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RCD testing for additional protection

Horace Horace

Hi all, im trying to get my head round this question if anyone can help. Amendment 2 no longer requires us to record  RCD x5 results; I understand this is due to manufacturers of type A RCD's utilising various test currents to achieve disconnection times, and that due to some meters not operating at these specific test currents many were returned as defective when they were okay, and it was the testing method at fault.

In the old 18th ed x5 tests operating within 0.04 s used to be recognised in an AC system (as well as other methods such as bonding ect) as providing additional protection. However, because we no longer need to verify this test, how can we be sure the RCD will offer this additional protection ?? The x1 test may fulfil the disconnection time of 0.4s for a TN system for example, but this test verif'ys fault protection only does it not ?. As an RCD is generally used for additional protection (in a domestic sense at least) then how can we be sure it offers additional protection without the x5 test ?

I realise the x5 tests on type A RCD's pose problems as mentioned above. Has it been decided then that if a 30mA RCD passes the x1 test then its more than likely to pass the x5 as well and so no need to verify ??  I cannot find a definite answer to this !

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    Thanks for the responses, what I deduce from them is -- if an 30mA RCD operates within 300 ms of a fault on a TN system then it satisfies the 0.4 second disconnection and touch voltage limits; a higher fault current would operate the RCD more quickly and therefore there is no need to test at a higher current. Does that sound right.

    @ Chris Pearsson, Carrying out the range of tests on the auto function might sound easier but may not provide a suitable value on the x5 test  (if your expecting below 40 ms) due to different manufacturers having differing x5 perameters; this is certainly the case for RCD's other than type AC, and the reason why the regs have changed to exclude x5 tests. And why I asked the question.

    @ aajewsbury, yes that is logical, it just doesn't immediately appear like a improved way of verifying a device by omitting a test. As you say we rely on MCB's without testing so why not rely on just 1 test (at both phase angles) for an RCD.

    Just to note that m not opposed to the changes and deletion of the x5 test, its just I couldn't get my head around why the test was omitted, but now I know why (I hope).

  • 0 in reply to Horace Horace
    Horace Horace said:
    @ Chris Pearsson, Carrying out the range of tests on the auto function might sound easier but may not provide a suitable value on the x5 test  (if your expecting below 40 ms) due to different manufacturers having differing x5 perameters; this is certainly the case for RCD's other than type AC, and the reason why the regs have changed to exclude x5 tests. And why I asked the question.

    First make sure that your MFT is set to type AC, or A, or WHY.

    Of course if, for some reason, an RCD passed the x1 test, but not x5, you have made life difficult for yourself.

  • 0 in reply to Chris Pearson

    I was led to believe the omission of  x5 tests from am2 was due to the certain types of  RCD not responding to x5 tests in under 40ms due to the manufacturers design. x5 test parameters of certain types of RCD can be different according to manufacturer (Hager type A RCDs were a case in point); these different test parameters of the manufacturers were at odds with some standard UK meters which led to the return of many RCD's to the manufacturers as defective when in fact they were okay, and it was the testing method at fault. I mean why omit the x5 test if its not an issue (which it is and is why they omitted it). Generally most electricians cannot afford the newest meter that performs all these tests for each different manufacturer. Just saying, might be wrong thou as its a tricky subject

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  • 0 in reply to Chris Pearson

    I was led to believe the omission of  x5 tests from am2 was due to the certain types of  RCD not responding to x5 tests in under 40ms due to the manufacturers design. x5 test parameters of certain types of RCD can be different according to manufacturer (Hager type A RCDs were a case in point); these different test parameters of the manufacturers were at odds with some standard UK meters which led to the return of many RCD's to the manufacturers as defective when in fact they were okay, and it was the testing method at fault. I mean why omit the x5 test if its not an issue (which it is and is why they omitted it). Generally most electricians cannot afford the newest meter that performs all these tests for each different manufacturer. Just saying, might be wrong thou as its a tricky subject

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