If the house has an underground metal sheathed supply cable would the DNO not be willing to clamp the earth tail to it? That seems like the best option the earth loop will be very low impedance I can't think 8f a better earth in those conditions. I do wonder why that hasn't been done anyway for all the houses unless its been converted from OH lines at some time
They might, but it is DNO dependant, and the history of cables varies. Not all lead cables, especially early ones, are actually connected at the transformer end and at every buried joint in the way that would carry the full prospective fault without failures.. In such cases, the armour may be at earth potential more or less, but still not safe to be used as the earth electrode.
You do see odd water pipe earthing clamps on lead mains, and sometimes the DNO do put them there themselves, sometimes they appear by magic, though more common now is a spiral 'constant force' spring, thingy, like the mutant offspring of the clockwork spring and the dangerous bit from a corned beef can - think cut fingers and a lot of spring force.
however, sometimes the DNO will say it cannot carry fault currents and declare it to be underground TT, When combined with cast iron incomers, and the lead mains can be that era, then you have a metal cased company fuse with no reliable earth. At that point a few phone calls are needed to get a new cut out.
If the house has an underground metal sheathed supply cable would the DNO not be willing to clamp the earth tail to it? That seems like the best option the earth loop will be very low impedance I can't think 8f a better earth in those conditions. I do wonder why that hasn't been done anyway for all the houses unless its been converted from OH lines at some time
They might, but it is DNO dependant, and the history of cables varies. Not all lead cables, especially early ones, are actually connected at the transformer end and at every buried joint in the way that would carry the full prospective fault without failures.. In such cases, the armour may be at earth potential more or less, but still not safe to be used as the earth electrode.
You do see odd water pipe earthing clamps on lead mains, and sometimes the DNO do put them there themselves, sometimes they appear by magic, though more common now is a spiral 'constant force' spring, thingy, like the mutant offspring of the clockwork spring and the dangerous bit from a corned beef can - think cut fingers and a lot of spring force.
however, sometimes the DNO will say it cannot carry fault currents and declare it to be underground TT, When combined with cast iron incomers, and the lead mains can be that era, then you have a metal cased company fuse with no reliable earth. At that point a few phone calls are needed to get a new cut out.
