RCD Test button wont trip

[JohnW2]

Nobody tests MCBs, either.

I forgot to add that I'm a little surprised you didn't suggest a 'homebrew' test for this, as well, since it again only requires Ohm's Law (and maybe some wire resistance tables and some PPE) - a B32 should trip 'almost instantaneously' at 160A.

Kind Regards, John

 

[Monkeh]

Nobody tests MCBs, either.

I forgot to add that I'm a little surprised you didn't suggest a 'homebrew' test for this, as well, since it again only requires Ohm's Law (and maybe some wire resistance tables and some PPE) - a B32 should trip 'almost instantaneously' at 160A.

Kind Regards, John

That's slightly more dangerous. And I don't like making lights flicker, it's rude.

 

[JohnW2]

That's slightly more dangerous. And I don't like making lights flicker, it's rude.

Fair enough! I suppose you could turn the lights off while you were doing the test, so that they didn't flicker

Kind Regards, John

 

[Click4]

or for the extreme DIYer... just make a direct short between the MCB and earth.

(not to be tried... I am not recommending it, its highly dangerous and im only joking)

 

[JohnW2]

or for the extreme DIYer... just make a direct short between the MCB and earth. (not to be tried... I am not recommending it, its highly dangerous and im only joking)

(still joking) ... that would be non-quantitative and therefore non-scientific - the 'direct short' needs to be of known resistance (hence my reference to wire resistance tables) - but you'd have to guess at the Ze to add on

Seriously, though, given our high level of dependence on MCBs, it's a major (but seemingly unavoidable) flaw of the system that we can't test them. As RCDs come to cover more and more circuits, there is very often that 'backup' in terms of L-E faults, but there's no backup for L-N faults other than the cutout fuse - and the wiring of many a final circuit (particularly lighting ones) might well become ill (if not melt) before the fuse even started thinking about operating if there were a non-zero-impedance L-N fault (say 80-100A fault current), or even a serious overload, that was not cleared by a faulty MCB.

Kind Regards, John

 

[Click4]

Yep it is a flaw, even more important they are working when DIYers have sometimes been at them.

On that consumer unit I posted a picture of.

Some idiot, they had removed 1 bedroom from the upstairs socket ring, and put it on a circuit on its own.. That 1 Bedroom circuit was wired into the mcb labelled sockets.

But the rest of the upstairs was wired into a 40amp mcb labelled shower!
Not just that RCD was not working either, reset button didnt trip it, didnt respond to test.. And also when resetting it have to say it felt really notchy... Was even making funny clicking sounds as you reset it (when moving the switch upward)

So if it was Bad enough it had a 40amp mcb protecting the sockets... Which were wired in 2.5mm but worse still if that mcb was faulty... A fire waiting to happen.

Which shows as you say the importance of testing them, but yet is something that can't easily presently be tested.

 

[ricicle]

So, do you test plug-in RCDs to make sure they're not half a ball hair outside the published tripping times?

Nobody tests MCBs, either.

And no, I'm not looking for a long, drawn-out discussion from the armchair brigade on either subject.

No homeowner (without test kit) would test a plug-in RCD. But as an electrician charging for your services supplying one to the customer, I would hope you would test it. It's the same for the RCD in the original post - the OP thinks that as he owns the property he is immune from the dangers of electricity. Even worse if he is a landlord and is going to charge rent for the place !

 

[themoosdad]

It's the same for the RCD in the original post - the OP thinks that as he owns the property he is immune from the dangers of electricity.


Funny, but i dont remember saying that!

No one is immune from the dangers of electricty, including yourself.

Just because someone doesent have a qualification in something, that doesnt mean they are not capable of understanding and comprehending. There are plenty of so called qualified electricians that dont know their arse from their elbow, as there are in all trades.

Common sense plays a huge part in the safety of so many things.

I saw some electrical work (including a new CU) in a property that is leased to the council only 3 weeks ago. The work was carried out by an electrical contractor approved by the Local Authority. The quality of the work was disgusting and i dont need to be a qualified/certified person to know/see that!
Maybe i should pay that person a quanitity of money to do the job for me, because as they are an electrician and i am not, it is obvious that they are much more capable!!

Not replying to any more comments on here. Never known a forum like this one!!

 

[ricicle]

It doesn't matter how much you bleat on - if you have installed a consumer unit without testing properly then you have no business doing electrical work. End of.

 

[JohnW2]

Yep it is a flaw, even more important they are working when DIYers have sometimes been at them. ... Which shows as you say the importance of testing them, but yet is something that can't easily presently be tested.

It's rather hard to see that it ever will be routine. After all, the problem is not that we don't know how we could do such a test (it's remarkably simple) - but, rather, that it's difficult to see how ir could be done safely with in-situ MCBs on-site. The inspector, installation and premises would all be at some risk.

As I wrote last night, I do worry a bit about how reliable MCBs actually are, particularly given how cheap they can be. There is this common belief that RCDs are much less 'reliable' (with "1 in 7 faulty when tested" often cited), but I don't really see what evidence we have that in-service MCBs aren't 'as bad. One imagines that the thermal part of operation will virtually always remain operative (even if it doesn't operate at quite the right current), but the magnetic part may well be subject to similar reliability issues to those seen with RCDs.

One of the most important aspects of modern testing is the measurement of EFLI, as a means of 'confirming' that ADS requirements are satisfied (which is clearly a major safety issue) - but a satisfactory Zs measuremnt obviously counts for nought if the magnetic trip of the corresponding MCB does not work like wot is says on the tin!

Kind Regards, John