The gasman calleth...

Never heard of the word "Riser" being used with a electrical supply. Think you meant Cut Out?

So he essentally put a link between the neutral of the armoured cable to an earth... essentially converting your supply to PME.

which earth did he attach to if it was not to your MET (main earthing terminal) and left your TT earthing in place.

No. He means riser.

'Riser' is common in commercial buildings (ie the duct from the basement to the roof that all your services go in).

It sounds like it was to the earthed sheath of the incomer, which would make it TNS. Which I'm a bit surprised about, that they didn't convert to PME. Or maybe there's a reason not to?

Maybe there's no harm to add TNS in the context of TT, but you can't do PME without disconnecting the TT?

Theo

So, in a shed supply then, which comes off a ring in the house. Could I earth the other end to a local earth rod if it was just the earth? I'm always a bit suspicious of the way people join up or not the neutral and earth in their meter cupboards. I also intend to generate an isolated mains supply through a transformer I have, which will allow the use of devices which have live chassis, and earth the chassis. We used to do a lot of this kind of thing for old analogue tv servicing. Brian

You can add a TT earth to a PME setup - it just becomes another of the "Multiple" earths.

(if you think about it, if you have metallic incoming services such as water or gas, and they are bonded to the main earth terminal as they should be, they are also acting as fortuitous additional parallel paths to earth in addition to the suppliers TN earth)

Perhaps the easiest understood is company fuse?

As I understand it (and happy to be corrected) PME isn't suitable for older street cabling. Perhaps too high an impedance to the substation where the neutral is earthed?

It basically a woven strap emerging from the incoming cable and taped over so I can't see how it's done. No sign of a clamp. With a hefty terminal mounted on the board the fuses are on. I'll take a pic later.

I think I was told the street wiring too old for this. When enquiring before.

I'm confused too. Earthing arrangements rather outside my pay grade.

I expected to see a clamp to the incoming cable armour. If so it doesn't show. And only took him minutes to fit.

Quite. Originally, the only earth here was to the incoming lead water pipe. It is still lead to the stopcock. All the house plumbing now copper. But an electrician pal measured it (ages ago) with his test gear and said it just fine. The gas pipe is iron barrel incoming (with plastic inside) and that is bonded to earth too.

Here's a pic of the earth they fitted:-

Dunno why they taped things up. They are coming to fit a new unit next Tuesday.

Maybe it was one of these under the tape:

That is your new MET (main earth terminal.)

So you now have a choice between using the supplier supplied MET or your own existing earth rods.

I'm sure Adam will be along in a bit to advise you of which is the best earthing option for you.

So it looks like you have a TN-S earth - although not actually connected to anything as yet.

There are still plenty of houses in London with no earth from the DNO - including one of my neighbours. I tried to persuade her to get a one, even offering first to upgrade her bonding for free. She wasn't interested. And she ain't stupid: maths graduate and head of a junior school. I couldn't kick off big time as my (admittedly long out of calibration) meter showed a Zs of 1.1 (and that was after they'd replaced the iron water main).

Sorry, I meant Ze

After Amndt 2 connection to earth by means of an electrode is recommended in addition to PME.

When I re-wired this house from scratch just after buying, in the 70s, fitted a CU with fuses. Just used the existing earth which passed tests at the time (the leccy board tested and approved the installation before connection, as well as removing a second meter in the house)

Much later I changed the CU to a split load type - one side RCD protected. And wanted the earth to conform to modern requirements. Leccy board wanted £600 to provide one, so went down the earth rod route. Had a pal at the time (now departed) who was a sparks and had all the test gear, so just did what he recommended.

But what they've provided isn't PME? As I understand it, PME isn't available with older supply cabling?