CU change and inspection

Discussion in 'Electricians' Talk' started by Monty125, Jul 31, 2020.

  1. Monty125

    Monty125 New Member

    I’ve had a quote for changing a domestic consumer unit, this will also include a test certificate. What would normally be tested when replacing (or what is required to be tested)?
  2. nigel willson

    nigel willson Screwfix Select

    Existing wiring needs testing so that any faults can be rectified before the unit is changed . Rcd board cannot be energised with existing faults
  3. Monty125

    Monty125 New Member

    Does that include testing plug and light sockets ect?
  4. MGW

    MGW Screwfix Select

    Much depends on the electrician, the problem is once you start fitting a CU with RCD protection there is not much you can do if you find a fault. With the so called high integrity board you can put a few circuits on their own RCBO and with an all RCBO board you could simply leave faulty circuits dead, but you would not be very well thought of, so most electricians want to tell the client what faults exist before they start.

    However they are not doing an electrical installation condition report (EICR was called PIR) and as long as the RCD will hold in and no obvious faults, then they don't really go too deep, ensure a ring is a ring, and the insulation reading is OK.
  5. Bogle Crag

    Bogle Crag Active Member

    Not forgetting polarity
  6. Alwaysworking

    Alwaysworking Active Member

    Just out of interest, isn’t getting polarity correct an absolutely basic thing, or am I missing something?
  7. Bazza

    Bazza Screwfix Select

    A full electrical installation certificate will need to be completed following the change of a consumer unit. This will test the characteristics of each circuit to confirm they meet the required standard.
    The installer will not check every point on every circuit. Investigation will be needed if any fault is discovered through testing. These faults can be expected to be an additional cost.

    A wise electrician will make basic checks before disconnecting the old board!

    Note: as well as certification, the change of CU will need to be notified to the LABC. Make sure that your electrician is going to do this!
  8. MGW

    MGW Screwfix Select

    Due to the notifying of LABC I did not DIY my CU change, however it was left to me to find the fault on the lights with a borrowed neutral and correct. I did not mind doing this, it is what I expected to do, however clearly the electrician did not do all the checks as he missed it. In the ideal world yes maybe he should test all circuits, but in the real world there are good and bad.
  9. spinlondon

    spinlondon Screwfix Select

    Why are so many of you saying existing circuits should be tested?
    Have any of you actually read BS7671?
  10. Bazza

    Bazza Screwfix Select

    Yes. A change of CU requires a full EIC. The schedule of test results (there’s a typical one in BS7671) has lots of boxes in which you put numbers in for all sorts of measurements for each circuit. remember that?

    This sort of thing
    Last edited: Jul 31, 2020
  11. Monty125

    Monty125 New Member

    I was presuming that an EICR would be required for a CU change

    One quote was cost of CU replacement plus £20 per circuit for the inspection if I wanted an inspection, which made it quite expensive.

    all the other quotes include inspection, but did not state the extent of the inspection
  12. spinlondon

    spinlondon Screwfix Select

    A CU change requires an EIC (not sure what an un-full EIC would be).
    You are required to conduct appropriate tests (just imagine what tests you would conduct if there were no out-going circuits).
    This is from the guidance for recipients on the back of the EIC form:
    “This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration to an existing installation. It should not have been issued for the inspection and testing of an existing electrical installation. An 'Electrical Installation Condition Report' should be issued for such an inspection.”

    Now if anyone can find something in the Regulations where it states a full EIC (whatever that is) should be issued, or anything that states the existing installation should be tested when making an addition or alteration. Please do so (I can save you some time, don’t bother because there’s nothing there).

    What would be appropriate to test, would be continuity of the Earth conductor (Ze).
    Prospective Fault Current.
    The operation and effectiveness of any RCDs installed as part of the work.
    And perhaps the continuity of any bonding conductors?

    I hear arguments sometimes, about changing the characteristics of a circuit, that by doing so, you would effectively installing a new circuit.
    Of course such arguments are rubbish and there’s nothing in the Regulations to support such an argument.
    Some people argue that the Zs of a circuit might not be low enough to operate the new protective device.
    That’s a good point, but surely in order to comply with the Regulations, you should have checked that before making the addition or alteration?

    If you’re changing from re-wireable fuses to MCBs or RCBOs, you will have to check the Zs on any existing circuits of 10A and less, because the maximum Zs for re-wireable fuses is higher than is allowed for MCBs and RCBOs.
    Anything above 10A, then the maximum Zs for re-wireable fuses Is lower than is allowed for MCBs or RCBOs.

    So to conclude, test before you change the CU, not after.
    On the EIC, only record details of circuits which could possibly affect the safety of the CU.
    Do not test existing circuits, as they are not part of the extent of the work covered by the EIC.
    Sparkielev likes this.
  13. Sparkielev

    Sparkielev Screwfix Select

    Whenever I do a board change I do basic tests before I start, check bonding if I see any issues then I inform the customer if they refuse to do any issues that is going to cause problems by fitting the new unit then it is pointless fitting the board, most agree
    MGW likes this.
  14. MGW

    MGW Screwfix Select

    I agree with @Sparkielev once the board is fitted it is a little late to say by the way your lights will not work until some one finds the borrowed neutral and corrects it. So some tests are required. However with an EICR we expect a reasonable number of sockets and switches to be removed and inspected, but all you need with a board change it to test items altered. So a fuse to BS 3036 to a curve B MCB yes OK need to measure the loop impedance, but replace one curve B with another curve B then simple insulation resistance is all that is required.

