hi all,

should i go for 2 or 3 core swa down to my garage? its about 40 meters away
and i am going for 16mm3

cheers

steve

John Rumm wrote:
On 18/05/2011 11:26, John Rumm wrote:
On 18/05/2011 09:09, Mr Sandman wrote:
hi all,

should i go for 2 or 3 core swa down to my garage? its about 40
meters away and i am going for 16mm3

Two, unless you are exporting a PME earth as well (and hence the main
bonding conductor).

Pardon me talking to myself, but its just been pointed out to me that
you were talking about 16mm^2 SWA. The armour on that has enough
copper equivalent CSA to be used as a main bonding conductor as well
- so you will only need two core regardless.

http://wiki.diyfaq.org.uk/index.php?...ricity_outside


Sorry John, I was working when I pointed that out to you and I needed to
check before posting to the newsgroup.


I would say a 16mm two core is fine for a 40m run using a 40A MCB. This
should cover voltage drop for a lighting circuit in the garage and allow any
mains bonding in the garage to meet the regs.


--
Adam

In article ,
says...

John Rumm wrote:
On 18/05/2011 11:26, John Rumm wrote:
On 18/05/2011 09:09, Mr Sandman wrote:
hi all,

should i go for 2 or 3 core swa down to my garage? its about 40
meters away and i am going for 16mm3

Two, unless you are exporting a PME earth as well (and hence the main
bonding conductor).

Pardon me talking to myself, but its just been pointed out to me that
you were talking about 16mm^2 SWA. The armour on that has enough
copper equivalent CSA to be used as a main bonding conductor as well
- so you will only need two core regardless.

http://wiki.diyfaq.org.uk/index.php?...ricity_outside


Sorry John, I was working when I pointed that out to you and I needed to
check before posting to the newsgroup.


I would say a 16mm two core is fine for a 40m run using a 40A MCB. This
should cover voltage drop for a lighting circuit in the garage and allow any
mains bonding in the garage to meet the regs.

16mm2 armour is fine in copper equivalence terms to act as a cpc for
fault protection, but NOT to act as a main protective bonding conductor.
See note at bottom of 544.1.1. For bonding it is the equivalent
conductance that matters.
Regards
Bruce

Bruce Burnett wrote:
In article ,
says...

John Rumm wrote:
On 18/05/2011 11:26, John Rumm wrote:
On 18/05/2011 09:09, Mr Sandman wrote:
hi all,

should i go for 2 or 3 core swa down to my garage? its about 40
meters away and i am going for 16mm3

Two, unless you are exporting a PME earth as well (and hence the
main bonding conductor).

Pardon me talking to myself, but its just been pointed out to me
that you were talking about 16mm^2 SWA. The armour on that has
enough copper equivalent CSA to be used as a main bonding conductor
as well - so you will only need two core regardless.

http://wiki.diyfaq.org.uk/index.php?...ricity_outside


Sorry John, I was working when I pointed that out to you and I
needed to check before posting to the newsgroup.


I would say a 16mm two core is fine for a 40m run using a 40A MCB.
This should cover voltage drop for a lighting circuit in the garage
and allow any mains bonding in the garage to meet the regs.

16mm2 armour is fine in copper equivalence terms to act as a cpc for
fault protection, but NOT to act as a main protective bonding
conductor. See note at bottom of 544.1.1. For bonding it is the
equivalent conductance that matters.
Regards

The CSA of the armour of a 2 core 16mm SWA cable is 42mm^2.
That gives it the copper equivalent of 18.6mm^2.

For most domestic installations that will be fine.

--
Adam

In article ,
says...

Bruce Burnett wrote:
In article ,
says...

John Rumm wrote:
On 18/05/2011 11:26, John Rumm wrote:
On 18/05/2011 09:09, Mr Sandman wrote:
hi all,

should i go for 2 or 3 core swa down to my garage? its about 40
meters away and i am going for 16mm3

Two, unless you are exporting a PME earth as well (and hence the
main bonding conductor).

