[robocat]

Good comments on earthing in reply to this thread: https://forums.theregister.com/forum/all/2025/04/25/on_call/...

From comment about UK having three earthing standards:

  TT - Terre Terre or Earth/Earth, where the installation earth is actually connected directly to earth via an earth rod or similar and only phase and neutral run back to the transformer. Very common still with older housing stock, particularly with older overhead cables, though things are gradually being upgraded. The earth in a TT system is high impedance and unlikely to pass enough current to blow a fuse under fault conditions, so a separate safety device must also be fitted which these days is an RCD, and there are all sorts of rules for that

  TN-S - Terre Neutral - Separate, where the installation earth is connected to an earth installation at the transformer, where the neutral is also earthed. This earth is usually conducted over the metallic sheath of an underground cable and can blow fuses without the help of an RCD, though RCDs are mandated domestically for other reasons too

  TN-C-S - Terre Neutral - Combined - Separate, where the installation earth connects to the supply neutral at the service cutout of the installation (and nowhere else), while the neutral is grounded not just at the transformer, but for obvious safety reasons at several points along its path to your house too.