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  1. ennaress
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    ennaress EF Member

    Location:
    Petersfield
    Did an EICR opened the CU and found this burnt charred Neutral running downstream of the (main switch). What should I be looking for (other than a replacement tail)?
    There were two or three C2 observations that may well have caused an overload - eg 5kW of water immersion wired into the ring final and the oven run off a 13a plug, but the live conductors looked OK.
    Installation over 35 years old.
    OC or very low IRs on all circuits.
    R1+R2 ok as was Zs.
    I know one answer would be a whole re-wire, but I want to know what caused this.
    Thanks for any helpful replies

    20170720_114228.jpg
     
  2. Pete999
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    Pete999 Trusted Advisor

    Top Poster Of Month

    Location:
    Northampton
    That CU looks a right mess, I would be looking at the integrity of all connections paying particular attention to the N busbar, what a mess that is.
    5KW on a RFC are you sure?
    I foresee a CU change on the horizon. As well as some redirection of the RFC if that 5KW is correct, oh my.
     
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  3. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    Loose connection.
     
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  4. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    You sure it was 5kw that would be highly unusual if this is domestic.
     
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  5. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    You would need a 32A switch or contactor to control it.
     
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  6. SWD
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    SWD Gender neutral Electrician's Arms

    Location:
    London
    The neutral connection is the sheaving degrading or it is the flash from the camera?

    Nice amount of copper from the neutrals on show and the looped back live on the B6 breaker.
     
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  7. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    How have you come to the conclusion it may need rewiring.
     
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  8. Richard Burns
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    Richard Burns Trusted Advisor

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    From the pattern of heat distribution the neutral busbar terminal connection was loose or contaminated and the heat generated as the installation current passed through the resistance exacerbated the damage and increased the resistance and the heat and so on.
    That connection should be good for over 100A so overload is an unlikely cause.
     
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  9. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Definitely a loose connection and the link to the neutral bar appears to have got very hot.
     
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  10. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    See, that's what A3 CU's are all about :)
     
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  11. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Where was the combustion on the plastic cu?
    Loose neutrals and all that
     
  12. Pete999
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    Pete999 Trusted Advisor

    Top Poster Of Month

    Location:
    Northampton
    Sheaving???
     
  13. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Has the insulation at the top of Neutral gone dry/brittle ,
    can see where it's "flowed to blobs" .
    RCD end doesn't look as tarnished !
    (Nip it up - not completed?)
    (or later diagnosis/messing about-RCD-tripping)
     
  14. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Plastic will often lump together due to its molecular make up when exposed to heat. The heat here was insufficient to cause thermal breakdown of the molecules and hence no gas is released which would be required to create ignition.
     
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  15. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    As an a by, should the owner be told not to use the installation, until rectified?
    You been drinking already?
     
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  16. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Do a lot of fire risk assessments.
     
  17. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    What answer was a proper physics teachers response.
    Thank you sir. :D
     
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  18. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    What answer was a proper physics teachers response.
    Thank you sir. :D
     
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  19. Midwest
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    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Do you get twitching with a box of Swan Vestas in your hand :)
     
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  20. sheppertonspark
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    sheppertonspark EF Member

    Location:
    Shepperton, Middx
    To cover you behind send the customer a Danger Notice without delay. It looks too far gone to be cured by tightening the screw up. What do you mean by IR is open circuit (OC) ?, if it is how have you got satisfactory r1+r2 ? You have what is known as "guilty knowledge" of a potential fire risk. Ideally tell them it must be isolated and the C.U. replaced immediately, I realise that may not be practical, so send the Danger Notice and make it their problem not yours ! Sorry if I sound like an arse but where there's a blame, there's a claim !! .
     
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  21. SWD
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    SWD Gender neutral Electrician's Arms

    Location:
    London
    Sheathing, damn spell check on the Mac + Sausage Fingers.......
     
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  22. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    I suppose we are now implicated by also knowing and share the guilt. Oh oh!
     
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  23. ennaress
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    ennaress EF Member

    Location:
    Petersfield
    There are two immersion heaters in one insulated tank. The first is a Heatrae Centerbrand Superloy 800 and is 2.8kW @ 230V. The other is a Backer 2.7kW @ 230V.
    The owner was told that evening and I disconnected one of the immersions. I then replaced the burnt neutral with a new tail and terminated it to one of the non-melted points as a temporary, safe fix. The EICR has amongst over 20 other observations, a C1 for this....obviously!
    A replacement 7671-3 CU is going to be done. I'll also run the immersions on an indep circuit protected with a 20A breaker as will the oven.
    No - the outer sheathing had melted and globbed down the conductor.
    Yes - the R1-R2 were fine but rubbish / null IR readings which is a real head-scratcher and I'd welcome any sensible avenues of investigation.
     
  24. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    What do you mean by null IR readings.
     
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  25. Pete999
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    Pete999 Trusted Advisor

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    Location:
    Northampton
    Can you explain the last paragraph in greater detail? R1+R2 were fine but rubbish/null IR readings?????
     
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  26. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Measured on what ?
    , would it progress no further -Error ?
     
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  27. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Both immersion a on one circuit? How's that going to work?
     
