Three-Phase Neutral/earth Query.

23 May 2009
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United Kingdom
Hi all. We moved from the UK to renovate an old farmhouse in the Czech Republic. As is usual in this very rural region of the country, the house is supplied with 3-phase (Aluminium cables) via pole-mounted overheads at 25Amps/phase max. The wiring in the house was ancient, as was the fuse-board etc, so we've re-wired throughout, balancing the consumer-unit 'load' of the house into three dedicated areas (i.e. one area per phase).

This week, we had the local National Grid men down to change the old overhead Aluminium supply to an underground (10mm Copper) cable to our house. We have an established earth-grid comprising four, deep-piled rods buried into damp ground around the house, which was tested and passed some time ago.

However, the National Grid man has wired their new incoming 4-core Copper cable to the meter-box, such that their neutral is also connected to our earth-rod assembly. Our consumer unit is wired three-phase, a neutral AND a separate earth (to our earth-rods). But he has now connected our separate earth to their neutral (in the meter-box).

Bearing in mind that the remaining overhead cables to our neighbours are pretty much decrepit, and that our neighbours are, shall we say, fairly rural in their expectations, should we be worrying about possible consequences/damage to our home via the neutral connection to what I perceived to be our protective earth system?

Any and all help very much appreciated.
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you mean they've provided you with 3phase TN-C-S?

Hi ColJack,

Understood. I'm looking at '2005_16_Autumn_Wiring_Matters' which gives a good pictorial representation of the TN-C-S system you mention. I was concerned that the chap might have done something out of the ordinary, but I see now that the practice is not unusual.

That said, would there have been any undesirable consequences had the man NOT connected the supply neutral to our existing earth-rod arrangment? Until we decided to have the over-heads removed and a new underground cable laid, the existing (ancient) supply was not connected to our earth system at all. The supply cables simply comprised 3 phases and neutral.

Many thanks for your help.