EV test

I can find no requirement to test the RDC-DD either in terms of tripping current or tripping time. I have looked at literature from several manufacturers for products that employ these devices but can find no reference for the need to test them. I am not suggesting that it wouldnt be prudent to conduct a test and it is clear that people like Megger in their new 1741A MFT obviously see a market for such a facility.

I don't think the product standard requires anything ... in fact, there are a number of options as to how the RDC-DD can be achieved, from integrated in a charge point or protective device, through stand-alone protective device, to a tripping device for mechanical linking to other protective devices.

The Megger 1741+ still requires a £420 accessory.

What exactly does the 1741 plus version do that the 1741 doesn’t do?

When we install 100 mA time delayed RCDs there may be a performance requirement stated in BS7671 for a 200 mA fault current, but we do not test it at 200 mA, we test it at 100 mA then make the assumption that if the RCD is performing to specification at the lower current it will perform at the higher.


So with RCD devices how many parameters do we need to test? 


Surely one test test should be sufficient bearing in mind there can be 10 milliseconds difference in the test time result for some RCD devices depending on where it hits the cycle.


Having an anorak moment last night I watched Big C dismantle a Hager RCD on YouTube, the test button whacks it will over 70 mA; and the company have told us to increase the test currents on our testers, precisely testing every parameter seems a bit old school now.


Is it actually needed?


Andy Betteridge

This is effectively the question I am asking Andy but directed at the RDC-DD. Graham has already given his view and given his expertise in this area, I have to conclude that no tests are required. However, it is clear that that Megger, Metrel etc are facilitating such tests on their instrument portfolios. I just wondered where they took their lead from. Perhaps it is nothing more than the manufacturer developing a solution to a problem that didn’t ask for one. Did the demand originally come from the EVSE production line test requirements and this is just a carry through to in-service testing? Whatever it is, I feel almost obliged to equip our training centre with these products even though nothing on the  City and Guilds 2919 EV course would require that! Of course, if I do that, the candidates will assume that this test equipment is imperative for their own work thereby perpetuating a myth that these tests are vital.

Graham has already given his view and given his expertise in this area, I have to conclude that no tests are required. However, it is clear that that Megger, Metrel etc are facilitating such tests on their instrument portfolios. I just wondered where they took their lead from.

Presumably the manufacturers are hoping that a future edition of the regs will make such tests a requirement (shades of AFDDs?)

   - Andy,

Next April we could be installing combined RCBO AFDD devices.


If we do I suspect the number of circuits will be slashed significantly, people are installing a ridiculous number of circuits in some installations protected by cheap as chips MCBs at the moment, that could be about to change significantly. If the new devices are still around £150 each in many installations we will be back to three circuits for lighting, sockets and cooker.


Just assume though that there will be ten circuits with RCBO AFDD devices, under the current regime the RCD function is tested six times, five times with the tester and once with your finger on the test button. Of those six tests, three are actually recorded on the certificate.


So with ten circuits with RCBO AFDD devices we will do sixty RCD tests and record thirty of them, for the AFDD function we will tick to say the test button works, however we will just make the assumption that the MCB function works without testing or recording anything. In reality many of the RCBO AFDD devices only have one test button, so ticking the box to say it works for both the RCD and AFDD function seems to be another assumption.


It appears that some protective device manufacturers say pressing the test button is sufficient and using a tester is unnecessary, yet the tester manufacturers are adding more testing capabilities to the testers.


Electricians are left as piggy in the middle being urged by tester manufacturers to upgrade their testers and do more work that the device manufacturers say is not required.

Wylex Mythbusters


How do I test an AFDD?

Wylex AFDDs carry out a self-test function when initially powered up, and the AFDD repeats this self-test function regularly. They also have a test button (just like an RCD or RCBO), which you can use during the initial verification or EICR. Model certificates now include AFDDs among the devices listed, with space for test results.


So how do we know if the button confirmed the operation of the AFDD and the RCD functions?


If it only confirms the operation of the AFDD function then testing the RCD function with a tester should be carried out every six months.


Andy Betteridge

The original Wylex and Crabtree AFDD were two modules being the AFDD strapped to a RCBO, do had two test buttons, one on each.