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  28. Dave OCD
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    Dave OCD Electrician's Arms

    Location:
    Cornwall
    Business Name:
    Hendry Electrical Services
    Wire them through a 20a 2 way switch so one can have a rest every other day. :rolleyes:
     
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  29. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    I wouldn't rely too much on this 'danger notice' to cover your arse, I think it is more likely to be used to prove that you left a known danger in place rather than help you get away with it if the worst did happen.
    Don't forget that this 'danger notice' (if you are referring to what I think you are) is something invented by the nic which has no basis in the regulation or law.
     
  30. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Only the lower heater should be connected in a two immersion heater cylinder if no off-peak/E7 supply is available.
    The upper heater is only there to be a boost element in an off-peak/E7 setup. It will do little to no work if it is switched on at the same time as the lower heater, the heat from the lower heater will quite quickly operate the thermostat of the upper heater and switch it off. Also with modern immersion heaters the lower element can operate the overheat trip of the upper element and switch it off permanently (until reset)

    Why are you quoting the 230V power ratings? The public electricity supply in the U.K. is 240V, the mythical 230V only exists on paper and not in the real world. These immersion are will be operating at 3kW and using the lower power ratings will lead to you designing and installing a circuit with a small overload which is a dangerous situation.

    What is a rubbish/null IR reading? All of the IR testers I have used have only ever had a numerical scale so I haven't a clue what those readings equate to.
     
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  31. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    He's probably using 230 v because that is what we are taught to use from college and bs7671.
    We are required to record the nominal voltage on our test certificates as 230 volts and not the measured value.
    Also voltage drop calculations are based on 230 volts it's 3% of lighting etc based on 230 volts yes it takes the worst case scenario.
    Maximum zs values calculations require it to be 230 x 0.95.
    Where I do agree that most of the time the voltage is around 240-245 volts it's not the voltage we are told to use maybe common sense tells us different.
    Maybe it's not 'the real world' but it is whAt it is.
     
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  32. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Maybe a harmonized EUROPE ... or What it WAS ...
    (did we ever intend to comply -or just upped the + to 10%)
     
  33. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Yes it was to harmonise if you read page 316 of bs 7671 it was agreed by CENELEC within Europe from as early as 1988.
     
  34. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Politicians promises , (-sounds good-) !!!
     
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  35. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    latest one being corbyn's u turn on student fees. promise.. we'll scrap them.. now you students have voted labour, we wouldn't.
     
  36. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Was it about all debt , vs future debt ?
    (Just heard U turn ,and sighed/switched off)
    Vagueness is normal in their arean.
     
  37. ennaress
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    ennaress EF Member

    Location:
    Petersfield
    Typical....someone mentions a relatively minor point* about Voltage (each immersion carried a plate stating 230v...not because that's what I was taught at college - thanks all) and the thread goes way off into Labour party election promises...

    The IR readings for the Ring Final returned 0 and 5.5 and 5 MegOhms (must I state that these were for readings through L-E, L-N and N-E...?) and c.350 MOhms or thereabouts for the other circuits - 6A lighting and 2 No. 32A Radial (yes, I know a 32A on a radial is unusual). Either way, they're rubbish so that's why I assumed (wrongly) that you'd all be able to assume I knew what was a good, reasonable, unacceptable and utterly rubbish reading.

    *Please - do not start arguing the **** - of course Voltage is a critical element of everything we do - I mean minor as in the relevance to the problem - low/no IR readings.
     
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  38. DPG
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    DPG Electrician's Arms

    Location:
    S Yorkshire
    Are you saying the IR reading between Live and Earth on the RFC was zero ohms ??
     
  39. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    On the ring final did you unplug / remove all loads to get the L/N reading.
     
  40. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    We are given 230V as the nominal voltage yes, but that is nominal.
    Nothing in the regulations tells us that it must be used to calculate current ratings, as far as I know the regulations don't tell us anything about how to calculate current.
    The regulations do state at various points that nominal values should be used when no better information is available, the actual voltage is always readily available to us.

    The regulations do however require that we do not allow small overloads to be designed in to a circuit.
    Designing a circuit based on 230V power ratings when the actual voltage is higher will lead to such small overloads being designed in to the circuit, which is dangerous as the ocpd will not operate on such overloads.
     
  41. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Still confused with order
    Ring Final returned

    0 and 5.5 and-- 5 MegOhms ...
    L-E, ..L-N and N-E...?
    If N-E have not been isolated L&N swapped ..
    (or is it just LE,LN&NE sequence off)
     
  42. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    I don't find it confusing.
     
  43. ennaress
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    ennaress EF Member

    Location:
    Petersfield
    Zero was the reading for Ring Final between Line/Earth. 5.5MOhms was the reading for Line/Neutral. 5 MOhms N-E. c.350 MOhms or thereabouts for the other circuits. This was a soft test (250V) - and yes I know what 7671 says...but disconnecting all loads was not practical at the time. I knew the CU would have to be replaced and that the circuitry was shot due to the burnt N bar so I hoped a soft test would suffice knowing a new CU would then have to be fully tested with 500V DC.
     
  44. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    If you haven't disconnected all loads how have you got a L/N reading and differing L/E and N/E readings. You should have used 500v it would have done no harm.
     
  45. DPG
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    DPG Electrician's Arms

    Location:
    S Yorkshire
    But the zero ohm reading shows that there is either a fault or something is still plugged in. Without unplugging everything how will you know which it is? The test result is meaningless.
     
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