TT earth question

The resistance of 20m of thick earth cable is negligible.

NT

Yes, you should do that. It is most unlikely that it will improve the earthing, as the water pipe, if copper/lead, will have a pretty low impedance to earth, however, you will comply with the Regs, as a water pipe, (if a public supply) cannot be used as an earthing conductor. The risk is that the water Company come along one day, put plastic pipe in, then suddenly you have no main earth. It is RCD protected isnt it? If not, get it done. VOELCB's are not adequate if it has one of those.

TT cannot be PME, but, it can be modified from TT to TN-C-S, if the Distributor makes the relevant connections on its network.

A photo of your electrical cut out may reveal the answer.

I know two posters that had PME supplies but did not know that until I looked at them:-)

It's easy not to know - and not just the customer. When our supply line was moved from posts to underground years ago, we were supposed to have PME. 2 men in a van, 2men in a cherry-picker and an inspector turned up to chenge something from the post before it was removed (ICR what - too long ago). Men came in looking puzzled, inspector, having had a good look at everything, realised that it was already PME!

A few years later the water supply became MDPE...!

(he spotted the corner of a PME sticker that had almost been buried under a pile of main cutout sealing stickers!)

Its unwise to rely on the water pipe since even if its a good earth now, you can't guarantee it will stay that way.

It may well be that at one time they did not support PME (hence all the TT installs) but then later upgraded the local distribution wiring to support it[1]. If you convert to PME, then you can leave you existing TT earth connected - it simply becomes another of the "multiple" earth connections.