Following up on the recent thread about Earth Resistance measurements

[sophiecentaur]

Here in the USA

We are in different worlds and I need some advice which applies to a particular practical situation in UK.

I appreciate your input because of your high level technical knowledge but I need specific advice about what is approved over here in UK and how much I may have to pay. This whole issue is obviously a cloudy one and I say that because UKPN staff are reluctant to give me a definitive answer or opinion about T-T. Their answers would be loaded in terms of cost (to them in particular) so when they say something's acceptable it refers to economics and minimal safety considerations.

 

[Guineafowl]

Ok. I suspected as much. Here in the USA the transformer is seldom very far from the service panel. Several hundred feet at the most. There will be a ground rod at the transformer as well as one at the service panel for the residence. Two in a lot of cases because NEC says if the resistance is too high with one it needs to be two. This often translates into just put two in.
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In the UK I understand that distances are much farther between the transformer and the residence. It seems to me unless there are points along the run of cable feeding the residence that ground rods are installed, it wouldn't make a difference.
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The neutral is tied to the chassis of the meter box here in the USA as well as the main service panel. After the main service panel the ground (earth) are kept separate. Some places now require an emergency disconnect on the outside for fire department, etc. I'm not sure how that changes thing concerning where the earth and neutral split off.

Yes, I think we’re into ‘tomahto/tomayto” territory here. What you have is TN-C-S with extra earth rods at the installation end. You may not have N-E bonding along the power poles, but all those houses with rods would make it effectively a PME system.

Sometimes, TN-C-S supplies have ‘belt ‘n’ braces’ auxiliary earth rods here, and metal service pipes (gas, water) would be bonded to supply earth/neutral, effectively the same as a rod.

What you must also have is the lurking danger of the broken PEN/neutral. Older EV chargers had to be installed in their own TT island if in a TN-C-S property, but I gather the newer ones have neutral loss detection. But of course, that’s placing safety in the hands of electronics.

 

[sophiecentaur]

Again, there’s nothing really wrong with a TT earth. I had one for 8 years. Many consider it safer than TN-C-S (or N-E link, or MEN, depending where you are)* and opt to use it even today. For example, a distant outbuilding (too far out of equipotential zone) or EV charger.

My last house had an overhead supply and T-T earthing. Nobody died so nothing was "really wrong".

There are obviously a range of opinions about this and I won't lose too much sleep over it, whatever the outcome. But it annoys / worries me that my house (and everyone around me) may be served by a truly ancient network or, even worse, by a network which was 'up-graded a bit' without taking a good earth connection to all the houses.