RCBO's - has anyone actually damaged one by Meggering it at 500V ?

[Spark123]

I always thought that the RCD sockets that trip on loss of power have a big advantage, they disconnect from the mains automatically the moment you either flick the breaker off, or shut off the main switch on the CU. (Of course they were intended for safer use with machine tools, where they needed manual resetting after power loss to prevent accidental restarting).

I'm not sure what brand you use but some of the one's I have come across don't disconnect the circuitry from the supply when tripped. The newer type Power Breaker sockets buzz when pressing the green test button even after they are tripped off.
I had to swop out an MK srcd a few weeks back as it decided to emit a loud buzzing noise when it was tripped.

 

[eveares]

... unless, that is, and presumably due to a manufacturing defect, the mechanism slices through the L conductor when it operates ... see this thread (particularly the photos on pages 2 and 3) which shows and explains what happened when my daughter pressed the test button on her RCD and got a big fright (and she's unfortunately still saying "never again"!)!

WOW!, your daughter's lucky, another good reason to test RCD's/RCBO's when your away from the board. Kind of ironic that a safety device becomes massively unsafe!

Protek!? branded RCD, never heard of them; wonder if it was a MK or some other well known brand whether the same would have happened?

I have a spare unused 80A 30ma Contactum branded RCD in my shed along with a 1000v IR tester, although can't see anything will happen at 1000v DC 2ma though other than possibly damage any circuitry what is inside the RCD.

 

[Iggifer]

WOW!, your daughter's lucky, another good reason to test RCD's/RCBO's when your away from the board. Kind of ironic that a safety device becomes massively unsafe!

Protek!? branded RCD, never heard of them; wonder if it was a MK or some other well known brand whether the same would have happened?

I have a spare unused 80A 30ma Contactum branded RCD in my shed along with a 1000v IR tester, although can't see anything will happen at 1000v DC 2ma though other than possibly damage any circuitry what is inside the RCD.

Protek are a 'known brand' they're not great, but nor are MK's CPDs IMO. And, as has already been said, it happened with a Square D on the previous page of the thread, I'd fit square D over MK any day of the week.

You're welcome to try meggering it and see what happens!

And you could say the same thing about re-energising an MCB that has a fault on the circuit, that could well blow up on you all the same (probably with a bigger bang).

 

[JohnW2]

WOW!, your daughter's lucky, another good reason to test RCD's/RCBO's when your away from the board.

... yes, but we encourage householders to regularly test by pressing the button!

Protek!? branded RCD, never heard of them; wonder if it was a MK or some other well known brand whether the same would have happened?

As has been said, it is a 'known', but not particularly wonderful, brand. However, as I said, it was presumably due to a manufacturing fault, which would probably not have been picked up by in-production testing, so could probably have happened with even the 'best' of brands. That device had been in-service for a number of years, and tested (by pressing the button!) regularly (at least once every 2-3 months) without there having previously been any problem.

I have a spare unused 80A 30ma Contactum branded RCD in my shed along with a 1000v IR tester, although can't see anything will happen at 1000v DC 2ma though other than possibly damage any circuitry what is inside the RCD.

I think that virtually all 'consumer' RCDs now contain electronics, and that's quite likely to be very displeased with 1000V, regardless of current. 2mA is not going to produce a significant bang, but could well kill the electronics.

In my daughter's case, of course, we were not talking of 2mA - but, rather, enough current to immediately blow an 80A cutout fuse! ... hence the very loud bang, smoke, soot etc.! IIRC, the loop impedance at the CU is around 0.25Ω (it's TN-C-S), so the fault current could have been a good few hundred amps.

Kind Regards, John

 

[Echo the husky]

The CGD RCDs only contain a test resistor. I've not opened one of their RCBOs. More householders should be encouraged to test their RCDs, as I'm coming across more and more that fail to trip when the test button is pushed, or an RCD test is carried out. Most just make a buzzing sound as the mechanism has seized as it has been in the same position for so long.

 

[JohnW2]

The CGD RCDs only contain a test resistor.

No electronic trip system? That's interesting, and not something I've seen in consumer RCDs for decades.

More householders should be encouraged to test their RCDs, as I'm coming across more and more that fail to trip when the test button is pushed, or an RCD test is carried out. Most just make a buzzing sound as the mechanism has seized as it has been in the same position for so long.

Ideally, yes - but, as I said, my daughter is now (I suppose 'understandably') very much in a "never again" mode - even though it was a (presumably incredibly rare) 'fluke' that she experienced!

Kind Regards, John

 

[Echo the husky]

No electronic trip system? That's interesting, and not something I've seen in consumer RCDs for decades.

No, the sense coil directly fed the solenoid which releases a tiny catch. I opened a different manufacturers RCD (I forget which one) and there was a little PCB with all sorts of small components on it.

Edit: There was probably a little SMD bridge rectifier between the 2 coils. I will have to check.

 

[eveares]

... yes, but we encourage householders to regularly test by pressing the button!

That's like testing a smoke alarm by pushing it's button rather than using smoke spray, RCD's need to be periodically tested to ensure they trip within the required time and current limits for 1x and 5x of their trip current. Thus the importance of people having their RCD's & RCBO's tested by competent people.

 

[JohnW2]

That's like testing a smoke alarm by pushing it's button rather than using smoke spray...

It is, but pushing its test button is obviously better than nothing, and certainly can be done far more frequently than one could possibly expect people to have them tested 'properly'. Furthermore, regular testing will actually have some 'therapeutic' benefit, since it will help to prevent development of the 'stiction' which often occurs when an RCD has not operated for years.

... RCD's need to be periodically tested to ensure they trip within the required time and current limits for 1x and 5x of their trip current. Thus the importance of people having their RCD's & RCBO's tested by competent people.

That's the ideal, but the practical reality is that it's usually just not going to happen - at least, not more frequently than 'once every several years'.

KInd Regards, John

 

[Echo the husky]

Not quite testing RCDs but testing switchfuses, this brand new one must have had something conductive rattling around in it. When I pulled out the plug from the socket beside this, something went bang but I couldn't see what. Reset the RCBO and switched on the switch fuse, and it went with a big bang, and sparks shot out around the switch.

The fault was L-N after the switch but before the fuse. Must have been intermittant as it passed a 500V insulation resistance test minutes earlier. It would have been much more spectacular if the 3036 fuses were still in place! I opened it up and it was jet black inside.

The clean part of the switch was where my finger was!

 

[eveares]

The fault was L-N after the switch but before the fuse.

Now shouldn't the fuse be before the switch in the FCU? Was it single pole or a double pole switch also?

 

[Echo the husky]

Double pole, most I have seen have the fuse after the switch so you are not digging around a live fuse when trying to remove it.

 

[JohnW2]

Double pole, most I have seen have the fuse after the switch so you are not digging around a live fuse when trying to remove it.

I think it's many years since I saw one which did not have a DP switch, and I'm not sure that I've ever seen one in which the fuse came before the switch - for the reason you mention, it wouldn't really make sense.

Kind Regards, John

 

[eveares]

Double pole, most I have seen have the fuse after the switch so you are not digging around a live fuse when trying to remove it.

Don't you normally have to pull the fuse holder out thus disconnecting and isolating the fuse from the mains before removing. And how about removing a fuse from a un-switched fused spurs without turning off the load, or unplugging a high powered item without switching it of first?

 

[EFLImpudence]

Don't you normally have to pull the fuse holder out thus disconnecting and isolating the fuse from the mains before removing.

Yes.