific evidence.

Christian.

Andy Wade wrote:
Pecanfan wrote:

OK, I've read everything there is to know about the subject on
t'interweb
and I'm significantly more confused than when I first started.

OK, so the things to be included in the supplementary bonding a
bath,
towel rail, pipework to bath and basin taps and (don't forget) the
circuit earth wire (CPC) of the circuit feeding the fan if it's
within
the zones.

Hmm, logically (or even illogically) speaking, would you want to
connect the earth bonding to the cpc of a local circuit, wouldn't this
potentially increase the risk of a live to earth fault, as you have
intentionally moved the protective earth bonding to the close vicinity
of the/any live terminals ?

Or am I just being silly ?!

3. OK, so I connect everything together with earth clamps and bits
of
wire - where does this ultimately need to go back to?

Nowhere, necessarily...

I've read it's NOT a good idea to take this back to the CU.

... but it will find its way back to the CU earth terminal via the
CPC
of the lighting circuit, and any other circuits feeding equipment in
the
bathroom. It's wrong to say "it's NOT a good idea to take this
back
to the CU" - but it's simply not necessary to do this separately.

But if it is taken separately you are not intentionally connecting into
junction boxes with adjacent lives, it goes back to the star terminal
at the cu which only contains earths.

Feel free to shoot me down here, but I have just the same bonding
question. I have bonded all exposed metalwork together in the bathroom,
including to a cold water pipe. I don't particularly want to link into
any local circuits, I was going to take back to the TN-S earth point at
the CU.

Let the local circuits find their own earths back via the RCD/CU !

Cheers

Paul.

wrote:
Feel free to shoot me down here, but I have just the same bonding
question. I have bonded all exposed metalwork together in the bathroom,
including to a cold water pipe. I don't particularly want to link into
any local circuits, I was going to take back to the TN-S earth point at
the CU.
Let the local circuits find their own earths back via the RCD/CU !

You run the risk then of (say) a CPC springing out of an earth terminal
and (either in the same place or elsewhere, downstream of the fault)
shorting to a live. This faulty-live-earth could then be taken into the
bathroom and make something live, eg the mounting screws of a flex
outlet feeding a double-insulated towel rail. You could then get a full
240V arm-arm shock from the live apparatus in one hand and the cold tap
in the other.

The point of equipotential bonding is to ensure that you cannot get a
potential difference. If you bond the cold tap to the CPC in the towel
rail FCU, you cannot get a shock *between the two*, even if they are
both live -- because there is no potential difference.

Anything conductive that comes into the bathroom ie could introduce a
potential must be bonded to everything else that might be at a different
potential, so there can be no potential difference. Because these things
usually include services like CPC and metallic water pipes earthed
elsewhere, the euipotential bonding will usually be earthy.

Owain

wrote:

Hmm, logically (or even illogically) speaking, would you want to
connect the earth bonding to the cpc of a local circuit, wouldn't this
potentially increase the risk of a live to earth fault, as you have
intentionally moved the protective earth bonding to the close vicinity
of the/any live terminals ?

Or am I just being silly ?!

Methinks you've missed the whole point of supplementary bonding, which
is to prevent the appearance of voltage differences - "touch voltages"
to use the jargon - as Owain has explained.

But if it is taken separately you are not intentionally connecting into
junction boxes with adjacent lives, it goes back to the star terminal
at the cu which only contains earths.

Ditto. The whole rationale here is *bonding* rather than *earthing*
/per se/. If a bathroom appliance develops an internal earth fault
(phase-CPC short) then there will be a significant voltage drop across
the length of the CPC until the protective device clears the fault.
During this time a potentially lethal touch voltage could exist between
the exposed metal parts of the appliance and (say) the water taps & bathtub.

Example: let's say the appliance is an electric shower unit wired in
10mm^2 T&E cable, which has a 4mm^2 CPC. If the supply to the final
circuit had negligible impedance then an earth fault in the appliance
would cause 10/14 of the mains voltage to appear on the shower unit's
case. The unfortunate user is then possibly standing in an earthed
metal bath with the shower outlet and pipework at ~160 V. This
condition could exist for up to five seconds (the max. allowed fault
clearance time for fixed equipment circuits) and the danger of that in a
wet-body situation should be obvious.

