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

[kai]

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

I am wondering is it scaremongering by manufacturers, by stating that their RCBO's must be disconnected from the circuit before testing with a megger at 500V?

Has anyone actually ruined an RCBO by meggering it accidentally?.

 

[EFLImpudence]

No. I have a Fluke.

 

[AndyPRK]

You are a lucky boy

 

[flameport]

Not an RCBO, however an RCD FCU ceased working after 500V applied to it.
It was switched on already, power disconnected from the circuit it was attached to so the outgoing side could have some alterations, 500V applied to the outgoing side, when power restored it did not latch on so had to be replaced.
Whether the 500V caused it to be ruined or whether it was already faulty and just disconnecting power from it revealed the problem is unknown.

In another unrelated location, an insulation test was done on a lighting circuit which had 2 Aico smoke alarms attached. The 1000V setting was used. The alarms still worked afterwards.

In reality I would expect any mains powered device to easily withstand 500V, since transients/interference can easily exceed that, and considering that 240V AC is 340V peak, so 500V is not even close to being 2x normal.

 

[Spark123]

Was it a powerbreaker brand FCU by any chance? I have damaged a powerbreaker socket with IR testing before, it would reset but nuisance tripped all the time.
I have also heard of their FCUs going bang big time.

 

[JohnW2]

Has anyone actually ruined an RCBO by meggering it accidentally?.

Not an RCBO, and not 'meggering' (as with EFLI, I 'Fluked' it) - but, as I think I reported here at the time, I did once kill a (IIRC, Wylex) RCD which I did not know existed (hidden in a cupboard) by subjecting it to IR testing it at 500V.

Kind Regards, John

 

[securespark]

I have also heard of their FCUs going bang big time.

Me too. I was near one went it went bang - damn near sh@t mesen. Mind you, not as bad as an old Square D RCBO that I pushed the test button of: there was a massive explosion that blew the board to bits....

Think RF has also had issues with Powerbreaker FCU's going bang.

 

[Spark123]

The new shape Square D RCBOs have been known to char fingers, I don't know if that extends across the merlin gerin and schnieder branded ones too.

 

[Echo the husky]

No RCBOs, but I did take out a power breaker RCD socket the other day.

 

[stillp]

No RCBOs, but I did take out a power breaker RCD socket the other day.

I hope you'll be very happy together.

 

[Echo the husky]

Na, she keeps going off when I try to turn her on.

 

[kai]

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).

 

[JohnW2]

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).

As you say, that's the advantage of active RCDs, but that 'NVR' functionality has nor really got anything (functionally) to do with it being an RCD. The downsides are really simply the corollary of the upsides - that loss of power (even a second or two 'power outage', such is pretty common in my neck of the woods) will leave any connected equipment non-functioning until the RCD is manually reset. Whether the upsides outweigh the downsides, or vice versa, really depends upon the nature and location of the connected equipment/load.

Kind Regards, John

 

[eveares]

Has anyone actually ruined an RCBO by meggering it accidentally?.

I don't know, but if anyone ever has then I guess it would be from downstream of the main DB as not sure why you would want to do a 500v IR test on the RCBO it's self from the non protected side fed by the bus bar. Now I think you can guess that performing a IR test, especially at =>500v on anything with electronic circuitry inside including RCBO's/RCD's is not a good idea.

I am wondering is it scaremongering by manufacturers, by stating that their RCBO's must be disconnected from the circuit before testing with a megger at 500V?

Also, don't RCBO's often have a flying functional earth leads that are used so the RCBO can still operate in the event of a broken/lost neutral. Maybe the manufactures are worried about this may be a unforeseen path for the current to go through during a IR test should the test be done incorrectly?

Mind you, not as bad as an old Square D RCBO that I pushed the test button of: there was a massive explosion that blew the board to bits....

Care to elaborate, surely pushing a test button under normal conditions should just cause the device to operate and open the circuit as expected!? I can hardly see how a IR tester could supply enough current to blow the distribution board to smithereens.

, power disconnected from the circuit it was attached to so the outgoing side could have some alterations, 500V applied to the outgoing side

I take it you were not aware of this RCD FCU that fed whatever you were working on?

 

[JohnW2]

Mind you, not as bad as an old Square D RCBO that I pushed the test button of: there was a massive explosion that blew the board to bits....

Care to elaborate, surely pushing a test button under normal conditions should just cause the device to operate and open the circuit as expected!? ...

... 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"!)!

Kind Regards, John