BS7671;2018 Minor works certificates.

As for the test that produces a 220ms for a final circuit on a TT system requiring a 0.2s disconnection time that is for once clear in 643.7.1 as it says, " The effectiveness of the automatic disconnection of the supply by RCDs shall be verified using a suitable test equipment according to BS EN 61557-6 to confirm that the relevant requirements of Chapter 41 are met, taking account of the operating characteristics of the device". So a 220ms time would not meet the requirements of Chapter 41 although it would meet the product standard. The same would apply to RCDs to the older BS 4293 standard.

220ms at 1x doesn't prove that that requirement has been met, but neither does it prove that it hasn't been either.


You could re-do the test at say 2x or higher (say using the 1x setting on the next range up, which would normally give you around 3x) which hopefully gives you a result within 200ms. Or you could do a 5x test (using the supply N rather than PE if Zs is a problem - as that verifies the effectiveness of the RCD itself just the same) and perhaps get a result below 150ms.


I think we have a problem though in that recording the time without recording what the test involved makes it all rather meaningless to anyone subsequently reading the schedule.


Or perhaps we take the attitude that if the RCD is within spec. for the tests we perform then it can be deemed to be operating correctly, so it's reasonable to presume it'll also operate within specification for other residual currents. After all we don't attempt to test any other component of the installation to anything like this degree.


   - Andy.

As for the test that produces a 220ms for a final circuit on a TT system requiring a 0.2s disconnection time that is for once clear in 643.7.1 as it says, " The effectiveness of the automatic disconnection of the supply by RCDs shall be verified using a suitable test equipment according to BS EN 61557-6 to confirm that the relevant requirements of Chapter 41 are met, taking account of the operating characteristics of the device". So a 220ms time would not meet the requirements of Chapter 41 although it would meet the product standard. The same would apply to RCDs to the older BS 4293 standard.

220ms at 1x doesn't prove that that requirement has been met, but neither does it prove that it hasn't been either.


You could re-do the test at say 2x or higher (say using the 1x setting on the next range up, which would normally give you around 3x) which hopefully gives you a result within 200ms. Or you could do a 5x test (using the supply N rather than PE if Zs is a problem - as that verifies the effectiveness of the RCD itself just the same) and perhaps get a result below 150ms.


I think we have a problem though in that recording the time without recording what the test involved makes it all rather meaningless to anyone subsequently reading the schedule.


Or perhaps we take the attitude that if the RCD is within spec. for the tests we perform then it can be deemed to be operating correctly, so it's reasonable to presume it'll also operate within specification for other residual currents. After all we don't attempt to test any other component of the installation to anything like this degree.


   - Andy.