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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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  • 0
    Newfutile said:
    these have C32 rcbo circuit protection

    Why?

    "Cleaners sockets" implies plugging in a vacuum cleaner, or perhaps floor polisher, for limited periods on an occasional basis. I doubt that there will be a whole army of cleaners operating together. So, the load should be moderate.

    I don't think that 1 ohm need be excessive, and of course it depends somewhat on the Ze/Zdb.

    I'd install a B32 or even B20.

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  • 0
    Newfutile said:
    these have C32 rcbo circuit protection

    Why?

    "Cleaners sockets" implies plugging in a vacuum cleaner, or perhaps floor polisher, for limited periods on an occasional basis. I doubt that there will be a whole army of cleaners operating together. So, the load should be moderate.

    I don't think that 1 ohm need be excessive, and of course it depends somewhat on the Ze/Zdb.

    I'd install a B32 or even B20.

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