but again the DNO will not look at it which I think is obscene.

If it is a TN-C-S supply then describe the problem to the DNO in terms of voltage drop rather than Earth loop impedance - they're legally obliged to stay within ESQCR limits.

You could also point out that 0.28Ω is outside of most DNO's limit for EFLI for 200A (UKPN say 0.2Ω and WPD 0.22Ω for instance - there's probably a common Gxx document somewhere).

   - Andy.

https://www.nationalgrid.co.uk/downloads-view-reciteme/607407

National Grid earth loop impedance testing of services - acceptable values in section 3.0

This standard assumes most of the resistance is in the non current-carrying earth part of the loop. In this case a good tenth of an ohm is in at least one of the phase paths - and once loaded to 100A plus if it is a a problem of a single corroded point contact , something will be glowing in the dark. Power in 0.1 ohm at 100A is 1kW- that's like a small welder. !!

Again, I'd apply test loads and see if the LN voltage drop you would expect from that resistance is really observed (you may see something on the meter even with a kettle and or a few kW of heaters), if it is, that is a much bigger point to raise to justify remedial works than just the earth impedance  blowing a fuse in 8 or 9 seconds instead of 4 or 5 (regs fail but not an immediate danger).

Realise that the DNO will be approaching this in the same way Thames Water approach maintenance - they have miles of cables & thousands of transformers to look after, and they do the worst ones first. Also realise that any management that did not prioitize the best interests of the shareholders would be fired at the end of the financial year, so generally there is little appetite for doing upgrade work just in case, it has to wait until it is really needed.

Mike.

I agree it looks like there's a faulty joint somewhere, but how much time and resources will they allocate to tracing it?

I guess it all depends on the man on site - if they want to wriggle out of doing anything until there's a "real" problem they may on the basis that it's within limits, albeit significantly different from the other phases.

I agree it looks like there's a faulty joint somewhere, but how much time and resources will they allocate to tracing it?

I guess it all depends on the man on site - if they want to wriggle out of doing anything until there's a "real" problem they may on the basis that it's within limits, albeit significantly different from the other phases.