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Is it my imagination or is this EICR a little odd?

Chris Pearson

Last week I had a look at a property which is up for auction, more as a matter of curiosity than a serious investment, but it is charming and if only I were 10 years younger!

The EICR was published today. It wasn't a drive-by (only at 70 mph mind 'cos there is a speed camera right beside the house on the M27) because the stickers, dated 2020 were on the DBs (peak and off-peak).

The estimated age of the installation is 35 years, but the DBs looked very modern - all RCBO and clean.

TN-C-S aerial supply. Ze was given as 0.31 Ω. So why in the table below do some of the Zs add up, and some not?

Circuit R1+R2 Zs R1+R2+Ze Discrepancy
Lights down 0.99 1.79 1.30 0.49
Lights up 1.86 2.36 2.17 0.19
Sockets down 1.42 2.02 1.73 0.29
Sockets up 0.66 1.32 0.97 0.35
Cooker 0.83 1.63 1.14 0.49
Immersion heater 1.12 1.46 1.43 0.06
Cooker 0.75 1.06 1.06 0.00
Shower 0.44 0.89 0.75 0.14
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  • Might the apparent increase in the measured Zs also be due to the inductance of the RCBO coils; particularly if, as Mr. Jewsbury suggests, this has been measured using a low current (non-trip) instrument? Should this were the case, there remains an anomaly between the results for the two cooker circuits; are they both protected by RCBOs?

    Geoff

  • in reply to Geoff Lyons

    Possibly, however if inductance were the principle issue, surely 'lights up' and 'lights down' would have a similar impedance delta?

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  • in reply to Geoff Lyons

    Possibly, however if inductance were the principle issue, surely 'lights up' and 'lights down' would have a similar impedance delta?

Children
  • in reply to gkenyon

    Agreed. There’s always repeatability of measurements and variability between devices to consider; 300 milliohm difference between (presumably) similar devices does seem a lot though. I’ve been trawling my archive of test results to see if I can see a pattern, or get a feel for typical uplift values; that hasn’t helped me much since, where I have a measured Ze (high current) and R1+R2, I normally state Zs as the sum of these rather than a directly measured result which is so often at odds, especially when a non-trip setting is used.

    It would be interesting to know if anyone has measured inductance, or impedance (@ 50 Hz), results for a range of devices (or even just one).

    Geoff

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