Tim Lane asks a question about testing a circuit and obtaining high Ze values. His question has been answered by the NICEIC (Theme – Regulations & Legislation):
Question: If I obtain higher than expected readings with my Ze results, especially on TT systems, do I just record the value anyway, or should I inform the electricity body?
If so, who should I contact?
Answer: If you obtain readings above expected on a TNS or TNCS installation, then you should be informing your DNO for confirmation that your reading is correct and that it is not because of a deteriorating or damaged supply cable. It is important that your local DNO confirms that this arrangement is adequate to ensure that it will continue to effectively offer an adequate earth fault path under ADS.
However a TT arrangement should have a reading of below 200 ohms to be deemed stable and ideally below 100 ohms.
It is also a requirement with BS7671:2008 that the earthing and bonding requirements including the suppliers equipment is safe and adequate, so you should read Note 2 below Table 41.5 on page 50 of the current Wiring Regulations - BS7671:2008 (2011) - for further guidance.
You should definitely get the situation resolved, or confirmed as adequate.
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