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Bonding Clamps etc.



 
 
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  #1  
Old March 7th 05, 06:59 PM
andrewpreece
external usenet poster
 
Posts: n/a
Default Bonding Clamps etc.

Hello Folks,
Looking at my earthing (TN-S) I see a 6mm2 earth wire come from the
service head thingy
to my CU, then another green 6mm2 earth wire exits the CU and dives below
the floorboards to clamp onto my lead water pipe.
Since I now have gas and central heating pipes which appear
unbonded ( except by secondary means ) I decided to bond them to the main
earth, but I have some questions that Googling didn't clear up.

(1) Can I use 6mm2 earth cable for the short runs from my gas and CH pipes
to the main earthing point?

(2) I have some BS951 clamps which are a puzzle to me: I thought that one
threaded the strap through the clamp and tightened the screw, which would
tighten up the clamp on the pipe, but what I
took to be the clamp section ( it has the earth terminal attached to it )
does not move at all when the screw is tightened ( yes I backed the locknut
off ). Two metal dimples in the main clamp section prevent it from
tightening on the pipe. I figured I was wrong about how they worked so just
pulled the strap tight and screwed the screw down to lock it, but it is well
nigh impossible to get the strap tight in this way - the clamp rotates and
so can't be giving a good connection. What am I doing wrong?

(3) I believe that it is unnecessary to run an earth cable to my bathroom
( which has no bonding at all ), and that merely bonding all the exposed
metal bits to each other with 4mm or protected 2.5mm cable is OK??????

(4) I understand that suplementary bonding is not required in anyother
situation, i.e. kitchens and toilets????

(5) I cannot fit all the new earth cables into the earthing block in my CU -
only one terminal is still available, so I bought a metal busblock (?) which
I intend to mount exposed on the board, alongside the CU, and I will bring
the main service head earth into that and then take all other earths out of
that block, i.e. to the CU, to the CH pipes, to the gas pipe etc.

thanks for any answers or observations,

Andy.


Ads
  #2  
Old March 7th 05, 09:12 PM
Andrew Gabriel
external usenet poster
 
Posts: n/a
Default

In article ,
"andrewpreece" writes:
Hello Folks,
Looking at my earthing (TN-S) I see a 6mm2 earth wire come from the
service head thingy


That sounds more like TN-C-S.
For TN-S, the earth conductor would come from the cable sheath
under the service head.

to my CU, then another green 6mm2 earth wire exits the CU and dives below
the floorboards to clamp onto my lead water pipe.


Your installation isn't up to current regs.
If you are going to do anything to the installation, you need
to bring the earthing up to current regs, which includes replacing
the existing earth bonding, based on how you have described it.

Since I now have gas and central heating pipes which appear
unbonded ( except by secondary means ) I decided to bond them to the main
earth, but I have some questions that Googling didn't clear up.

(1) Can I use 6mm2 earth cable for the short runs from my gas and CH pipes
to the main earthing point?


Service bonding should normally be 10mm2.
Main earth conductor to supplier's earth connection should be 16mm2.

(2) I have some BS951 clamps which are a puzzle to me: I thought that one
threaded the strap through the clamp and tightened the screw, which would
tighten up the clamp on the pipe, but what I
took to be the clamp section ( it has the earth terminal attached to it )
does not move at all when the screw is tightened ( yes I backed the locknut


The strap goes round the pipe and then through the slots which raise
it off the pipework a second time.
Pull the strap tight with pliers and bend it sharply where the
tail exits the bracket to stop it slipping back in. Then the screw
clamps onto the strap, deforming in the bracket and pulling it
tight on the pipe. The screw should not touch the pipe itself, nor
deform the strap enough that it is pushed back onto the pipe under
the bracket -- if it does, you didn't pull it tight enough to start
with or it slipped back through the bracket before you got it tight.
Once you've used a clamp, the strap is deformed and cannot be reused.

