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Maximum ZS exceeded

Newfutile

i am testing in some flats which has cleaners sockets (in communal areas) wired as a ring final.

these have C32 rcbo circuit protection.

i have measured 1.0 ohm ZS on the 4th floor sockets, maximum zs (80% OSG) would be 0.54 ohm.

as its a rcbo this meets ADS for earth fault current via the rcd part of the rcbo.

if we assume the neutral is the same as cpc (its probably not) this will take over 5 seconds for a line to neutral fault as only 230 amps will flow, a C32 needs 320 amps to disconnect on the flat part of the curve.

we own the flats so its up to me to make any remedial repairs i deem required.

should i change the rcbo’s  for lower rated B curve type?

Do we even have line - neutral disconnection times? 

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    Newfutile said:
    as its a rcbo this meets ADS for earth fault current via the rcd part of the rcbo.

    Unless the RCBO is functionally dependent on line voltage with a classification of 'E2' or 'E3' according to Table Z1 of BS EN 61009-1:2010+A1:2012+A2:2013. See Table 6.3.4 of 2026 On-Site Guide, page 47, row that starts at left hand column 'characteristic' with 'Method of operation according to dependence on line voltage (Table Z1 of BS EN 61008-1 and Table Z1 of BS EN 61009-1)'

    If it's functionally dependent on line voltage and classified as E1 (or by  inference if there is no marking for line voltage dependence, then it must be line voltage independent ... but if it's a global product to IEC 61009-1 it might not have a marking even if it is line voltage dependent) these products can be used for ADS as well as additional protection.

    See this BEAMA guide: https://www.beama.org.uk/static/dda8f294-e43c-484f-8061e92b1f1e64e0/Technical-Bulletin-Guide-to-Residual-Current-Device-RCD-E-Marking.pdf 

    The guide also notes that some RCBOs on the market are currently marked 'E3' although the device might actually be suitable for both ADS and additional protection ... so probably best to check with the manufacturer.

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  • 0
    Newfutile said:
    as its a rcbo this meets ADS for earth fault current via the rcd part of the rcbo.

    Unless the RCBO is functionally dependent on line voltage with a classification of 'E2' or 'E3' according to Table Z1 of BS EN 61009-1:2010+A1:2012+A2:2013. See Table 6.3.4 of 2026 On-Site Guide, page 47, row that starts at left hand column 'characteristic' with 'Method of operation according to dependence on line voltage (Table Z1 of BS EN 61008-1 and Table Z1 of BS EN 61009-1)'

    If it's functionally dependent on line voltage and classified as E1 (or by  inference if there is no marking for line voltage dependence, then it must be line voltage independent ... but if it's a global product to IEC 61009-1 it might not have a marking even if it is line voltage dependent) these products can be used for ADS as well as additional protection.

    See this BEAMA guide: https://www.beama.org.uk/static/dda8f294-e43c-484f-8061e92b1f1e64e0/Technical-Bulletin-Guide-to-Residual-Current-Device-RCD-E-Marking.pdf 

    The guide also notes that some RCBOs on the market are currently marked 'E3' although the device might actually be suitable for both ADS and additional protection ... so probably best to check with the manufacturer.

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