Pardon me talking to myself, but its just been pointed out to me
that you were talking about 16mm^2 SWA. The armour on that has
enough copper equivalent CSA to be used as a main bonding conductor
as well - so you will only need two core regardless.

http://wiki.diyfaq.org.uk/index.php?...ricity_outside


Sorry John, I was working when I pointed that out to you and I
needed to check before posting to the newsgroup.


I would say a 16mm two core is fine for a 40m run using a 40A MCB.
This should cover voltage drop for a lighting circuit in the garage
and allow any mains bonding in the garage to meet the regs.

16mm2 armour is fine in copper equivalence terms to act as a cpc for
fault protection, but NOT to act as a main protective bonding
conductor. See note at bottom of 544.1.1. For bonding it is the
equivalent conductance that matters.
Regards

The CSA of the armour of a 2 core 16mm SWA cable is 42mm^2.
That gives it the copper equivalent of 18.6mm^2.

For most domestic installations that will be fine.

I agree it gives a copper equivalence in K terms which includes specific
heat. That is relevant for temperature rise in the adiabatic equation
in relation to sizing a cpc. But that is the wrong equivalence for a
bonding conducter which has to be done in pure conductance terms. I
said above it was at the bottom of 544.1.1, it is actually at the bottom
of Table 54.8 immediately below that regulation.

You need to be around 70mm2 cable before the armour reaches an
equivalence of 10mm2 copper in conductance terms.

Regards
Bruce

BruceB wrote:
In article ,
says...

Bruce Burnett wrote:
In article ,
says...

John Rumm wrote:
On 18/05/2011 11:26, John Rumm wrote:
On 18/05/2011 09:09, Mr Sandman wrote:
hi all,

should i go for 2 or 3 core swa down to my garage? its about 40
meters away and i am going for 16mm3

Two, unless you are exporting a PME earth as well (and hence the
main bonding conductor).

Pardon me talking to myself, but its just been pointed out to me
that you were talking about 16mm^2 SWA. The armour on that has
enough copper equivalent CSA to be used as a main bonding
conductor as well - so you will only need two core regardless.

http://wiki.diyfaq.org.uk/index.php?...ricity_outside


Sorry John, I was working when I pointed that out to you and I
needed to check before posting to the newsgroup.


I would say a 16mm two core is fine for a 40m run using a 40A MCB.
This should cover voltage drop for a lighting circuit in the garage
and allow any mains bonding in the garage to meet the regs.

16mm2 armour is fine in copper equivalence terms to act as a cpc for
fault protection, but NOT to act as a main protective bonding
conductor. See note at bottom of 544.1.1. For bonding it is the
equivalent conductance that matters.
Regards

The CSA of the armour of a 2 core 16mm SWA cable is 42mm^2.
That gives it the copper equivalent of 18.6mm^2.

For most domestic installations that will be fine.

I agree it gives a copper equivalence in K terms which includes
specific heat. That is relevant for temperature rise in the
adiabatic equation in relation to sizing a cpc. But that is the
wrong equivalence for a bonding conducter which has to be done in
pure conductance terms. I said above it was at the bottom of
544.1.1, it is actually at the bottom of Table 54.8 immediately below
that regulation.

You need to be around 70mm2 cable before the armour reaches an
equivalence of 10mm2 copper in conductance terms.

I get you.

With an 8 times greater resistivity for the steel than the copper then yes
it will need to be 70mm^2 2 core SWA (as that is where the armourings
reaches 80mm CSA)

--
Adam

On 20/05/2011 13:25, ARWadsworth wrote:
I get you.

With an 8 times greater resistivity for the steel than the copper then yes
it will need to be 70mm^2 2 core SWA (as that is where the armourings
reaches 80mm CSA)

Quite right - as debated previously at length both here and in the IET
forum. I do wonder whether it's what the committee intended to say
though, or whether it's just badly worded.

After all there's no upper limit allowed on the resistance of a copper
main bonding conductor, so why limit the conductance of a steel one?
Logically it should be either the adiabatic (I^2*t) capacity of the
conductor or its continuous current carrying capacity that should matter
for main bonding.