    So fitting a RCD either with a lower tripping current or when there was not one there before, should really put the clamp-on ammeter on the pair of live cables and measure the leakage, we know with a 30 mA RCD the limit is 9 mA, if over 9 mA the circuits need splitting until under 9 mA, OK we all know we should, hands up all those who do.

    All I have done is check the insulation resistance, which is a DC measurement so useless. I will hold up my hand and say no I never checked, why, well that's simple my clamp-on ammeter would not measure 9 mA. In non of the places I have worked have I ever had access to a clamp-on that will measure 9 mA.

    Yes loop impedance/prospective short circuit current, yes 500 volt DC insulation tester, yes RCD tester, but no clamp-on able to measure 9 mA. And when I took my C&G 2391 no one said I should. But since 2008 it has said I should divide the installation so as to
    "reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation"
    The only way I know if I have divided it into enough circuits is to measure the earth leakage, and the only test gear I have which would measure that is my PAT tester.

    So what I have done is use all RCBO consumer units, and no problems.

    What we hope is we don't get caught, and if we can't write down on a test certificate earth leakage 4 mA with no items in use, then do you want to fill out any form? I have seen people print out their own forms, if you don't have a meter to give you the ELI then design a form that does not ask for it.

    So we all know 106 meters of 2.5 mm sq is allowed with a final ring, so the Ze is 0.31 Ω hands up how many measure the centre of the ring and work out if the permitted volt drop is exceeded, OK I know I want less than 0.90 Ω line - neutral so volt drop is within 11.5 volt, however I also know most people don't bother measuring it, and use a schedule of results form where it is simply missed off the form.

    Today we know the dangers involved when any AC is rectified to DC and it is not full wave, be it due to a faulty diode or design, we know in real terms type A or better RCD's should be fitted to anything likely to have rectifiers in it, yet my local supplier does not even hold type A in stock, he only has type AC.

    So we all know we in the main are not doing the job right, we have cut corners as far back as I can remember, I personally think some one who admits he does not do a full EICR is better than some one who says he does one, but misses anything he does not fancy doing out.

    I have been reading on another forum how SSE do an insurance and as part of it do an inspection, it cost £63.60 for insurance and the poster was convinced his house was A1 as the inspector had never picked up on any faults, this was a TT installation and a 100 mA RCD and old Wylex board where the fuses had been replaced with MCB's, he wanted to fit a larger shower and could not see there was anything wrong with his insulation. If there was then the SSE inspector would have highlighted it.

    Let him without sin throw the first stone.
  15. timotay

    timotay Active Member

    It is unbelievable to me that anyone could consider installing a new DB and not complete all the prescribed testing to ensure that they are leaving the installation safe.
    Exactly which tests could be omitted which would not be considered as needed ?
    Bazza likes this.
  16. sparko69

    sparko69 Active Member

    ' So to conclude, test before you change the CU, not after.
    On the EIC, only record details of circuits which could possibly affect the safety of the CU.
    Do not test existing circuits, as they are not part of the extent of the work covered by the EIC'

    Seems to contradict himself with that statement as any installed circuit could affect the safety of the CU.
    I'm baffled by the claim that you do not need to test existing circuits and I've never heard that before.
    Sounds like someone is planning a drive by consumer unit change to match a drive by EICR
  17. unphased

    unphased Screwfix Select

    Its an interesting topic this. Until now I hadn't given it much thought, I'd naturally assumed that you tested all circuits when changing the CU and included these as part of the EIC. However, I now accept spinlondons view that the circuits CANNOT be certified because they were all installed by someone else. You can only check them and provide an EICR for the circuits. The circuits themselves should have been certified by the original installer, but the joke is the test certificate is mysteriously never to hand. The CU itself is new, so IT must be certified with an EIC because it is a change of electrical equipment. The tests applicable to the CU would be the Ze, PFC, PSCC, 30mA RCD tripping times and test button press. You are confirming polarity by doing the Ze and continuity of the main earth conductor. The main bonding conductors are supposed to be checked for continuity, too.
  18. Bazza

    Bazza Screwfix Select

    But must do other tests too. For example.
    Let’s assume you have what appears to be a ring final. I mean it obviously must be a ring because it has two conductors going in to the 30amp fuse on the old Wylex board!
    Not obviously at all.

    If you don’t even check the continuity of the ring you could be installing a 32A MCB on a broken ring.
  19. timotay

    timotay Active Member

    I would further state that anyone worth their salt....would be a total cowboy and legally liable
    ......if they did not confirm by Inspection and Test that the installation was "Safe" after a major electrical modification... and before energising.
  20. Coloumb

    Coloumb Screwfix Select

    Seems daft to suggest changing the CU would only require an EICR. What about the CU, that would need an EIC then a separate EICR for the circuits? Pointless.

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