Green Goo C2

Hi guys.

I came across the dreaded green goo yesterday on a domestic EICR in a rental. I have coded it as a C2. I believe that is correct from what i have read on-line re can cause over heating if it causes an arc at the terminals.  I have also said the general guidance is to rewire although it may be able to be cleaned off and monitored with regular inspections. Any thoughts please.

I know this has been discussed many times on here but couldn't get anything up on a search.  Cheers

Gary

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  • I've not seen it, so could be totally wrong about what condition the one you have seen.

    If the insulation resistances are high (50Mohm+), I would probably give it a C3, with a recommendation to inspect more frequently. I've come across a number of installs like it, and none of them have shown any breakdown of the insulation. Maybe 10 years ago, there was an article in the wholesalers comic, from Napit IIRC, saying it is the elastomer breaking down, and it isnt immediately dangerous. A quick search, and I think it is the article linked below.

    And Prysmiam have a similar, though more cautious article linked below. Starngely it says the goo is non-conductive, but later says it can cause tracking between terminals.

    The more cautious tone will definitely carry on with more recent reports, along with younger inspectors who havent seen it before condeming the install immediately. Each install will need specific inspection to see what the outcome will be, thats where your experience is needed.

    Napit advice

    Prysmian advice

  •  Thanks Alan.  The Prysmian article was the one that i read and based my code and advice on. The insulation resistance readings were not too bad to be honest,(about 12 megohms) but the terminals in the ceiling roses are a  mess.

    Gary

  • I have seen that sort of thing, and looking quite a bit worse actually - it is very much the plastic in the cables de-plasticising, but it seems to affect the ends first - maybe air or damp accelerates it, I don't know,  so if you cut a piece in the middle  you may find it less affected. Cleaning off with methylated spirits makes it nicer looking but electrically I found it to be  OK, just ugly  and nasty to handle when sticky.

    It will be of an age that lights probably do not have CPCs and on a ring it may be a bit thin on the earthing - the imperial equiv of the 1mm2 cpc. so a rewire soon is on the cards, but maybe not the immediate danger that some more sensational sources suggest.

    The cable maker's legal team want to avoid all liability, and maybe like to sell more cable, so  will err on the safe side - the rewire is not theirs to pay for after all  - on the other hand I suspect any plastic DNO cables of the same era will be run to failure and then quietly replaced.

    (Mind you, in  case I sound too offhand, I have slowly got rid of all of it in my house  now, apart from some stripped and cleaned  offcuts that are  holding the rabbit fence together and things in the garden tied to bamboo canes)

    Mike.

  • Starngely it says the goo is non-conductive, but later says it can cause tracking between terminals.

    The more cautious tone will definitely carry on with more recent reports, along with younger inspectors who havent seen it before condeming the install immediately. Each install will need specific inspection to see what the outcome will be, thats where your experience is needed.

    Napit advice

    Prysmian advice

    The Prysmian article says that the plasticiser itself is non-conductive, but the green goo is a mixture of plasticiser and copper oxide ... and that is conductive. The NAPIT article says the green goo is non-conductive

    Hence, these two references don't agree on a basic issue: is green goo conductive?

    Regardless of the answer to that question, any sticky contaminant potentially permits an easier build up of particles, that could be conductive, or conductive when damp) and therefore it's possible that any electrical connections that the substance runs upon, or in, is potentially exposed to a higher degree of pollution (that can cause electrical tracking etc.).

    Therefore it might be argued any such equipment is being used outwith its intended (specified) installation conditions (fundamental requirements, Regulations 132.5.1, 133.3, also consider Regulation 133.1.3).

    If the insulation resistances are high (50Mohm+)

    That is definitely a good idea to help identify whether there are any immediate issues ... it's more difficult, however, to make long-term recommendation other than replacement is recommended, perhaps - certainly at least more frequent inspections.

    This I think aligns with the guidance provided in Section 7.5 of IET Guidance Note 1 Selection & Erection (1st para of page 107 of the 9th Edition 2022):

    As only the plasticiser is removed from the insulation, it is not expected that the insulation resistance of the cable will be affected if the cable is not disturbed, but this cannot be guaranteed and a test should be carried out. The cable condition should also be monitored over time in regular periodic inspections, perhaps making the recommendation for more frequent inspections.

    Both GN1 and the IET Guide to Cables and Cable Management recommend the substance is removed from accessories to prevent contamination of terminations etc. - and also advise suitable safety precautions because of the toxicity of the goo.

  • Suppose that you have just bought a new flat and you find that. Would you leave it? I think not. I'd like to say C2. Yes, C2 rather than C3 'cos there is no proper support for the dangling cable. The neutral chockblock looks particularly unsatisfactory. And I trust that the two colours notice has been affixed at the origin.

  • And I trust that the two colours notice has been affixed at the origin.

    Haha. No need for that now.

  • 'cos there is no proper support for the dangling cable

    That's a whole other issue than the 'goo', and certainly worthy of note.

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