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Why is the kitchen sink supposed to be earthed?

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  • 16-12-2011 12:25am
    #1
    deandean
    Registered Users Posts: 2,234 ✭✭✭


    I got a cracker of a shock the other day: the 10-year old washing machine blew a 'stat and BOILED a load for about 90 minutes (my favourite winter coat of course, on a 30Deg wash).

    I came in and the kitchen was full of steam. I saw what had happened and the blood-red soup in the washing machine that used to be my cost, kicked the machine a few times, turned it off. (reckoned it decided to get one back).

    The washing machine is in the usual slot under under the kitchen counter so I got it a bit out and then using the counter/kitchen sink as leverage, got a good hold of the washing machine and BZZZZZTTTTTT big shock up one arm, through the chest, down t'other arm and to earth via the sink.

    The washing machine was full of steam so I guess there was a leakage from a live connection to the machine body or the likes.

    There's a modern consumer board here with 20A MCB and 40mA RCD on the kitchen sockets.

    So I was thinking: why the flock is a kitchen sink earthed? If it hadn't been earthed I wouldn't have got anything like the shock I did. I reckon you're much safer treating a kitchen sink as 'insulated' and don't connect it to anything.

    Any thoughts; I am here with the wire cutter:D

    Dean


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    #2
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    deandean wrote: »
    I got a cracker of a shock the other day: the 10-year old washing machine blew a 'stat and BOILED a load for about 90 minutes (my favourite winter coat of course, on a 30Deg wash).

    I came in and the kitchen was full of steam. I saw what had happened and the blood-red soup in the washing machine that used to be my cost, kicked the machine a few times, turned it off. (reckoned it decided to get one back).

    The washing machine is in the usual slot under under the kitchen counter so I got it a bit out and then using the counter/kitchen sink as leverage, got a good hold of the washing machine and BZZZZZTTTTTT big shock up one arm, through the chest, down t'other arm and to earth via the sink.

    The washing machine was full of steam so I guess there was a leakage from a live connection to the machine body or the likes.

    There's a modern consumer board here with 20A MCB and 40mA RCD on the kitchen sockets.

    So I was thinking: why the flock is a kitchen sink earthed? If it hadn't been earthed I wouldn't have got anything like the shock I did. I reckon you're much safer treating a kitchen sink as 'insulated' and don't connect it to anything.

    Any thoughts; I am here with the wire cutter:D

    Dean

    A properly working RCD on the circuit the washing machine was supplied from would of tripped if the washing machine had an earth fault, assuming the washing machine itself and its socket, is properly earthed.

    So possibly either the sink was live, or more likely the washing machine was not properly earthed.

    The reason all metalwork in a house should be earth bonded is to do with the houses being neutralised. Neutral into the house fails out beyond the neutralising point, and all earthed metal in the house will go above ground potential, what level depending on the load that is on in the house at the time, and how good a connection the earth rod is making to ground, but this is not usually that great with a single earth rod, now isolated from all other earth rods on the esb system because of the broken neutral.

    If all metal is earthed properly, then it will all at least be at the same potential voltage, minimising shock risk.


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    #3
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,592 Mod ✭✭✭✭2011


    Welcome back Robbie :)

    There's a modern consumer board here with 20A MCB and 40mA RCD on the kitchen sockets.
    I guess you mean 30mA?
    If all metal is earthed properly, then it will all at least be at the same potential voltage, minimising shock risk.
    As well as keeping all extraneous metalwork at the same potential, it will also ensures that the protective device operates in the event of an earth fault.


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    #4
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    Welcome back Robbie :)

    Thanks 2011:)


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    #5
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    Yes the local bond is designed to minimize the shock risk

    Sounds like there was a problem with earth on washer


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    #6
    deandean
    Registered Users Posts: 2,234 ✭✭✭deandean


    Yea I see fully what you mean, the washer casing should be @ some potential as the sink and I shouldn't have got the shock.

    I can only think that with all the steam in the washing machine, maybe I contacted a part that wasn't earthed or something.

    I checked the socket and sink bonding and the RCD (yes 30mA not 40), all OK.

    Reckon that washing machine had it in for me after the kicking I gave it.


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    #7
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    The sink should only need bonding if its actually extraneous


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    #8
    10-10-20
    Registered Users Posts: 7,162 ✭✭✭10-10-20


    M cebee wrote: »
    Yes the local bond is designed to minimize the shock risk

    Sounds like there was a problem with earth on washer

    Either that or when he pulled on the washer, it caused the live to touch the washer chassis at that point, but not beforehand.

    deandean - are you planning on diving into the washer to identify the cause?


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    #9
    deandean
    Registered Users Posts: 2,234 ✭✭✭deandean


    10-10-20 wrote: »
    deandean - are you planning on diving into the washer to identify the cause?

    No, I normally would get stuck in but needed a new washing machine rightaway; I threw the offending item into the car and WEEE'd it for a new Bosch. So the old one is on it's way to Wales or China or somewhere to be recycled into iPhones.


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    #10
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    10-10-20 wrote: »
    Either that or when he pulled on the washer, it caused the live to touch the washer chassis at that point, but not beforehand.

    This would be a non issue on a properly earthed machine, using a properly installed socket circuit. For the OP event to happen would require a machine with a non earthed frame, or the entire machine not earthed at all, assuming the sink is bonded and not live itself.


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