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RCBO's and IR testing

Jaymack
I have had a problem with 5 off Wylex RCBO's. These were bought by a houseowner and fitted by him as there was no RCD protection for some circuits requiring such. These Wylex RCBO's have a warning hidden on the body that connections should be disconnected for Insulation Testing ..........too late the man cried!. For expediency and availability, I have redesigned the arrangement to have MCB's with a common RCBO as a M.S..

I have been in contact with Wylex technical help, who say that they should have been OK to withstand 250V IR testing as in this case, but to return them to the dealer. Anyone else have had similar problems?


Jaymack .
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    What happened to the RCBOs?


    In a way I'd expect them to survive - after all (looking at table 443.2) they should be able to withstand a 4kV pulse - so 500V should be fine (at least for a short duration). If they failed on a 250V d.c. test I can't imagine how they'd work in service where a 230V r.m.s. waveform peaks at over 325V.


    Sure most need disconnecting (a few sensible designs notwithstanding) - but for reasons of not causing false failures of the test rather than (I'd hope) risking the RCBO itself.


      - Andy.
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    AJJewsbury:

    What happened to the RCBOs?


    In a way I'd expect them to survive - after all (looking at table 443.2) they should be able to withstand a 4kV pulse - so 500V should be fine (at least for a short duration). If they failed on a 250V d.c. test I can't imagine how they'd work in service where a 230V r.m.s. waveform peaks at over 325V.


    Sure most need disconnecting (a few sensible designs notwithstanding) - but for reasons of not causing false failures of the test rather than (I'd hope) risking the RCBO itself.


      - Andy.




     

    I agree with the comments here, the RCBO's have open circuited and had to be replaced, in this case with MCB's and a common old garden Main Switch, (not an RCBO as I stated). If the case that connections require to be removed for testing, then this warning notice should be "In your face" as a sticky. Though what a chore where a quantity of these units are used for redundancy of circuits!. 

    In the meantime, I will arrange for these to be returned to the supplier for analysis by Wylex; I doubt that the supplier will give a refund at this stage however. At this stage, it seems that Joe Public is the final tester and the market is the ultimate test bed. Such is progress .............. a la Boeing. This is a Wylex product, but is the same applicable to other makers?, are the common manufacturing standards at fault? .


    Jaymack.    .
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    Further to my previous post, there is a make of RCBO that only needs to be switched off for IR testing a CU,

    This article is from October 24th 2018. To quote "However, all of that can be avoided with Crabtree Miniature RCBOs, as they are two-pole switching devices. The only thing that has to be done to get a circuit ready for an insulation resistance test is to switch the device off. This saves time and money from your annual budget on essential testing, and provides higher levels of protection for all who interact with it. In a single second the circuit is ready to test. There’s no need to disconnect the circuit cables, no need to attach test leads, and no need to be concerned about reconnecting cables either. All of which makes this testing process easier, faster, safer and cheaper too". see the link


    Jaymack

    https://www.electrium.co.uk/news/rcbo-spells-savings-for-testing
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    You could reasonably argue that anyone who is competant enough to test safely should also have the knowledge of the risk to sensitive devices and appliances otherwise have no business testing. Householder or electrician. A little knowledge can be a bad (dangerous?) thing
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    The miniature Wylex RCBOs are exactly the same as the Crabtree ones. I have never had any issues with the wylex ones.

    Nick
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    I agree with the comments here, the RCBO's have open circuited and had to be replaced,    

     




    I can't understand just why this should have happened. Surely the contacts are just mechanical in operation. I do assume that there is no continuity between the supply side and load side terminals.


    Z.

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    there is not, but the internal electronics is powered from the load side - if it was not, it would be in an effectivly unfused supply.

    However, I too am surprised it cannot stand a short flight to 500VDC, as it is supposed to take mains all day, and surges of a few kV.

    It is a bit of an oversight in the product spec that connection of test gear was not foreseen and put on the list of things to test and must survive.

    Equally I think surviving 400VAC from a lost neutral event should also be there in the list of approved tests, but it seems that too isn't.
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    I increasingly think that subject to a pass at 500 V on initial verification, a good result at 250 V will do for a periodic.


    These devices seem to make a whole-board IR test at 500 V impossible.


    My 17th+3 version of GN3 makes the point that functional earths should be disconnected and has a list of devices as long as your arm which are vulnerable to IR testing. It makes me wonder whether anybody will want to prepare reports for private landlords.


    And BTW, if an SRCD needs to be disconnected (as MK recommend) and two or more are fed from a ring, how do you IR test it? The same may apply to USB sockets.
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    AFDD- Arc Fault Detection Devices are on the list of equipment that cannot be subjected to a 500 volt global insulation tests.


     Andy Betteridge.
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    Which Wylex RCBOs are they?


    The new double pole RCBOs advertised benefits include:


    “Wylex RCBOs go one step further, they have switched neutral built in as standard, live and neutral conductors do not have to be disconnected for insulation resistance testing. This saves time and money, particularly for responsible landlords who regularly test installations during occupancy voids.”

    Electrium

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