Some of my colleagues have a problem, in respect of maintaining earth/cpc provision while decommissioning some distribution systems which are almost 60 years old. You can imagine the conditions, and while a lot of the gear must be disconnected and scrapped, the basic system must remain operational for some time yet - and needs adequate earthing. The practicable option is to use the armouring of the supply cable, which is PILCSWA, 4 core, 0.0225 sq inch. We have an approximate measured dimension - but you can imagine the difficulty of doing that, and hence doubt over the accuracy. We can find some cable dimensions data, but nothing indicates the dimensions of the armouring.
Has anyone got anything tucked away which might help us?

Many thanks

Graham

I cant find any actual information, but I do know that earthing is seldom a problem with PILC cable. The lead sheath usually has a larger CSA than the armours and also has a lower resistivity. The two earth paths are in pararell further reducing the resistance
As a 0.0025 is just smaller than 16mm you require the minimum CSA of the protective conductor to be the same size as the phase (table 54.7)
If you can estimate the CSA of the steel and lead, you can use the formula in 543.1.3 along with the values in table 54.4 to give some comfort.