I've replaced an overhead supply to a shed with a buried SWA cable. The
shed has an earth spike so grounding the SWA at the (PME) head end is
only to protect the cable - where can I find a spec for the size of the
grounding wire that connects the SWA shield to the main earth?

On 28/06/2018 22:02, wrote:

I've replaced an overhead supply to a shed with a buried SWA cable. The
shed has an earth spike so grounding the SWA at the (PME) head end is
only to protect the cable - where can I find a spec for the size of the
grounding wire that connects the SWA shield to the main earth?

Calculate the prospective fault current on the feed cable to the SWA,
then use the adiabatic equation to assess the minimum CSA for the earth
connection.

Details covered he

http://wiki.diyfaq.org.uk/index.php/...ub_main_design


--
Cheers,

John.

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On 28/06/2018 22:02, wrote:
I've replaced an overhead supply to a shed with a buried SWA cable. The
shed has an earth spike so grounding the SWA at the (PME) head end is
only to protect the cable - where can I find a spec for the size of the
grounding wire that connects the SWA shield to the main earth?

Same size as the cores of the cable and you cannot usually go wrong.

I assume that the only protection you are considering is a spade through
the SWA and that it should trip the head end MCB.

--
Adam

Presume you're using an insulated "break" gland at the shed end and the shed is forming a TT system? The RCD operating residual current will be low so the main consideration will be physical resilience hence affected by mechanical protection arrangements. It used to be tabulated as MINIMUM 2.5mm2 if protected or 4.0mm2 if not protected but other conditions apply if buried in soil/insulated/bare/copper/steel If you haven't got a copy of the current wiring regulations or "on site guide" try the local library.

Damn I misread the original post. I took the question as what size conductor from earth rod to MET in the shed TT system ˜¹

On 30/06/2018 23:13, Cynic wrote:
Damn I misread the original post. I took the question as what size conductor from earth rod to MET in the shed TT system ˜¹


And your answer, if that had been the question, was spot on:-)

--
Adam

On 28/06/2018 22:02, wrote:
I've replaced an overhead supply to a shed with a buried SWA cable. The
shed has an earth spike so grounding the SWA at the (PME) head end is
only to protect the cable - where can I find a spec for the size of the
grounding wire that connects the SWA shield to the main earth?

Thanks for all the responses - now sorted.