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Corroded MCB - what happened

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  • 21-08-2021 1:32pm
    #1
    karolaug
    Registered Users Posts: 19 ✭


    Hey,

    I have noticed one of MCBs in my panel was buzzing under load. I have replaced it and I noticed that the old one had corroded copper contacts on both sides and some brown fluid leaked from it. I opened it up and discovered that only the contacts were corroded and the rest of the internals were stained. (see pic).

    What caused it? Is it a sign of a bigger problem?


    Thanks

    PXL_20210821_110704358.jpg




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    #2
    10-10-20
    Registered Users Posts: 7,168 ✭✭✭10-10-20


    Curious. Can you upload a larger version of that image?

    Plus tell us about the panel in terms of location and age. Residential or comm? Old or now house? Is it on a cold wall or have any possible moisture ingress?



  • Options
    #3
    karolaug
    Registered Users Posts: 19 ✭karolaug


    It is residential panel. Not new, but I don't know how old it is, probably installed in 2000s. It is installed on internal wall and there is no evidence of any water ingress inside the panel.

    As you can see from the pictures both copper contacts are corroded, it looks like independent of each other. Even if the connected cable was pulling water I can't explain the corrosion on the bus (lower) side.

    There was a brown stain below the MCB on the panel. It looked like the rust stain but I just wiped it with my finger. If the water was responsible why the steel parts (screw and the contact) are not affected and only the copper part was eaten by it?

    PXL_20210822_082714318.jpg
    PXL_20210822_082659396.jpg
    PXL_20210822_082654967.jpg
    PXL_20210822_082641957.jpg




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    #4
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭2011


    It is possible that the MCB was corroded when installed. Perhaps it has been in an electrician’s van for years or was second hand. The electrician may have been completely unaware that the internals were in this condition at the time of install. It may be worth opening up another MCB on the same board.



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    #5
    10-10-20
    Registered Users Posts: 7,168 ✭✭✭10-10-20


    If it's oxidising to that colour, it's not copper. That's likely to be a ferrous material - light steel. The copper parts which I can see - the wiring and the balance coil are copper and unaffected, but the coil is enamelled. The arc suppressor is clear of corrosion interestingly, but may be a better quality steel (more carbonised).

    Given the way that the oxidation is all to the front of the MCB, I'm going to guess that this could be dew-point related surface corrosion. Perhaps the house was damp/unheated for a duration and moist air was being pulled in through the panel by a void, etc. Just a guess.



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