Feel free to shoot me down here, but I have just the same bonding
question. I have bonded all exposed metalwork together in the bathroom,
including to a cold water pipe. I don't particularly want to link into
any local circuits, I was going to take back to the TN-S earth point at
the CU.

Then you must be shot down in flames because what you are proposing
clearly violates the wiring regulations (BS 7671). Supplementary
bonding to exposed-conductive-parts (and therefore the CPCs) of
electrical equipment in a bathroom has been required since coming of the
14th edition of the IEE Regs (c. 1966). When the revised Section 601
(bathroom rules) came in to force in 2000 this was modified to require
bonding to the CPCs of *all* circuits feeding equipment within the
zones, _whether_or_not_ there are exposed-conductive-parts. Thus you
must still bond to the relevant CPCs, even if Class 2 equipment is
installed. This is clearly intended to provide for safety when
equipment is subsequently changed.

HTH
--
Andy

[Miketew]

Then you must be shot down in flames because what you are proposing
clearly violates the wiring regulations (BS 7671). Supplementary
bonding to exposed-conductive-parts (and therefore the CPCs) of
electrical equipment in a bathroom has been required since coming of the
14th edition of the IEE Regs (c. 1966). When the revised Section 601
(bathroom rules) came in to force in 2000 this was modified to require
bonding to the CPCs of *all* circuits feeding equipment within the
zones, _whether_or_not_ there are exposed-conductive-parts. Thus you
must still bond to the relevant CPCs, even if Class 2 equipment is
installed. This is clearly intended to provide for safety when
equipment is subsequently changed.

HTH
--
Andy[/quote]
You are of course dead right Andy, the only other thing is that all supplimentary equipotential bonding must be done in 6mmsq cable minimum and there are now special earth bonding clips for radiators, baths etc.
finally unless you are a qualified electrician and have registered and been asessed under part P building regs you are breaking the law doing this anyway as bathrooms are clearly defined as risk areas.

Miketew wrote:

You are of course dead right Andy, the only other thing is that all
supplimentary equipotential bonding must be done in 6mmsq cable minimum

Wrong. 4mm^2 covers most requirements in bathrooms, and smaller sizes
can be used if mechanical protection is provided. Larger sizes are only
required if you're bonding two CPCs of =6mm^2, or one CPC of =10mm^2
to extraneous-conductive-parts. Table 10B in the OSG provides a useful
summary.

finally unless you are a qualified electrician and have registered and
been asessed under part P building regs you are breaking the law doing
this anyway as bathrooms are clearly defined as risk areas.

Wrong again, although a building notice is required for work in a
'special location' (which does include a bathroom, within the Zones).

--
Andy

[Miketew]

Then you must be shot down in flames because what you are proposing
clearly violates the wiring regulations (BS 7671). Supplementary
bonding to exposed-conductive-parts (and therefore the CPCs) of
electrical equipment in a bathroom has been required since coming of the
14th edition of the IEE Regs (c. 1966). When the revised Section 601
(bathroom rules) came in to force in 2000 this was modified to require
bonding to the CPCs of *all* circuits feeding equipment within the
zones, _whether_or_not_ there are exposed-conductive-parts. Thus you
must still bond to the relevant CPCs, even if Class 2 equipment is
installed. This is clearly intended to provide for safety when
equipment is subsequently changed.

HTH
--
Andy[/quote]

The min supplementary bonding cable is 6mm sqd now.

Miketew wrote:

The min supplementary bonding cable is 6mm sqd now.

If so, where is this published?

David

Lobster wrote:

Miketew wrote:
The min supplementary bonding cable is 6mm sqd now.

If so, where is this published?

It isn't, he's wrong. Regulations 547-03-xx and Table 10B in the OSG
stipulate 4mm^2, except as noted in my previous article. There has been
no change since the publication of the original 16th Edition in 1992.

--
Andy

[Miketew]

Originally Posted by Andy Wade

Lobster wrote:

Miketew wrote:
The min supplementary bonding cable is 6mm sqd now.

If so, where is this published?

It isn't, he's wrong. Regulations 547-03-xx and Table 10B in the OSG
stipulate 4mm^2, except as noted in my previous article. There has been
no change since the publication of the original 16th Edition in 1992.

--
Andy

Your right Andy I had glanced at 547-02-01 main equipotential not supplementary.