Ian Wells asks about than expected Ze readings with a TT electrical system. His question has been answered by the NICEIC (Theme – Electrical Testing):
Question: If I obtain higher than expected readings on my Ze results, especially on TT systems, do I just record the value anyway, or should I inform some electricity body? If so, who do I contact?
Answer: If you get readings above that which is expected on a TNS or TNCS installation, then you should inform your DNO for confirmation that your reading is correct and that it is not because of a deteriorated or damaged supply cable.
However a TT arrangement should have a reading of below 200 ohms to be deemed stable, and ideally below 100 ohms.
You should read Note 2 below table 41.5 on page 50 of the current Wiring Regulations (BS7671) for further guidance.
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