Who trusts RCDs?

[Piratepete]

Hi Guys
Did a small job in a house - one additional socket. Then did an RCD test - x1 (240 mSec) and x5 failed miserably. did the test a couple more times. Some improvement but still failed. The RCD is an old Wylex WSES 80/2 so replacement means a new CU. Customer asked me to test it again - it passed and continued to do so! Stabilised at 106/10 mS. Asked him when he last pressed the Test button - 6 years ago!

I assume that it just got sticky from lack of use! Does this happen to modern RCDs? I must admit that though this is the first that I've tested which failed about 5 operations I've tested many which initially give high readings (though not failed) first time around.
It seems a bit crap if whether you die or not all depends on whether the householder has pressed the test button in the last 6 months!:icon13:
Pete

 

[fivestar]

I have found quite a few new ones faulty, not just the old ones

 

[Engineer54]

At school we were taught to do the x.5, x1 and x 5 tests before the functional (red button) test as the object is not to try and get the thing to work for the purposes of testing but to test it's operation as it is, the thinking being if it misbehaves once, what is to stop it misbehaving again after you have left. We were told in no uncertain times that a first time fail is a fail, no argument, and the unit should be replaced

Seems these lecturers make up there own rules and standards, and have little or no time for manufacturers instructions/recommendations!! I wonder why on just about every MFT/RCD tester, the ''Auto'' sequence is 1/2 / X1 / X5 on both 0 and 180 degree's?? Perhaps the manufacturers don't know what they are doing...

As for a first fail and it's a dud, makes you wonder if they have ever been in the field?? Perhaps they have, and didn't last too long with any of their employers, and why they are teaching now. Trouble is, they are now teaching all the nonsense, prejudices and scaremongery that caused them to fail in the real world!! ...lol!!!

 

[GLENNSPARK]

Fair point, but from my experience the second trip and subsequent re often better than the first, so rather than condemn what could be the whole board for a first trip failure, i test it to MY satisfaction

if an RCD fails any tests its subjected to first time round (including the manual test)...it should be condemned...

 

[Engineer54]

if an RCD fails any tests its subjected to first time round (including the manual test)...it should be condemned...

Wouldn't agree with that statement at all!! In a perfect world maybe, where they have been regually tested by the house owner or whoever!! But they are all too often not checked at all from the day they were installed and the mechanical side of these units could well stick until operated a few times... and perfectly fine thereafter!!

 

[plugsandsparks]

Guys its nice to have these sentiments but look at it from another point of view.

RCDs dont get tested every 3 months - do they ? - NO

When they trip for the first time having never been surprised perhaps in their life before, they can be a little slow off the mark. Its OK as i am a little slow in the morning as well. BUT i do get better as the day goes along and you know there's nothing wrong with me (i think). So you are faced with obsolete breakers and a new board circa £300 but hey although it was slow on X1 0 it actually passed X1 180 and X5s. So you try the test button, wow its electric now and you run another test, it passes, you have a coffee and try again and compare results... now we are cooking. I pass it ..

My example was a little extreme with 3 RCBOs failing and quite frankly i did not like the look of the DB but thats a difficult sell to the client "Hey P&S does not like the look of our stuff" So i gave the DB ample opporunity to re-deam itself and when the smell of the fried RCBO wofted into the air, i had no problem convincing the client its a bad board and must go, much better than saying "hey guys these rcds have failed first trip, so the whole lot has to go"
They say "have you tested it again?"
I say "yes its fine now but my school says i must condemn it at the first attempt"
They say"should have gone to a differnent school"
I say " steady on i'm sensitive you know"

 

[mhar]

Of course the other way of looking at it is that you know that this particular rcd is prone to being a bit sticky and you are therefore leaving a protective device in situ that you can be pretty certain that, after a period of time, will not perform to bs or en standards.
In defense of the teachers at school they are obliged to teach best practice. I have no criticism of their teaching.
I am not criticising anybody, merely passing on what I have been taught and the reason why I was taught that

 

[plugsandsparks]

Thats OK, not saying its best practice but they are not tested every 3 months as recommeded, in reality so if i use your teachings i should be replacing most RCDs i come across when all they really need is a little practice and then we are back to following the manufacturers recommedations after i have left, hence i do go through alot of RCD labels, do i think it makes a difference? dont know, but i have done my best. Whose to say replacing it will last any longer than 3 months, certainly the manufacturers will baulk at replacing them under warranty if they are not.

