TN-C-S (PNB) versus TN-C-S (PME).

Or even TN-C-S vs TN-S with some service heads.

The new IET Amendment 4 model forms.

electrical.theiet.org/.../

There is the same choice of half a dozen earthing arrangements on the new installation certificate as well as on the Minor Works, instead of the three on the current certificates.

DO NOT connect the earthing conductor to this terminal unless ...

Do not connect it at all, or somewhere else? 

I get the feeling that we need to encourage the DNOs to provide more stickers like that, also with the fitted service fuse rating, 

Or a form with one further  option 

"we dunno"

Joking aside, it does matter, as the potential for diverted neutral currents in the earthing system is most significant  in the PME case and the other cases tell us what range of Zs to expect and if we need an incoming RCD.

M

The photo Graham commented on above.

That one clearly says it's TN-S ... but the installation should conform to PME requirements anyway ...

This is an example of service head equipment where it can be difficult to distinguish, illustrated in the latest 9th Ed OSG (2026):

gkenyon said:

That one clearly says it's TN-S ... but the installation should conform to PME requirements anyway ...

That is certainly the safe option.

Those nationalgrid notices are pretty shocking - there should be no spelling mistakes. Above all, surely it is not about connecting the earthing conductor, but connecting and energizing the installation.

As worded, it will leave some people wondering what to do next. TT the installation?

So, which box will you tick with this one?