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18th question.

Former Community Member
Former Community Member
Hi all, any comments welcome on this one.
Is it still acceptable to have a socket outlet for a specific use not rcd protected under the 18th?
I fitted a single 13a socket outlet recently in a loft space for one of my regular customers, it is to supply a security camera system and the suppliers asked for a socket to be provided. It is supplied from the first floor lighting circuit which doesn't have rcd protection. (16th. ed. board) There is not the slightest chance of the socket being used to supply anything else and I would like to issue a mwc stating that the socket is only to be used for this specific purpose. If it's a major issue I could get back to the customer and arrange to fit an rcbo but I don't really think that is necessary? Thinking now about going back to change socket for an rcd protected one?
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    It should be noted as a final technical note, that SRCDs are not really an answer for fault protection (i.e. can't meet disconnection times) because they can't respond to an upstream fault. They can therefore only be used for additional protection



    Could you clarify that Graham? It sounds like you're saying that a SRCD/FCURCD might be too slow to provide the 0.4s or 0.2s disconnection required for ADS - which sounds rather odd to me (given they'd typically open in something like 40ms for most credible L-PE faults of negligible impedance). Naturally they can't provide protection from upstream faults - but then neither can any other protective device - faults on a distribution circuit imposing hazardous voltages for hazardous durations on downstream final circuits is a well known general problem - there's nothing peculiarly lacking in a BS 7288 device on that count.  A SRCD may rely on an upstream overcurrent protective device for backup protection in the case of large fault currents - but the same is true of DIN rail mounted RCCBs - they often have a breaking capacity not more than 3kA.


    Then there's the situation where Zs at the point where thee BS 7288 device is installed is fine for the upstream MCB, but the additional wiring downstream increases Zs beyond that limit (whether fixed wiring from a FCURCD or an extension lead from a SRCD) - are you suggesting that the BS 7288 device shouldn't be relied upon to provide ADS downstream - just additional protection - and so some other means of ensuring ADS downstream needs to be provided in addition?


       - Andy.
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    It should be noted as a final technical note, that SRCDs are not really an answer for fault protection (i.e. can't meet disconnection times) because they can't respond to an upstream fault. They can therefore only be used for additional protection



    Could you clarify that Graham? It sounds like you're saying that a SRCD/FCURCD might be too slow to provide the 0.4s or 0.2s disconnection required for ADS - which sounds rather odd to me (given they'd typically open in something like 40ms for most credible L-PE faults of negligible impedance). Naturally they can't provide protection from upstream faults - but then neither can any other protective device - faults on a distribution circuit imposing hazardous voltages for hazardous durations on downstream final circuits is a well known general problem - there's nothing peculiarly lacking in a BS 7288 device on that count.  A SRCD may rely on an upstream overcurrent protective device for backup protection in the case of large fault currents - but the same is true of DIN rail mounted RCCBs - they often have a breaking capacity not more than 3kA.


    Then there's the situation where Zs at the point where thee BS 7288 device is installed is fine for the upstream MCB, but the additional wiring downstream increases Zs beyond that limit (whether fixed wiring from a FCURCD or an extension lead from a SRCD) - are you suggesting that the BS 7288 device shouldn't be relied upon to provide ADS downstream - just additional protection - and so some other means of ensuring ADS downstream needs to be provided in addition?


       - Andy.
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