(3) I believe that it is unnecessary to run an earth cable to my bathroom
( which has no bonding at all ), and that merely bonding all the exposed
metal bits to each other with 4mm or protected 2.5mm cable is OK??????


Yes. It should be connected to an earthing terminal in the bathroom
(ideally the earths of all circuits in the bathroom), but does not
need a dedicated run back to your main earthing terminal.

(4) I understand that suplementary bonding is not required in anyother
situation, i.e. kitchens and toilets????


Only in rooms containing a bath or shower.
Personally, I also do it within 2-3m of the kitchen sink too, but
this is not done by everyone, not a requirement, and not always held
to be a good idea either.

(5) I cannot fit all the new earth cables into the earthing block in my CU -
only one terminal is still available, so I bought a metal busblock (?) which
I intend to mount exposed on the board, alongside the CU, and I will bring
the main service head earth into that and then take all other earths out of
that block, i.e. to the CU, to the CH pipes, to the gas pipe etc.


That's fine. You need 16mm2 from the supplier's earth to this
terminal, and into the CU. The other bonding can normally be 10mm2.

--
Andrew Gabriel
  #3  
Old March 7th 05, 09:54 PM
andrewpreece
external usenet poster
 
Posts: n/a
Default


"Andrew Gabriel" wrote in message
...
In article ,
"andrewpreece" writes:
Hello Folks,
Looking at my earthing (TN-S) I see a 6mm2 earth wire come from

the
service head thingy


That sounds more like TN-C-S.
For TN-S, the earth conductor would come from the cable sheath
under the service head.


Thanks Andy. I understood that TN-S is most common for urban houses, and
that there would
most probably be a sign saying so if it was PME (TN-C-S ). I can't
immediately see why if the sheathed cable enters the service head/cutout
that means it's TN-C-S. Is there a foolproof way to tell?

to my CU, then another green 6mm2 earth wire exits the CU and dives

below
the floorboards to clamp onto my lead water pipe.


Your installation isn't up to current regs.
If you are going to do anything to the installation, you need
to bring the earthing up to current regs, which includes replacing
the existing earth bonding, based on how you have described it.


I had a feeling someone would say that :-(

Since I now have gas and central heating pipes which appear
unbonded ( except by secondary means ) I decided to bond them to the

main
earth, but I have some questions that Googling didn't clear up.

(1) Can I use 6mm2 earth cable for the short runs from my gas and CH

pipes
to the main earthing point?


Service bonding should normally be 10mm2.
Main earth conductor to supplier's earth connection should be 16mm2.


I've read conflicting stuff about this - some say the size of service
bonding depends on the earthing type in question. 16mm2 is out of the
question - the CU won't take 16mm2 nor will the brass earth terminal on the
service head: you're going to say now I should get the 'lectric company in
to replace my service head........ :-(

(2) I have some BS951 clamps which are a puzzle to me: I thought that

one
threaded the strap through the clamp and tightened the screw, which

would
tighten up the clamp on the pipe, but what I
took to be the clamp section ( it has the earth terminal attached to

it )
does not move at all when the screw is tightened ( yes I backed the

locknut

The strap goes round the pipe and then through the slots which raise
it off the pipework a second time.
Pull the strap tight with pliers and bend it sharply where the
tail exits the bracket to stop it slipping back in. Then the screw
clamps onto the strap, deforming in the bracket and pulling it
tight on the pipe. The screw should not touch the pipe itself, nor
deform the strap enough that it is pushed back onto the pipe under
the bracket -- if it does, you didn't pull it tight enough to start
with or it slipped back through the bracket before you got it tight.
Once you've used a clamp, the strap is deformed and cannot be reused.


I figured pulling the strap tight with pliers might work. However, the screw
does not deform the strap
pulling it tight. The strap sits in the U portion of a metal stamping shaped
thus:- U , which is held in position by the rest of the clamp. All that
happens when you tighten the screw is that the strap is clamped to the 'U'
and prevented from moving - it does not tighten at all, hence my
headscratching. All the tightening has to be provided by the initial pulling
the strap tight, and neither with fingers nor pliers does this result in a
good connection.

