On 10/08/2013 21:14, Tim Watts wrote:
> [...]
> Essentially, if I stick a fork in that cable, I want the tool to hit mains-
> earth before it hits a live conductor.
Your fork or spade will almost certainly in contact with the soil when
it penetrates the cable and the loop impedance in the vast majority of
cases will be low enough to trip a 30 mA RCD in milliseconds. I agree
that it's a different matter for a non-RCD-protected circuit but even
then most digging implements have insulated handles.
> At times like these, I will happily exceed the regs if I'm unhappy with
> their strict application in a particular scenario. You may disagree in this
> case.
Fairynuff.
> But I think a residential garden having un-armoured cables buried direct in
> the ground is a very very bad idea.
Well, to be pedantic, almost every house has a service cable under the
front garden. These cables aren't armoured, but are of concentric or
lead sheathed construction. Time says these aren't a great hazard.
Moreover... how do you connect SWA to equipment underground? Crimped
resin-filled joints would be OK, but are expensive and would require the
equipment to be compatible. Burying SWA glands is surely a no-no, even
'CW' type. The gland makes the connection in the CPC, so has to be
accessible for inspection and testing [543.3.3 and 526.3]. The only
get-outs I can see are 526.3(i) - but SWA glands aren't designed to be
buried - or 526.3(v) - is there a relevant product standard? 543.3.1
also needs to be considered, re. corrosion - specifically the risk of
dezincification of a brass gland in some soils. NYY-J and plastic
glands seem more attractive now...
--
Andy