Dunno - you use your best judgement in these situations, i can usually tell whether i am going to have a problem as soon as i look at the board.
e.g. New schneider RCBOs are work of art, they are almost identical in readings often to the msec, pretty impressive, well i think so.
If the DB has a door and i find it shut and clean inside i have high expectations, if the door is missing and or, there is a 5mm pile of dust sat on top of the breakers - low expectations, signs of corrosion from a leaky roof, its getting worse now.
End of the day i would not pass something i was not happy with nobody should

 

[Richard]

It's always got me that theres no test as such for proving MCB's...I'v replaced plenty of faulty Rcd's because its easy to prove that their defective, but how do you actually know that an MCB will trip when is should? after all, it is just a mechanical device, which I assume could at somepoint develop a defect.

 

[plugsandsparks]

It's always got me that theres no test as such for proving MCB's...I'v replaced plenty of faulty Rcd's because its easy to prove that their defective, but how do you actually know that an MCB will trip when is should? after all, it is just a mechanical device, which I assume could at somepoint develop a defect.

Yep, has bugged me for ever, only ones i have changed have been because they are tripping too early, not too late or never.

Fusewire suddenly looks appealing again

 

[Engineer54]

It's always got me that theres no test as such for proving MCB's...I'v replaced plenty of faulty Rcd's because its easy to prove that their defective, but how do you actually know that an MCB will trip when is should? after all, it is just a mechanical device, which I assume could at somepoint develop a defect.

Actually, there IS, but are generally far outside the general journeyman electricians reach as far as the cost of these test units... With the same type of test equipment, you can also test MCCB's ...

Generally MCB's are a proven technology and are far more reliable than any manufacturers RCD devices. We only test MCB's when they are suspected of being faulty...

 

[IQ Electrical]

It's always got me that theres no test as such for proving MCB's...I'v replaced plenty of faulty Rcd's because its easy to prove that their defective, but how do you actually know that an MCB will trip when is should? after all, it is just a mechanical device, which I assume could at somepoint develop a defect.

That's always my point when RCD MTBF is being discussed, also, imagine the amount of faults that are many times the I delta n value of the device, you'll normally find that the 'failed' device will still open at these values.
ERA did a good report with some extensive research on RCD failure and the final pass rate was found to be above 97%.

 

[Engineer54]

ERA did a good report with some extensive research on RCD failure and the final pass rate was found to be above 97%.

All sounds quite impressive, ....until you read a little deeper into this report, and find that the total number of units involved in making these assumptions are so small it becomes meaningless, that's apart from where these units were drawn from!!! You then have to start asking, ...Who actually paid for work on this report, and who is this report favoring??

Now look at these forums here, and the amount of RCD (of all types) problems encountered by the members here. No not all of them are faulty, but the vast majority are!! Not a day passes where you don't see RCD in the thread titles!!

The last project i was involved with, had literary thousands of all kinds of RCD devices,(As will my present project) and all top brand units. The contractor was sending a box or boxes of the things back to the manufacturer on almost a monthly basis for replacement, all after confirmation bench testing...

You can take that ERA 97% pass rate with a very large pinch of salt and with a few tongues in cheeks too!!!

 

[IQ Electrical]

All sounds quite impressive, ....until you read a little deeper into this report, and find that the total number of units involved in making these assumptions are so small it becomes meaningless, that's apart from where these units were drawn from!!! You then have to start asking, ...Who actually paid for work on this report, and who is this report favoring??

Now look at these forums here, and the amount of RCD (of all types) problems encountered by the members here. No not all of them are faulty, but the vast majority are!! Not a day passes where you don't see RCD in the thread titles!!

The last project i was involved with, had literary thousands of all kinds of RCD devices,(As will my present project) and all top brand units. The contractor was sending a box or boxes of the things back to the manufacturer on almost a monthly basis for replacement, all after confirmation bench testing...

You can take that ERA 97% pass rate with a very large pinch of salt and with a few tongues in cheeks too!!!

The Electrical Safety Council commissioned and paid for the report, it was done across 607 installations, it's all we have at the moment.
RCDs are still type tested to BS61008/BS61009 exactly as an MCB/MCCB is tested to the applicable standard, the obvious difference being that the RCD is abundantly easier to test when in-service as per the requirements of BS7671.

 

[SPARTYKUS]

I changed two volex MCBs last week that were intermittently coming back on.

Dodgy.

 

[Engineer54]

]The Electrical Safety Council commissioned and paid for the report,[/B] it was done across 607 installations, it's all we have at the moment.
RCDs are still type tested to BS61008/BS61009 exactly as an MCB/MCCB is tested to the applicable standard, the obvious difference being that the RCD is abundantly easier to test when in-service as per the requirements of BS7671.

Look a little deeper on how the ESC/ERA operates and who finances them....

So what are you saying, ...that this ERA report ultimately proves that RCD's are as reliable as MCB's/MCCB's??