SWA to workshop - 2 or 3 cores?

Hello
I've looked into how to rate the cable I need to supply my workshop and I will get someone in to help with working out the type of earthing that is best to use. The "run" will be about 50-75' (I'm measuring it later this week) and will be to supply power and lighting for single-phase duty (~ 3kW power plus a couple of strip lights). I'm happy to use online calculators to estimate correct sizing for permissible % drop under load. I think 4mm^2 will do it, from memory.
What I am unsure about is whether to use 2-core SWA and use the armouring as the earth, or go for three cores such that one of theose is the earth.
What's best practice?
Thanks
DDS
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and
that
later
theose is

No doubt I'll be howled down by the professionals, but for something at that distance from the house I've always exported the house earth on the third core (don't like steel conductors!) and also fitted an earth spike. So the third core and the steel wire armour are in parallel and an earth spike at the far end.
AWEM
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I have a feeling that the answer may depend on the type of earthing you are using.
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http://www.gadsolutions.biz/regulations/swa-as-the-cpc
has an interesting article.
However your size or erthing optionss may depend upon any main bonding that may need to be done in the workshop
--
Adam



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On 21/03/2011 23:42, DDS wrote:

OK, the long and detailed answer:
http://wiki.diyfaq.org.uk/index.php?title=Taking_electricity_outside
Short answer: for single phase, and where there is no need to export a PME equipotential zone, then 2 core.
One of the first things you need to know is your earthing system at the supply end:
http://wiki.diyfaq.org.uk/index.php?title rthing_Types
--
Cheers,

John.

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