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- 21 Dec 2007
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Hi, I would like something to be confirmed before I blow myself up!
First let me set the scene... My property is suffering from intermittent nuisance tripping, sometimes it happens nightly, and sometimes not for weeks, and there is no rhyme or reason (such as specific times or appliances or weather etc).
To make matters worse, the property is in France and has a 30ma RCB built-in to the electricity companies main incoming isolator, so there is no way I can bypass or split it to help pinpoint the cause (I can't speak french yet by the way, and couldn't afford to call out an electrician even if I knew how!).
An added complication is that it's a 3 phase supply feeding 6 single-phase consumer units plus some 3-phase sockets (property was previously a lorry yard which I'm converting to caravan storage and overnight parking). The property is quite old, the wiring is maird', and radial, with some going externally underground to an out-building. When initially trying to find the problem I discovered that one of the phases contacts in the old isolator were welded shut therefore everything on that phase was still live even with the isolator tripped off! I got the power company out and they installed a new one, so I'm reasonably sure the problem is my equipment and not theirs.
Due to the intermittency I think I'm going to have to 'pre-load' the earth leakage current to the point where the faulty item will definitely cause a trip when I connect the offending item/circuit. My ohm's law is nearly 50 years old, but having dusted it off it seems like I should be able to use a 10K 10w resistor to give about 25ma max in series with a 250K variable resistor (if I can get a 10w one) to allow the current to be reduced down to about 1mA (I've 'assumed' 250v instead of 230v for a bit of a safety margin) and with an AC milliameter in series with the resistors so I can see how much added leakage is needed to cause tripping and therefore get a rough idea what the real leakage must be (30mA minus the pre-load value).
So my first question is... should that work?
At the moment I dare not leave the property for any length of time - such as going to England - without risk of another nuisance trip taking out all my local and online security and CCTV etc (browse to www.electroguard.com if you're interested) and spoiling fridge and freezer contents.
So my second question is...
Until such time as I can track the problem down could I use the same setup between L and N instead of L and E to provide an opposite 'offset' leakage and therefore reduce the possibility of tripping in my absence by effectively increasing the required tripping current up to about 55mA (RCD 30 mA + 25mA offset)?
Lastly... I seem to remember that 35mA was accepted as the fatal 'dose' so is presumably why 30mA protection was adopted as standard, but with the premises being vacant would a tripping leakage of less than 60mA still provide safe protection for the property?
BTW - I deliberately posted in the UK and not the 'Overseas' category (even though the property is overseas) because the actual problem and questions are not really location specific, and therefore are answerable by non-french expertise.
Thanks in advance for any advice.
First let me set the scene... My property is suffering from intermittent nuisance tripping, sometimes it happens nightly, and sometimes not for weeks, and there is no rhyme or reason (such as specific times or appliances or weather etc).
To make matters worse, the property is in France and has a 30ma RCB built-in to the electricity companies main incoming isolator, so there is no way I can bypass or split it to help pinpoint the cause (I can't speak french yet by the way, and couldn't afford to call out an electrician even if I knew how!).
An added complication is that it's a 3 phase supply feeding 6 single-phase consumer units plus some 3-phase sockets (property was previously a lorry yard which I'm converting to caravan storage and overnight parking). The property is quite old, the wiring is maird', and radial, with some going externally underground to an out-building. When initially trying to find the problem I discovered that one of the phases contacts in the old isolator were welded shut therefore everything on that phase was still live even with the isolator tripped off! I got the power company out and they installed a new one, so I'm reasonably sure the problem is my equipment and not theirs.
Due to the intermittency I think I'm going to have to 'pre-load' the earth leakage current to the point where the faulty item will definitely cause a trip when I connect the offending item/circuit. My ohm's law is nearly 50 years old, but having dusted it off it seems like I should be able to use a 10K 10w resistor to give about 25ma max in series with a 250K variable resistor (if I can get a 10w one) to allow the current to be reduced down to about 1mA (I've 'assumed' 250v instead of 230v for a bit of a safety margin) and with an AC milliameter in series with the resistors so I can see how much added leakage is needed to cause tripping and therefore get a rough idea what the real leakage must be (30mA minus the pre-load value).
So my first question is... should that work?
At the moment I dare not leave the property for any length of time - such as going to England - without risk of another nuisance trip taking out all my local and online security and CCTV etc (browse to www.electroguard.com if you're interested) and spoiling fridge and freezer contents.
So my second question is...
Until such time as I can track the problem down could I use the same setup between L and N instead of L and E to provide an opposite 'offset' leakage and therefore reduce the possibility of tripping in my absence by effectively increasing the required tripping current up to about 55mA (RCD 30 mA + 25mA offset)?
Lastly... I seem to remember that 35mA was accepted as the fatal 'dose' so is presumably why 30mA protection was adopted as standard, but with the premises being vacant would a tripping leakage of less than 60mA still provide safe protection for the property?
BTW - I deliberately posted in the UK and not the 'Overseas' category (even though the property is overseas) because the actual problem and questions are not really location specific, and therefore are answerable by non-french expertise.
Thanks in advance for any advice.