Outdoor RCD socket Trip

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An outdoor door socket with inbuilt RCD i installed trips the CU RCD when the test button is pressed on the socket. both are rated at 30ma, but I would of thought that the test button on the socket should not trip the CU RCD, Does this mean its a faulty Socket/RCD?
Also if the RCD trips in normal use, should this trip the CU RCD, as its the same rating?

Cheers
 
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It depends on how the trip button is connected, the normal RCD ones cause an imballance across L&N to trip the RCD. In this instance it should not trip downstream RCDs. However, unknowing how the manufacturer of your outdoor socket has connected the trip test I don't know. Some instances 2 30mA RCDs in series is unavoidable for example in caravan sites. Better to have 2 on an outdoor socket than none at all ;)
 
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As the test button on some just connects ingoing ph to outgoing N via a resistance to pass about 30mA then both RCDs carry test current.
It is possible that both will trip as you have found.

As said not very good discrimanation, however as also stated then 2 is better than none.

Do you feel a bit safer being protected by 2 devices witth a possible 7% failure rate rather than just 1 such device?
 
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As the test button on some just connects ingoing ph to outgoing N via a resistance to pass about 30mA then both RCDs carry test current.....

That setup shouldn't trip both RCDs . There would be no current imbalance either upstream or downstream of the device if the test button connected i/c phase to o/g neutral. the imbalance would just be at the local device.

If the test button connected a fairly high resistance earth to phase (or neutral) that would cause a current imbalance in the local device AND other devices upstream.
 
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If it is connected phase to earth then that will create a dangerous situation should there be a break in the CPC and the test button pressed, the main reason we must test EFLI before conducting an RCD test
(was one of the questions in the C&G2391 exam - a lot of people got wrong :eek: )
 
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