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by olyjohn 418 days ago
Which is how grounding systems work in houses as well. Where I live, it's required code to have a 6 foot grounding rod driven into the ground, connected to your breaker panel. That's why modern houses in North America have 3 prong outlets instead of just 2.
1 comments
robocat 417 days ago
New Zealand household grounding legislation[1] also allows a long horizontal grounding wire, or connection to the reinforcing within concrete foundations.

I've only seen rods - likely the easiest solution but also maybe I've not had much exposure to newer builds.

Grounding in very dry areas is more tricky, so US legislation will likely be different in very dry areas - maybe requiring a maximum resistance and testing?

AFAIK in New Zealand neutral is not tied/bonded to earth at the house but only at the substation. That's to (1) avoid the house earth floating to mains voltage in a specific double fault situation (neutral return failed open circuit plus house earthing failure equals danger since the outside of metal appliances are usually earthed), and (2) avoid corrosion due to long term leakage currents. We've also got less tingly 240 Volts here.

I tried to search for some better info on earthing but only found an unreliable source that said:

  There is not one standard ground resistance threshold that is recognized by all agencies. However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less. The telecommunications industry has often used 5.0 ohms or less as their value for grounding and bonding.
[1] https://www.legislation.govt.nz/regulation/public/1997/0060/...
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robocat 407 days ago
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.
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