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The testing required before cu change

Discuss The testing required before cu change in the Electrical Forum: General Electrical Forum at Tilers Forum; I知 about to change an CU with rewireable fuses to one with RCBOs, the reasoning behind this is, only a small CU will fit the space and the property only ...
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    Default The testing required before cu change

    I知 about to change an CU with rewireable fuses to one with RCBOs, the reasoning behind this is, only a small CU will fit the space and the property only has 4 circuits
    5amp Upstairs Lights
    5amp Downstairs Lights
    30amp Sockets
    30amp Cooker
    If I use MCB all circuits are protected by an RCD, therefore all circuits would be interrupted under fault conditions; an RCBO ensures that only the circuit with the fault is interrupted.
    I plan to test the installation before removing the old CU and because I will be fitting RCBOs I want to avoid any problems with N-E.
    Now I値l get to the point (typically of a woman to go all around the houses)
    Tests are:
    Ze and Psc tests
    Continuity of protective conductors test ( R1 & R2 test at the furthest of the 2xlight circuit and the cooker circuit, adding it to Ze to get Zs). But how does this test check neutral
    Then the end to end testing on the sockets circuit
    Followed by the cross over test, I know the reading at each socket should be (R1+Rn)/4 or (R1+R2)/4 (spurs higher)
    Then Insulation resistance test on all circuit.
    Then Zs test of all circuits
    Is there anything else I should do or lookout for to avoid problems with the RCBOs
    By the way, Which RCBOs are the best to use.
    Feedback Welcome
    Many Thanks

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    Default Re: The testing required before cu change

    The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.

    I often prefer MK RCBO's


    Often when I introduce RCDs to an existing installation I will carry out a continuity test between neutral and cpc, to see if any leakage is already existing.
    Another thing i do is carry around with me a plug in RCD unit, which I will try out on any suspect old appliances prior to installation. It isn't guaranteed to pick out problem appliances (RCDs have different sensitivity) but it does Ilustrate to the clients your concern prior to installation.
  3. Earthing limits duration of touch voltages, bonding limits the value of touch voltages


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    Default Re: The testing required before cu change

    Many Thanks

    [The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.]

    To complete this test, would I link neutral to cpc at CU just like R1&R2, and what reading should I expect?
    Just look up the plug in RCD units, does it indicate if a electrical appliance is faulty.



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    Default Re: The testing required before cu change

    would a split load consumer unit not suit your purpose?
    assuming by post you are new - if so life would be made much easier and cheaper this way.

    dont go overboard on initial testing,
    ze
    ring continuity
    basic ir test
    " There are 10 types of people in this world - those who understand binary, and those who don't "

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    Default Re: The testing required before cu change

    Your readings will all depend on your circuit length and if you have spurs or not.

    Soulnds like another diyer taking work of the good old sparky again

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    Default Re: The testing required before cu change

    Quote Originally Posted by Amp David View Post
    Your readings will all depend on your circuit length and if you have spurs or not.

    Soulnds like another diyer taking work of the good old sparky again

    seems a little well informed for a diyer - im thinking new partp or trainee
    " There are 10 types of people in this world - those who understand binary, and those who don't "

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    Default Re: The testing required before cu change

    Thank you Widdler and Ezzzekiel for the advice
    Looked at split load consumer unit first but can’t find one that would fit the space I’ve got to work with, which is measured at
    W- 250, D - 120mm & H - 260mm
    I am new to the forum, and qualified in June NOT A DIYER TAKING WORK OFF THE GOOD OLD SPARKY AGAIN as Amp David suggested.
    Just look for some advice like anyone else.

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    Default Re: The testing required before cu change

    Feel for the customer

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    Default Re: The testing required before cu change

    Quote Originally Posted by MrsS View Post
    Many Thanks

    [The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.]

    To complete this test, would I link neutral to cpc at CU just like R1&R2, and what reading should I expect?
    Just look up the plug in RCD units, does it indicate if a electrical appliance is faulty.

    The plug in tester should work like a normal RCD and hopefully trip if an individual appliance was giving off sufficient leakage to cause problems upon completion. Suspect appliances can be old fridges, washing machines or PC's etc. This won't account for the quantiy of appliances though, which may when all in operation, build up an amount of leakage sufficient to also trip the RCBO anyway.

    As for the neutral, yes you could connect it to CPC at the board. Assuming that you have T&CPC cabling, you could play around with the data to verify readings for comparison. (R1&Rn)/2= R1 or Rn. Therefore R1&R2 should equal (R1x1.67)+R1. Then you will have the figures for R1, Rn & R2.

    This is all unnecessary though for current requirements, and so I'm sure others here are probably wondering what the heck I'm talking about.
    Earthing limits duration of touch voltages, bonding limits the value of touch voltages


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    Default Re: The testing required before cu change

    amazing really the simple things


    customer can see it for himself -before you changeover to 30mA protection

    and have to explain it


    err you need to order a skip for all your equipment that worked before i started
    Last edited by davelerave; 15-09-2010 at 05:09 PM.

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    Default Re: The testing required before cu change

    Got to get myself a plug in RCD tester, always handy to help sort out faults.
    I’ll give the neutral test ago. Many Thanks

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    Default Re: The testing required before cu change

    Separate all your neutrals and IR test (or you could continuity test) between them - (there are 6 different combinations with 4 circuits) If you get a zero on any of them chances are you have a shared neutral and potential problems with your RCBOs. If you do have this problem then at least with a split board, although not ideal, you have the opportunity to put the offending circuits on the same rcd and save taking up floorboards/chopping out walls etc.
    Of course do the other tests as well to check for other problems. Good luck

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