Am I to understand that the clamp as purchased has to be disassembled ( with
a bit of grunting I can pull out the U shaped bit and reassemble the clamp
so the U shaped bit is free to move down under the action of the screw ( by
reinserting it in the slotted bit below the metal dimples ). I can see in
that way that the strap will be dragged down under the action of the screw
to eventually clamp the strapagainst the U shaped bit and the pipe. Why no
clues if that is the way it is supposed to work? It's like one of those Xmas
cracker puzzles. Will try it anyway.

(3) I believe that it is unnecessary to run an earth cable to my

bathroom
( which has no bonding at all ), and that merely bonding all the exposed
metal bits to each other with 4mm or protected 2.5mm cable is OK??????


Yes. It should be connected to an earthing terminal in the bathroom
(ideally the earths of all circuits in the bathroom), but does not
need a dedicated run back to your main earthing terminal.


What passes for an earthing terminal in a bathroom? I have no electrics in
my bathroom.

(4) I understand that suplementary bonding is not required in anyother
situation, i.e. kitchens and toilets????


Only in rooms containing a bath or shower.
Personally, I also do it within 2-3m of the kitchen sink too, but
this is not done by everyone, not a requirement, and not always held
to be a good idea either.


OK

(5) I cannot fit all the new earth cables into the earthing block in my

CU -
only one terminal is still available, so I bought a metal busblock (?)

which
I intend to mount exposed on the board, alongside the CU, and I will

bring
the main service head earth into that and then take all other earths out

of
that block, i.e. to the CU, to the CH pipes, to the gas pipe etc.


That's fine. You need 16mm2 from the supplier's earth to this
terminal, and into the CU. The other bonding can normally be 10mm2.


Hmm, as befroe, not physically possible with my main earth terminal and CU
accepting 6mm2
maximum AFAICS.

cheers,

Andy.


  #4  
Old March 7th 05, 10:41 PM
andrewpreece
external usenet poster
 
Posts: n/a
Default


Correction, I have determined my main earthing cable is 10mm2, not 6mm2 as I
said, and the main earth terminal could take a 16mm2, but the CU cannot. I
have plans to upgrade the CU so there is hope I could have 16mm2 main
earthing cables eventually, only I have to stick with 10mm2 for now, unless
I parallel two up.

I have just unscrewed the Bakelite cover where the main cable terminates,
and emerging from the main cable there is a sheathed red core, probably
35mm2 or some such, a skein of smaller twisted black insulated conductors,
which I take to be the neutrals, and 4 bare copper conductors, adding up to
16mm2 probably, going tothe main earth terminal.

I suspect this proves it to be a TN-S system then, as I appear to have a
discrete earth return in the cable.

Andy.


  #5  
Old March 7th 05, 10:42 PM
Stefek Zaba
external usenet poster
 
Posts: n/a
Default

andrewpreece wrote:
Hello Folks,
Looking at my earthing (TN-S) I see a 6mm2 earth wire come from the
service head thingy
to my CU, then another green 6mm2 earth wire exits the CU and dives below
the floorboards to clamp onto my lead water pipe.
Since I now have gas and central heating pipes which appear
unbonded ( except by secondary means ) I decided to bond them to the main
earth, but I have some questions that Googling didn't clear up.

(1) Can I use 6mm2 earth cable for the short runs from my gas and CH pipes
to the main earthing point?

6mmsq is undersized by current Regs thinking: the main earthing
conductor (from service-head-thingy to earthing block, and on to CU
earthing terminal) is s'posed to be 16mmsq, and the main bonding
conductors (to water, gas, CH and so on) to be 10mmsq. I'm not sure of
the contractual/legal position on fiddling with the earth connection
provided by your supply company, but ideally you'd want them to do the
6mmsq - 16mmsq upgrade rather than d-i-y, even for The Best Of Reasons
and with the Best Of Intentions. They may take the opportunity to turn
you into a TN-C-S (PME) installation while they're about it, as this is
the Modern Fashion (and does reduce the earth loop impedance, i.e. make
it yet more likely that fuses will blow nice and quickly in the event of
L-to-earth-conductor faults).

