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RCD disconnection times on a TT system

Volt Hunter
Hi Guys, first post after a long time reading the forums.


I have a client questioning the disconnection times provided by a 30mA type A RCBO on a TT system, tripping times provided are 221ms at 30mA and below 40ms at 150mA.


It protects a 16A socket in an outdoor environment, so must comply with the disconnection time provided in Table 41.1 of BS7671 of 0.2 seconds

Looking at table 3A on page 363, that states that a 30mA RCD must trip within 300ms at 1x, which is obviously outside the limits above, and 40ms at 5x.


Can we state that because the 5x test trips at less than 40ms it complies with fault protection, or does the 30mA disconnection time also have to comply?


Thanks in advance for any guidance you can offer.
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  • 0
    How many times was it subject to test? Many times I have got +200ms on x1 or even no trip on first assault. Hit the test button a few times and then different results. If you have already done this then given your results, there is nothing to be concerned about.
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  • 0
    How many times was it subject to test? Many times I have got +200ms on x1 or even no trip on first assault. Hit the test button a few times and then different results. If you have already done this then given your results, there is nothing to be concerned about.
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