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Ze of PCE (Code of practice for EESS)

Hugh Frater

I've upgraded the EESS at my off-grid property (new batteries, new inverter/charger/mppt), all up and running as expected and everything working as it should. An EICR is required, and the electrician performing the inspection and testing has raised an interesting point, how to complete the Ze test and what value to put down on the certificate.

The IET Guidance Note 3: Inspection & Testing, when referring to prosumers installations suggest that the Ze test should be taken with the distribution board isolated, and at the output terminals of the PCE (the inverter), but this will just give the impedance of the output stage of the inverter, currently around 5-6ohms. This value being a fail because the supply from the PCE to the distribution board is T-N-S and this requires a lower value.

Again from guidance note 3, from 643.7.3.1 note 1, B, point 2:

“For island mode: if applicable, verification of earth fault loop impedance is determined using measured (r1+r2) values, plus the manufacturer’s information regarding the value of Ze to be assumed for the EESS or the relevant PCE within it.”
All clear there, except I can't get this value from the manufacturer, I've asked and they've gone silent on me.
It has been suggested by another electrician that I've spoken to (who admits to not having extensive EESS experience) that I install another earth rod and make the system TT from the PCE to the distribution board, then anything <200ohms would 'technically' be a pass, but as the PCE and the distribution board are within 1m of each other, this seems a bit of a fudge when T-N-S is preferred according to the latest Code of Practice for EESS (an excellent publication btw, my copy arrived yesterday)...
Something interesting to discuss, how we move forward from here?
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  • 0

    Hi. I thought, given that your system operates entirely off-grid, it is essential to install an earth rod. Additionally, it is advisable to incorporate a 100 mA S-type RCD downstream of your Power Conversion Equipment if required for fault protection, obviously depending on earth loop impedance value.

  • 0 in reply to AMK

    I’m not saying make it a TT system, I’m talking about connecting the earth rod to the neutral earth link of your PCE. Your final circuits most probably then be protected by 30 mA RCDs.

  • 0 in reply to AMK

    Earth rod is connected to the MET, N-E link is made in the PCE (although code of practice states it should be in the distribution board). All circuits are on 30mA rcbo’s.

    Still doesn’t help with the original issue/question though.

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  • 0 in reply to AMK

    Earth rod is connected to the MET, N-E link is made in the PCE (although code of practice states it should be in the distribution board). All circuits are on 30mA rcbo’s.

    Still doesn’t help with the original issue/question though.

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