(2) I have some BS951 clamps which are a puzzle to me: I thought that one
threaded the strap through the clamp and tightened the screw, which would
tighten up the clamp on the pipe, but what I
took to be the clamp section ( it has the earth terminal attached to it )
does not move at all when the screw is tightened ( yes I backed the locknut
off ). Two metal dimples in the main clamp section prevent it from
tightening on the pipe. I figured I was wrong about how they worked so just
pulled the strap tight and screwed the screw down to lock it, but it is well
nigh impossible to get the strap tight in this way - the clamp rotates and
so can't be giving a good connection. What am I doing wrong?

On the what-I-take-to-be-totally-standard-pattern clamps I have... the
'clamp section' indeed doesn't move. You wrap the strap round the pipe
and under the end of the screw. As you tighten the screw down (yes, with
the locknut backed off ;-) the two sections of the strap - the captive
start and the part you just threaded through - both deform under
pressure from the screw, pulling the strap tight against the pipe. Since
there's not a great deal of movement, I find it useful to keep the loose
end of the strap pulled tight with pliers, by rolling the outside of
their jaws against the side of the clamp, until the screw's far enough
in for the strap to grip tight against the pipe. And you can't really
reuse the clamps - once the strap's bent in, especially the captive end,
it ain't going to spring back when you slacken off the screw. Other than
that - I can't offer any pearls, or even bits of frosted glass, of wisdom.

(3) I believe that it is unnecessary to run an earth cable to my bathroom
( which has no bonding at all ), and that merely bonding all the exposed
metal bits to each other with 4mm or protected 2.5mm cable is OK??????

That's about it. The bathroom stuff is all about *supplementary*
bonding, so that all the bits of metalwork which are capable of
introducing a potential are at the *same* potential. That it ends up
being earth potential is incidental (and in some circumstances
undesirable, even).

(4) I understand that suplementary bonding is not required in anyother
situation, i.e. kitchens and toilets????

You understand rightly. It's the wetness and nakedness (most
importantly, bare-footedness, though an electrocution path might pass
through any other parts of the skin which rest firmly against the
metallic items at differing potentials) of the
(immediately-post-)bathing body which are the main causes of the lowered
resistance which increases the risk of shock: so it's baths and showers
we care about. If you take your imitation of 'The Naked Chef'
overliterally, you may want to indulge in supplementary bondage around
your kitchen sink, but that's a matter of personal taste, rather than
strict regulation. (Quiet at the back there, Simpkins!)

(5) I cannot fit all the new earth cables into the earthing block in my CU -
only one terminal is still available, so I bought a metal busblock (?) which
I intend to mount exposed on the board, alongside the CU, and I will bring
the main service head earth into that and then take all other earths out of
that block, i.e. to the CU, to the CH pipes, to the gas pipe etc.

You done good: a separate earthing block is preferred practice, since it
makes testing of earth impedance easier. (Our reading today is from
section 4.10 of the On-Site Guide: the lord Cook spake thusly unto us,
"[whilst] the earthing bar is sometimes used as the main earthing
terminal; however, means must be provided in an accessible position for
disconnecting the earthing conductor to facilitate testing of the
earthing". For so requireth fivehundredandfortytwo-dash-ohfour-dash-ohtwo.

thanks for any answers or observations,

Y're welcome - Stefek
  #6  
Old March 7th 05, 10:44 PM
EricP
external usenet poster
 
Posts: n/a
Default

On Mon, 7 Mar 2005 20:54:16 -0000, "andrewpreece"
babbled like a waterfall and said:

I've read conflicting stuff about this - some say the size of service
bonding depends on the earthing type in question. 16mm2 is out of the
question - the CU won't take 16mm2 nor will the brass earth terminal on the
service head: you're going to say now I should get the 'lectric company in
to replace my service head........ :-(


This is ****ing me off. It sounds like we have roughly the same system
that was legal when the house was built in 1979.

