High Ze on tncs system

mcm · Sep 11, 2011

Compleated a consumer unit change the other day and when testing the Ze I got a reading of 0.43, I know it should be 0.35 so what should i do?.

All the other readings was fine such as zs values, so should I compleate the certificate and make a note of the high Ze. Then phone the supplyer to investigate as it is down to them at the end of the day.

I checked all the connections and 0.43 was the best i could get.

Thanks.

telectrix · Sep 11, 2011

you've answered your own question. it's the DNO you need to contact, not necessarily the supplier. they 2 are often different.

Deleted member 26818 · Sep 11, 2011

What was the reading between L&N?

Richard Burns · Sep 12, 2011

I had a 0.42 reading the other day, rang the DNO and they were out and "fixed" it within two hours before I had finished 1st fix. Admittedly they only tightened the neutral connection but I have found they are responsive to these requests.
If you have completed the install then really you cannot sign off the certificate as the install does not meet BS7671 so you need the DNO to sort it first.

Risteard · Sep 12, 2011

Richard Burns said:
If you have completed the install then really you cannot sign off the certificate as the install does not meet BS7671 so you need the DNO to sort it first.

The DNO's equipment is outside the scope of BS 7671.

MarkieSparkie · Sep 12, 2011

Hi mcm, ensure your Ze reading is from a high current loop test (NOT No-Trip). If you are confident in your “high” reading, you should reconnect the main earthing conductor, replace any covers and ensure that the installation remains isolated and locked-off. Contact the DNO immediately; they will issue a priority call-out to the site because a potential PME fault may effect other installations in the area in addition to yours. In my area the DNO aim to respond within an hour of the call. You should not leave the site, as you will need to liaise with the DNO operative when he/she arrives. You should not complete the installation paper work at this point. The DNO operative will test your installation with their very high current EFLI tester if the reading is >0.35 ohms, he will carry out other tests/actions to find the fault and correct it. If on the other hand he finds EFLI is within the normal range < 0.35 ohms, you may be given either the measured value and the make; type; serial number of the instrument used or most operatives however will be less committal and just give you a maximum 0.35 ohms for the PME network. When the fault is corrected or you are told the installation is within the normal range, the DNO will give you permission to re-energise the installation, at which point you can continue testing. Record the value given and/or your new results on your installation paper work. I usually log the initial reading and my/DNO actions there after until permission to re-energise is given, as a contemporaneous note addendum to the report or certificate.