--
Andy

In article ,
says...

Logically it should be either the adiabatic (I^2*t) capacity of the
conductor or its continuous current carrying capacity that should matter
for main bonding.


I was wondering the same as neither maximum resistance nor maximum
length is specified. But I think it was probably deliberate because in
addition to adiabatic capacity and current withstand there is another
factor. The bonding is there to hold the touch voltage down during a
fault and hence the conductance/resistance of the bonding conductor
compared to say the cable introducing a fault is relevant.
Regards
Bruce

On 21/05/2011 09:35, BruceB wrote:

[...] The bonding is there to hold the touch voltage down during a
fault and hence the conductance/resistance of the bonding conductor
compared to say the cable introducing a fault is relevant.

Agreed, so why don't they stipulate a maximum resistance for copper main
bonding? There is a resistance limit for supplementary bonding of
course, fist introduced in the 16th ed., IIRC.

I can only imagine that it's a non-issue in practice, with the length in
practice unlikely to be enough to lead to an excessive resistance.
Large buildings will have larger capacity supplies, mandating larger
main bonding conductors. Supplementary bonding, OTOH, can be as small
as 1 mm^2 if incorporated in a cable or otherwise mechanically
protected, so the possibility of excessive resistance is more likely.

--
Andy

John Rumm wrote:


I am no fan of exporting PME earths and equipotential zones anyway in
most cases. So you would be better off making the far end TT and
sticking with two core SWA and isolating the earth at the far end IMHO.


It's a tricky issue. That solution is clean if you are doing a single
submain to a remote shed.

But what would be the best solution for running a lighting circuit round the
garden (gatepost lamps, couple of lamps in the garden sort of thing? The
same circuit might supply a small lamp in a bike shed and other odds and
sods. This would be a single supply circuit with local switching.

I suppose you could make everything class II and worry less (we'll assume an
RCD at the house end of the circuit source).

Or you could TT it - but if it goes to a variety of distant loads would you
have to stake it in several places?

What if it was desirable to use this circuit in the vicinity of another
circuit, eg in the workshop[1] so that if a power tool tripped the socket
circuit, the lights stayed on - you'd have to have the same earthing system
and cross bond them.

I'm still undecided on mine. My original plan was:

20A radial to a few waterproof sockets on the house wall (one on each
corner) - In theory a class I appliance *could* be plugged in outside from
this.

32A supply to workshop for sockets only (re point about tripping and lights
not going out as a result)

10A general lighting supply going all over the place including the workshop
(which would have a pair of DP isolators locally on point of entry)

This seemed like a good idea when I believed I had a TN-S earth, but got a
bit unravelled when the bloke proved EDF's records were wrong by opening up
the cutout housing (I actually have TN-C-S).

Thoughts appreciated

--
Tim Watt

In article , says...

(snip)
This seemed like a good idea when I believed I had a TN-S earth, but got a
bit unravelled when the bloke proved EDF's records were wrong by opening up
the cutout housing (I actually have TN-C-S).

Thoughts appreciated


I know I'll be at odds with some here, but I see very little problem
exporting TN-C-S earth. Or as I describe it extending the equipotential
zone. You do have to watch out on the bonding issue, but the likelihood
of a broken neutral coming into a house are vanishingly small UNLESS the
final few metres of cable is coming in overhead through trees into your
house. I watched my PME supply go in and the final earth electrode was
buried with the cable within a few metres of my house. So virtually
zero chance opf broken neutral in my case. Many believe there is a
general prohibition on exporting a TN-C-S earth. But that is a myth -
no such rule exists.

Regards
Bruce

In article ,
says...
Its interesting to note that they changed
the wiring style from four independent wires spaced vertically a few
inches apart, to an arrangement with all the wires twisted into a bundle
around a support wire. I presume the latter arrangement also makes
disconnection of the PEN conductor in isolation somewhat less likely.

known I think as ABC - aerial bunched conductor