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Posted By Topic: RCD trip times , what to do when it goes over 30ms

Jan 15 2019 21:05

I've just wired a new house and fitted the board with all new 40a 30ma RCDs. Some of my rcd trip times are coming back as 34 ms , but book says they have to trip in 30ms and 30mA. The sub circuits are not long by any means. Is this an acceptable test result to put on a COC and if not what do I do.

Jan 15 2019 21:25


Jan 15 2019 21:28

Oh 300 is it! Haha, Thanks :)

Jan 15 2019 21:38

Always do a pole continuity test as well to confirm that supply has been disconnected

Jan 16 2019 11:30

FTR, there is NO requirement to record ANY test results on a CoC. Or anywhere else, for normal work.
Some CoC forms provide space for test results for your convenience, but the space and layout is - in every case that I've seen - unsuitable for anything but the simplest job, and barely adequate even for those.

Recording test results may be a condition of contract, or you may just want to do it, but if so you really should be using a better form.

For RCDs in particular, there is NO requirement to test trip times at all. The requirement, in, is simply that the RCD's operation be tested, either by test button + confirmation of markings or by "test equipment" that does both ac and dc tests.
And the result specified in is "the RCD shall disconnect the supply".

So 'codaxx' is correct that you should check for disconnection of all poles required to be disconnected; and this applies regardless of your test method.
And unless your RCD tester can do a dc test, it isn't compliant with current wording. That said, I can see nothing wrong with confirming Type by checking marking, and doing only an ac test. Which could be by simple plug containing suitable resistor, as per Note 3.

Equally there's no good reason not to check the trip time. It's just that you don't have check it, let alone record it (outside of special cases such as medical).

As far as COCs go, the applicable requirement [ESR 66] is that they certify that the work was done "lawfully and safely"; which includes that "the testing required by these regulations has been satisfactorily completed".

Jan 24 2019 16:21

Have a look at ESR 24 Electrically unsafe RCDs

Jan 24 2019 17:36

That's a common misunderstanding.
All ESR 24 does is declare RCDs unsafe
if they don't meet the stated conditions. So if, in the course of our work, we find that an RCD breaches one of these rules, we would have to recognise the fact thatit's electrically unsafe. But the ESR does NOT impose any obligation to test RCDs whatsoever; so we DON'T have to go looking 'just in case". And you woin't find any other ESR that requires testing against ESR 24 either.

The real purpose of ESR 24 is simply to provide clarity. After all; RCDs are both DMRAs requiring SDoC (which points to laboratory tests for compliance with relevant manufacturing Standards); and also DHRAs, which must have an Approval from Worksafe before being sold / supplied.

The obligations to test are in other ESRs, each one carefully written. Eg; ESR 90: after doing work on an appliance, confirm safety i.a.w "5762". For installation work; it's ESR 63; which in turn points to ESRs 59 & 60; where the testing required is "in accordance with" particular cited Standards.

For most types of installation; that's i.a.w "3000"; and the tests prescribed in "3000" (Section 8) do NOT require testing trip time. In fact, the latest edition states that explicitly.

NOWHERE in ESRs or installation Standards is there ANY obligation placed on electrical workers to test ANY products; the testing required by installation Standards is ALL testing of our work (ie, the selection and installation of fittings). We DON'T test the fittings themselves, to product manufacturing standards.

sure we test cables for insulation resistance, but that's NOT in case of manufacturing defect; it';s to ensure we haven't damaged it during installation. SWe don't immerse IP-rated gear and then open it up to see how much water got in - we just check the label.
We check the label of RCDs as well, and depending on what we find (or don't find)we may have to do a d.c. test. But we DON'T have to test trip time. Instead we have to prove we've installed the RCD correctly, so that it actually DOES disconnect the circuit (as per 'required results'). Which is why it's OK to use the test button , or a simple plug-with-resistor, for the a.c. test.

There are some Standards that require trip-time tests for RCDs, eg "3012", "3760", and "3003". This relates mostly to in-service testing; the exception being "3003".