Am unable to post against the above original posting for some reason -
google refuses to retrieve the original message, so:

first many thanks to all posters for the advice: much appreciated &
has put me on course to get up to date on SWA.

Andy Wade commented:
-------

For 3-core the o/d for 6mm^2 is 17.0mm and for 16mm^2 it's 22.4mm (and
19.9mm for 10mm^2). [figures from Pirelli data sheet]

-----
Andy, please can you supply a pointer to this data sheet - I looked in
pirelli.co.uk but couldn't find a relevant table

looks to me that 16mmsq is getting a tad too large to handle: so am
thinking about10mmsq which will give a bit of rating leeway & it needs
to go into bare soil.

If I export the house earth using the 3rd 10mmsq conductor as earth
give an adequate earth? The alternative is to make the garage a TT
supply (with an earth rod) which implies all RCD & I'm not enthisastic
about that.

thanks again

"jim_in_sussex" wrote in message
om...
Am unable to post against the above original posting for some reason -
google refuses to retrieve the original message, so:

first many thanks to all posters for the advice: much appreciated &
has put me on course to get up to date on SWA.

Andy Wade commented:
-------

For 3-core the o/d for 6mm^2 is 17.0mm and for 16mm^2 it's 22.4mm (and
19.9mm for 10mm^2). [figures from Pirelli data sheet]

-----
Andy, please can you supply a pointer to this data sheet - I looked in
pirelli.co.uk but couldn't find a relevant table

looks to me that 16mmsq is getting a tad too large to handle: so am
thinking about10mmsq which will give a bit of rating leeway & it needs
to go into bare soil.

If I export the house earth using the 3rd 10mmsq conductor as earth
give an adequate earth? The alternative is to make the garage a TT
supply (with an earth rod) which implies all RCD & I'm not enthisastic
about that.

thanks again


It's best to have some RCD protection in the garage, with at least one light
that runs from a normal MCB breaker out with the RCD. The garage will be
the most likely place to use large power tools and things, so an RCD is
safer for this type of installation. You also shouldn't really transport
the earth from the house, as any trip off in the garage through an earth
conductor may also cause a trip off in the house supply as well. The earth
on the sub mains cable should be made through the armour, and an earth
conductor if you wish, but it is only to protect the cable running to the
garage if anyone hits it with a spade or pick axe.

Lurch has drawn my attention to a Clipsal Garage Consumer Unit which is an
ideal system for this type of power supply to an out building. A picture of
it he http://www.toolstation.com/messages.html?closeUp=82637 from the
toolstation website shows what you get.

BigWallop wrote:

safer for this type of installation. You also shouldn't really transport
the earth from the house, as any trip off in the garage through an earth
conductor may also cause a trip off in the house supply as well. The earth

What would be the mechanism for that? (Assuming the house is not wired
with an old ELCB)


--
Cheers,

John.

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jim_in_sussex wrote:

[Pirelli data]
Andy, please can you supply a pointer to this data sheet - I looked in
pirelli.co.uk but couldn't find a relevant table

Try
http://www.pirelli.co.uk/en_GB/cables_systems/energy/catalogue_pdf/lv_pdf/bs5467.pdf
and yes, their web site is truly abysmal.

looks to me that 16mmsq is getting a tad too large to handle: so am
thinking about10mmsq which will give a bit of rating leeway & it needs
to go into bare soil.

10mm^2 sounds about right to me.

If I export the house earth using the 3rd 10mmsq conductor as earth
give an adequate earth?

Yes, so far as conductor size is concerned (and the armour alone of a
2-core cable may well be adequate, but that would require calculation).
Remember that if you export the house earth (especially as you're on
PME) you must create an equipotential zone in the garage, which means
main-bonding any incoming service pipes or accessible metalwork that's
in contact with the ground. If the floor is dry and your work is mostly
internal then this is an acceptable solution, IMO. But if the garage
has a damp solid floor and/or you are likely to use portable equipment
of Class 1 (earthed, 3-core flex) construction outdoors from this supply
then the TT method is preferable.

The alternative is to make the garage a TT supply (with an earth rod)
which implies all RCD & I'm not enthisastic about that.

See above. Sockets in the garage will almost certainly fall under the
"likely to be used for portable equipment outdoors" heading, so must be
30mA RCD protected in any case.

--
Andy