Having done some replumbing, I thought I would bring it up to some
decent safety level, thinking it would simply be extending the 6mm
earth and clamping it to the pipes. I now have to consider a
completely new run of 10mm (Something like a small pipe) from the CU
to the gas main and on to the plumbing. problem is the old one is in
the wall for a lot of its travel, behind the staircase and impossible
to get at. I will probably not bother, the danger risk is minute as no
electric stuff is anywhere near the pipes.

I am informed there are good reasons for it but to have to replace an
annoying, but tolerable copper cable with something that could serve
as a lightening conductor is not on for a small house.




  #7  
Old March 7th 05, 10:58 PM
andrewpreece
external usenet poster
 
Posts: n/a
Default


"EricP" wrote in message
...
On Mon, 7 Mar 2005 20:54:16 -0000, "andrewpreece"
babbled like a waterfall and said:

I've read conflicting stuff about this - some say the size of service
bonding depends on the earthing type in question. 16mm2 is out of the
question - the CU won't take 16mm2 nor will the brass earth terminal on

the
service head: you're going to say now I should get the 'lectric company

in
to replace my service head........ :-(


This is ****ing me off. It sounds like we have roughly the same system
that was legal when the house was built in 1979.

Having done some replumbing, I thought I would bring it up to some
decent safety level, thinking it would simply be extending the 6mm
earth and clamping it to the pipes. I now have to consider a
completely new run of 10mm (Something like a small pipe) from the CU
to the gas main and on to the plumbing. problem is the old one is in
the wall for a lot of its travel, behind the staircase and impossible
to get at. I will probably not bother, the danger risk is minute as no
electric stuff is anywhere near the pipes.

I am informed there are good reasons for it but to have to replace an
annoying, but tolerable copper cable with something that could serve
as a lightening conductor is not on for a small house.


I'm glad to see I'm not the only one who struggles with 'doing the right
thing' but finds it
nearly impossible without tearing half the house to bits, when the
improvememt in safety is
largely unquantifiable anyway! And still I struggle on......

Andy.


  #8  
Old March 7th 05, 11:06 PM
andrewpreece
external usenet poster
 
Posts: n/a
Default


"Stefek Zaba" wrote in message
news
andrewpreece wrote:
Hello Folks,
Looking at my earthing (TN-S) I see a 6mm2 earth wire come from

the
service head thingy
to my CU, then another green 6mm2 earth wire exits the CU and dives

below
the floorboards to clamp onto my lead water pipe.
Since I now have gas and central heating pipes which appear
unbonded ( except by secondary means ) I decided to bond them to the

main
earth, but I have some questions that Googling didn't clear up.

(1) Can I use 6mm2 earth cable for the short runs from my gas and CH

pipes
to the main earthing point?

6mmsq is undersized by current Regs thinking: the main earthing
conductor (from service-head-thingy to earthing block, and on to CU
earthing terminal) is s'posed to be 16mmsq, and the main bonding
conductors (to water, gas, CH and so on) to be 10mmsq. I'm not sure of
the contractual/legal position on fiddling with the earth connection
provided by your supply company, but ideally you'd want them to do the
6mmsq - 16mmsq upgrade rather than d-i-y, even for The Best Of Reasons
and with the Best Of Intentions. They may take the opportunity to turn
you into a TN-C-S (PME) installation while they're about it, as this is
the Modern Fashion (and does reduce the earth loop impedance, i.e. make
it yet more likely that fuses will blow nice and quickly in the event of
L-to-earth-conductor faults).


