Can any one advise? I suspect I have a problem with the electricity wiring in a house I recently moved into. Most of the time there is not a problem, but sometimes when we plug in our iron, the master trip switch is activated. I thought at first that there might be a problem with the iron, but this also happens if we turn on the immersion heater or sometimes using the hoover.
what I dont understand is why the master trip would activate rather than the plug fuse or the trip switch for the particular circuit? Can anyone shed any light? Secondly, how do I go about diagnosing such a problem?
It's presumably because the "master trip" is an RCD which trips on a small leakage current to earth whereas the "trip switch" for the particular circuit is an MCB which will trip on an over current to protect the wiring.
It is now no longer recommended to have a single RCD protecting your whole installation as you have (unless you have a TT system with a local earth but that is quite unusual). This is because the risk of being plunged into darkness when it trips is quite significant. You might want to consider changing your Consumer Unit ("Fuse Box") for this reason though it isn't absolutely neessary.
Regarding your present problem there are various possibilities:-
Your iron, immersion heater and hoover really *are* faulty. This is quite possible, the heating elements in irons and immersion heaters are quite prone to the type of fault that will trip an RCD. As long as the earth is sound it's not particularly dangerous but should be fixed. Hoovers do tend to suffer from flex failure due to the way they are used.
There is leakage current from other equipment (PCs in particular) that adds up to nearly enough to trip the RCD, then the addition of a tiny bit of extra leakage, which would otherwise be no problem, from the iron trips the RCD. Do you have a lot of PCs and similar equipment?
There is faulty wiring or damp in the wiring which is causing enough leakage to trip the RCD sometimes.
The RCD has got 'super sensitive' and is tripping when it shouldn't.
Old or new property? Do you know if it's been rewired? How old is the electrical installation?
Do you know what sort of earth trip you have? Very old systems have what is known as a voltage-operated trip, prone to all sorts of problems, not the least of which is that they may not actually be much use when something serious goes wrong! These types will be a completely separate item, and not incorporated in the consumer unit.
Because they are protecting you against earth faults, and not overloads. They require a much smaller earth fault current to operate than is require for overload protection.
Not being rude, but if you don't understand such a basic difference between earth faults and overloads, then you really shouldn't be contemplating trying to diagnose the problem.
haha, thanks for all the comments. Indeed, I should not be trying to diagnose the problem. I guess I am trying to get to the stage where I understand what the likely problem is so I can make a judgement on whether to get in an electrician or buy a new iron or something else.
To answer some of the other points, yes, I do have some computer equipment that is always on, including a server, DLAN connectors, wireless router etc. I will power all these down and try again to see if it still trips. If it doesn't and hence points to the PC and other kit, what should my next steps be?
oh, and the house was new in 86 so not too old. Thanks again.
haha, thanks for all the comments. Indeed, I should not be trying to diagnose the problem. I guess I am trying to get to the stage where I understand what the likely problem is so I can make a judgement on whether to get in an electrician or buy a new iron or something else.
To answer some of the other points, yes, I do have some computer equipment that is always on, including a server, DLAN connectors, wireless router etc. I will power all these down and try again to see if it still trips. If it doesn't and hence points to the PC and other kit, what should my next steps be?
oh, and the house was new in 86 so not too old. Thanks again.
get a basic multimeter and test the iron for E to L&N resistance, with the iron not plugged in, and set so it would be heating if it were plugged in. This is a low votlage test rather than a megger test, but IRL can pick up almost all leakage faults, if not quite all. Same with your immersion if its on a mains plug. Hoover too, if it has an earth wire, though most dont.
This will tell you if those appliances are faulty. Chances are they are, and need fixing.
Just a note re ELCBs for the technical: while they arent perfect, their nuisance tripping rate is extremely low in comparison with RCDs, which are one pita.
And this probably isnt an ELCB, 3 appliances that all trip an ELCB would be a fairly unusual situation.
In our case it was a premature aging of a fairly new iron (ie somehow or other the internal water seals in the iron were failing. Running it through its own rcd adapter socket didn't solve the problem. Buiying a new iron did.
but this also happens if we turn on the immersion heater
Common reason behind rcd nuisance tripping is that resistance live-to-earth or neutral-earth is no longer near infinite. If your iron is still plugged in, even if switched off (most sockets only switch the line side), then that low leakage resistance is still present & seen by the RCD. Switching on the immersion heater adds another neutral-earth resistance (which may change as the immersion heater heats up). Anything else plugged in adds its tuppence worth of N-E resistance too. In the end the leakage current may exceed 30mA & the RCD trips.
To be sure it is the immersion heater, or whatever, causing the trip you need to unplug the iron & anything else suspect. BTW it won't happen in reverse as the immersion heater is switched through a double pole switch, disconnecting both L & N.
We've had this type of fault with 2 newish irons after a year or 2, so I presume they aren't made to last anymore & it is now a common mode of failure.
HTH helps but please note it could be some more complex fault.
On 23 Feb 2006 14:35:07 -0800 someone who may be "jim_in_sussex" wrote this:-
RCDs measure any difference between the currents flowing in the live and neutral conductors. If a set difference is exceeded then they trip. The most usual setup is for "instant" tripping with a difference of over 30 milliamps. If both your "master trip" and RCD adapter were of this sort then they would both trip at much the same time.
To avoid this the "master trip" can be of a sort with a time delay.
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