Hi all, we're involved in an almost complete rewire of a very old listed 1850s building. Most of the building is gutted, but 2 rooms are complete, and were rewired circa 2000 and the cables all look good and pass IR tests etc so will be put on separate RCBOs and so forth. That's not the reason for this post though, just background.
We noted on arrival that the supply is two single core PILC cables (it's Gosport, I've seen this a lot in the area, maybe it was common practice by the local undertaking back in the day). These are overall served with bitumen covered hessian and in conduit from the wall. The arrangement means phase and neutral are separate cables, so the service 'head' consists of a henley block for N, and a 100A fuse holder for L (with a 60A cartridge fitted, i confirmed this with the meter fitter).
There's a TN-S style earth clamp on the sheath of both cables together (the wrong kind of clamp but that's par for the course)... but there are two 'rogue' 4mm black wires coming from the N henley block. The post-meter connections go to a rat's nest henley 2 pole phase block that feeds various switchfuses and so on. The TN-S earth from the sheath goes to the main bonding terminal of a 60 amp switchfuse, and then (without a break) to the second 'piece of switchgear) (a 4 way wylex metal clad board).
Here is where the wtf-ness begins. The external earthing bolts of the wylex board are both used. One by the looped green conductor from the previous switchfuse, and the other by ONE of the 2 4mm blacks coming from the neutral block!
The other 4mm black disappears along with the tails into the innards of the 60A switchfuse which we haven't yet removed.
It's not worrying me overly much because we've been told by the meter operative to cut the seal on the neutral block and remove the offending black wires (he even left a nylon bung for the purpose of closing the vacated hole). He didn't seem overly concerned by the short between a supplier's neutral and earth on a TN-S system, despite my understanding that if there's a fault elsewhere in the neighbourhood, random currents might traverse the unfused 'shouldn't be there' cables?
There's been no recent major work on the mains in the area, so it's not likely to be TN-C-S in disguise... I am attaching pics of the incoming service area (prior to the meter change. The meter chap replaced the woefully undersized cables from the meter and installed an isolator.
Like I say this is just merely of interest rather than real worry as the existing installation boards will be removed, replaced with a modern RCBO board, and treated as true TN-C-S (obviously with Ze and PSCC readings taken and checked. The meter guy installed an isolator for us to make our job easier, then went off to see a pompey match.)