Hmmm. I'm thinking about leaving it all now, it's too much trouble for no
benefit.
Read my supplementary message where I correct myself, I think I have 10mm2,
not 6mm2 as I said. It's close enough for country work, ain't it!

(2) I have some BS951 clamps which are a puzzle to me: I thought that

one
threaded the strap through the clamp and tightened the screw, which

would
tighten up the clamp on the pipe, but what I
took to be the clamp section ( it has the earth terminal attached to

it )
does not move at all when the screw is tightened ( yes I backed the

locknut
off ). Two metal dimples in the main clamp section prevent it from
tightening on the pipe. I figured I was wrong about how they worked so

just
pulled the strap tight and screwed the screw down to lock it, but it is

well
nigh impossible to get the strap tight in this way - the clamp rotates

and
so can't be giving a good connection. What am I doing wrong?

On the what-I-take-to-be-totally-standard-pattern clamps I have... the
'clamp section' indeed doesn't move. You wrap the strap round the pipe
and under the end of the screw. As you tighten the screw down (yes, with
the locknut backed off ;-) the two sections of the strap - the captive
start and the part you just threaded through - both deform under
pressure from the screw, pulling the strap tight against the pipe. Since
there's not a great deal of movement, I find it useful to keep the loose
end of the strap pulled tight with pliers, by rolling the outside of
their jaws against the side of the clamp, until the screw's far enough
in for the strap to grip tight against the pipe. And you can't really
reuse the clamps - once the strap's bent in, especially the captive end,
it ain't going to spring back when you slacken off the screw. Other than
that - I can't offer any pearls, or even bits of frosted glass, of wisdom.


Everyone says the same thing - that the straps deform under the screw and
tightens on the pipe, but my straps don't deform at all, you can undo them
and
just see a faint circular scrape mark where the screw contacted the strap,
and that's
even if you apply an unfeasible amount of torque to the screw. Nor does the
strap
tighten even slighly, as there is no force acting on the strap which could
tighten it.
I am coming to believe that these clamps must be disassembled then
reassembled
in a different arrangement to that they were purchased in before they will
work. I
have pulled one apart and rearraged it and will test my theory tomorrow.

(3) I believe that it is unnecessary to run an earth cable to my

bathroom
( which has no bonding at all ), and that merely bonding all the exposed
metal bits to each other with 4mm or protected 2.5mm cable is OK??????

That's about it. The bathroom stuff is all about *supplementary*
bonding, so that all the bits of metalwork which are capable of
introducing a potential are at the *same* potential. That it ends up
being earth potential is incidental (and in some circumstances
undesirable, even).

(4) I understand that suplementary bonding is not required in anyother
situation, i.e. kitchens and toilets????

You understand rightly. It's the wetness and nakedness (most
importantly, bare-footedness, though an electrocution path might pass
through any other parts of the skin which rest firmly against the
metallic items at differing potentials) of the
(immediately-post-)bathing body which are the main causes of the lowered
resistance which increases the risk of shock: so it's baths and showers
we care about. If you take your imitation of 'The Naked Chef'
overliterally, you may want to indulge in supplementary bondage around
your kitchen sink, but that's a matter of personal taste, rather than
strict regulation. (Quiet at the back there, Simpkins!)

(5) I cannot fit all the new earth cables into the earthing block in my

CU -
only one terminal is still available, so I bought a metal busblock (?)

which
I intend to mount exposed on the board, alongside the CU, and I will

bring
the main service head earth into that and then take all other earths out

of
that block, i.e. to the CU, to the CH pipes, to the gas pipe etc.

You done good: a separate earthing block is preferred practice, since it
makes testing of earth impedance easier. (Our reading today is from
section 4.10 of the On-Site Guide: the lord Cook spake thusly unto us,
"[whilst] the earthing bar is sometimes used as the main earthing
terminal; however, means must be provided in an accessible position for
disconnecting the earthing conductor to facilitate testing of the
earthing". For so requireth fivehundredandfortytwo-dash-ohfour-dash-ohtwo.

thanks for any answers or observations,

Y're welcome - Stefek


thanks,

Andy.


