blue negative wires on wrong way round and power surge query


Postby mandyb » Mon Nov 12, 2007 9:13 pm

i have been having electrical work done in kitchen and one day my washing machine lights were flashing in the morning, while i was at work the electricians came in again and did some more changes and when i plugged the washing machine in that evening the switch tripped and the washing machine is now dead. everything else i plugged in that socket tripped the switch too. i had a washing machine engineer out and he said a power surge from the temporary electrics had killed the machine so i got on to the electricians and they have told me you can't get a power surge from the electrics in the house only from the main elec company and the only thing they did wrong was to put the blue negative wires on the wrong way round and that would not have caused any problem with my machine-is this right?
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Postby sparx » Mon Nov 12, 2007 11:46 pm

Hi Mandyb,
they are right abt 'power surge' but if they got Blue[Neutral] crossed with grn/yel [Earth] then anything plugged in would trip your RCD. In a washing m/c. there are mains filters fitted between the 3 wires to stop the motor interfering with TV's ect. these can be blown by a wrong connection such as this.
If so the filter unit is very cheap to replace itself but it is possible other items also damaged ie programmer, your 'engineer' could have been more explicite as to what has 'died' in the m/c. though,
how to prove what happened is difficult but I would get a repair quote from W-M repairer & present it to electricians for comment! If they are registered 'domestic Installers' they must have insurance,
regards SPARX
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Postby kuzz » Mon Nov 12, 2007 11:55 pm

Sounds like they mixed the neutral & earth up. A silly mistake & quite inexcusable to be left that way as all work should be tested. However, the tripping would be an inconvenience rather than a danger & as both neutral and earth are at zero potential it would make no differents or damage your washing machine in any way. As for power surges from temporary electrics, what a joke! I think he's seen you've been having work done & tried to pin the blame on them! an appliance can only draw a certain amount of current (Depending on it's resistance) I'm quite sure your washer did not grow eyes, see it was connected on a temporary basis & decide to suck more current than normal to damage itself!
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Postby kuzz » Tue Nov 13, 2007 7:51 am

Sparx, I don't agree with you, can you explain how a humble washing machine can tell the difference between a neutral at zero volts and an earth at zero volts and why this technology is not taken out of washing machines and used in test equipment?
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Postby sparx » Tue Nov 13, 2007 10:24 pm

Filters are designed using chokes,capacitors ect and are different between L & N and L & E called PI networks. N & E are not the same thing even with a TN-C-S supply, they can be, under fault conditions, up to 50 Volts apart at the end of a circuit, which is why we have to calculate/measure earth fault loop impedances to ensure we don't go above that touch voltage before disconnection of supply.
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Postby kuzz » Tue Nov 13, 2007 11:56 pm

Current leading or lagging the voltage so very very irrelevant when were talking about the potential it's at. Obviously neutral and earth are not the same thing in a tn-c-s or it would be a tn-c which for the record doesn't ruin washing machines either. I wasn't suggesting the washing machine guy was trying to scam anyone so much as disguise his mass incompetence.
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