  #9  
Old March 7th 05, 11:21 PM
Steven Briggs
external usenet poster
 
Posts: n/a
Default

While we're on earth clamps, whats the preferred method of dealing with
the embossed aluminium safety labels with a slot at both ends?
a) Leave both ends captive on the strap round the pipe (but label is too
long for 15mm pipe)
b) Leave one end captive & the other flapping in the breeze.
c) Trap it onto the free end of the strap (by folding the spare strap)?
d) Toss it in the bin (Noooo!)


--
steve
  #10  
Old March 7th 05, 11:33 PM
Andrew Gabriel
external usenet poster
 
Posts: n/a
Default

In article ,
"andrewpreece" writes:

"Andrew Gabriel" wrote in message
...
In article ,
"andrewpreece" writes:
Hello Folks,
Looking at my earthing (TN-S) I see a 6mm2 earth wire come from the
service head thingy


That sounds more like TN-C-S.
For TN-S, the earth conductor would come from the cable sheath
under the service head.


Thanks Andy. I understood that TN-S is most common for urban houses, and
that there would
most probably be a sign saying so if it was PME (TN-C-S ). I can't
immediately see why if the sheathed cable enters the service head/cutout
that means it's TN-C-S. Is there a foolproof way to tell?


Look at the FAQ: http://www.diyfaq.org.uk/electrical/...al.html#system

Service bonding should normally be 10mm2.
Main earth conductor to supplier's earth connection should be 16mm2.


I've read conflicting stuff about this - some say the size of service
bonding depends on the earthing type in question.


It does. I gave you the figures which cover most residential
installations. In theory, your supplier can ask for larger
conductors in some cases too.

16mm2 is out of the
question - the CU won't take 16mm2 nor will the brass earth terminal on the
service head: you're going to say now I should get the 'lectric company in
to replace my service head........ :-(


I don't think I've seen such a service head, except possibly a 5A
one in the base of a streetlamp column. Does this or the CU have
multiple terminals -- if so you can split the conductor strands
into two terminals. Otherwise, I guess you're stuck with using
10mm2, which is probably OK if you only have a 60A cutout.

(2) I have some BS951 clamps which are a puzzle to me: I thought that one
threaded the strap through the clamp and tightened the screw, which would
tighten up the clamp on the pipe, but what I
took to be the clamp section ( it has the earth terminal attached to it )
does not move at all when the screw is tightened ( yes I backed the locknut


The strap goes round the pipe and then through the slots which raise
it off the pipework a second time.
Pull the strap tight with pliers and bend it sharply where the
tail exits the bracket to stop it slipping back in. Then the screw
clamps onto the strap, deforming in the bracket and pulling it
tight on the pipe. The screw should not touch the pipe itself, nor
deform the strap enough that it is pushed back onto the pipe under
the bracket -- if it does, you didn't pull it tight enough to start
with or it slipped back through the bracket before you got it tight.
Once you've used a clamp, the strap is deformed and cannot be reused.


I figured pulling the strap tight with pliers might work. However, the screw
does not deform the strap
pulling it tight. The strap sits in the U portion of a metal stamping shaped
thus:- U , which is held in position by the rest of the clamp. All that


Sorry, but I can't picture what you're doing wrong.
Can't find any web pictures to point you at either.

(3) I believe that it is unnecessary to run an earth cable to my bathroom
( which has no bonding at all ), and that merely bonding all the exposed
metal bits to each other with 4mm or protected 2.5mm cable is OK??????


Yes. It should be connected to an earthing terminal in the bathroom
(ideally the earths of all circuits in the bathroom), but does not
need a dedicated run back to your main earthing terminal.


What passes for an earthing terminal in a bathroom? I have no electrics in
my bathroom.


In that case, just bond.

--
Andrew Gabriel
 




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