RCD will not reset

[lj329]

Hi All

I know this is a favoutite topic and I have looked through all the past posts, but would still appreciate some opinions.

My CU is a Wylex split load NHRS9SL, with a 80A/30mA WRS 80/2 RCD.

The unit is about 5 to 6 years old - fitted just before we moved in I believe.

The RCD protects all the ccts apart from the lights. The RCD has always occasionally tripped, but over the years the frequency has increased to just about every day last week, and now it will not reset at all.

Here is what i have tried:

Switch off all the protected MCBs - still trips
Unplug everything, turn off sockets, including cooker, boiler, mini CU in garage - still trips
Take off front of CU, disconnect all the live tails to the top of the MCBs - still trips.

I am getting a Spark out on monday, but is there anything else I can check?

I am running a extension lead from next door to run the tele, but boy I am getting grief for not sorting it sooner.

thanks

Lee

 

[ColJack]

as we're not there to physically see the installation we can only offer guess work at best..

do you have any outside lights perhaps running off the sockets? ( plugged in ir wires through a FCU? )
immersion heater?
shower?

any item that has water in it or is exposed to water is a possible suspect..
it could be that your light has water in it ( and as the weather has been particularly bad recently and your problem has escalated recently that would be my first point of call to check. ).
it could be that your immersion heater is cracked and water has gotten into the element..
washing machine? did you just switch off or unplug it? some older sockets only had single pole switching which means that th neutral is still connected if it's just switched off..
shower may be leaking.. and so on..

it's also equaly possible that you have this problem...

View media item 9882
things like to eat insulation for some reason and then damp gets into the cables.....

 

[dannyboi2003]

If you have already been in the CU and disconnected the live out from the mcb's then you were on the right track. Go back and disconnect the neutral for each circuit in turn as it sounds like a N/E fault. When you find the faulty circuit leave it disconnected and isolated until your sparks can have a look. If you don't feel competent do do what i sugested then best to leave it to your sparky.

Let us know what the problem was

 

[ccrowe]

I am running a extension lead from next door to run the tele, but boy I am getting grief for not sorting it sooner.

Assuming next door is on a different phase from you, you're introducing a 400v potential to your house. If you do manage to restore power over the weekend, make sure the extension lead is disconnected immediately. If not, then disconnect it when your spark starts work on Monday.

 

[RMS]

Possible N-E fault.

Although the RCD might be faulty. (maybe due to the constant tripping).
Have you switched off the main switch and then reset the RCD? Does it reset?

 

[lj329]

Thanks for the replies,

I have checked out the outside lights etc, although they run off the mini CU in the garage, which is off. I don't have an immersion or electric shower. Everything else is unplugged. I have also turned off the main switch on th CU, still bloody trips.

How do I remove the neutral from the MCBs - as far as I can see there is a live tail connection at the top and I assume the neutral connects through the rail (busbar?) that the MCB sits on. I can't see any other tails connected.

Thanks for the advice on the extension lead, don't worry though I am only running the tele, dvd, cable box, stereo, iron, kettle.............

 

[flameport]

How do I remove the neutral from the MCBs

The neutrals are not connected to the MCBs, there will be a separate bar where they all connect. Usually at the top of the CU.

 

[RMS]

If the RCD still trips when the main switch is off then the RCD is probably faulty.

 

[bongos]

If the RCD still trips when the main switch is off then the RCD is probably faulty.

Could a N>E fault on a TN-C-S system still cause an RCD to trip even if the main isolator was off? (I'm asking because these faults always confuse me not because it is neccessarily the fault!)

 

[ColJack]

if the MAIN isolator is off then NO rcd will ever trip.. even if it's got a direct short live to earth..
no current is flowing through the coils AT ALL..

they are electromechanical devises that need a live supply to them to operate.. you might as well ask if your vacuum cleaner will work if it's unplugged..

 

[SparkyNinja]

Just to add-on to ColJack there, when you test the RCD with the DP main switch off the Neutral is also isolated and so N-E faults can be omitted if the RCD still trips.

If it trips with the main switch off then change it. But do test your main switch first before spending money.

 

[ColJack]

widdler? what are you on??

if it trips with your main switch off, GET THE DNO OUT... FAST!!!..
either your main switch is broken and is still on even though the handle is off, or they've wired your supply wrong and the earth is live...

with the main switch off.. there is NO POWER to the house so NOTHING electrical will work.. this goes for RCD's as well since they need power to operate in the first place..
they WILL NOT!!!! trip with the main switch off unless there is a serious fault and you have a back feed somewhere ( like a cable with 2 plugs on, one in your socket, one in your naighbours.. )

 

[SparkyNinja]

I think you mis-understood my point there.. calm down


I was interepreting the understanding that if you are soley testing for a N-E fault, isolating the main switch will isolate the neutral, meaning the RCD should not trip if there was a N-E fault. But if it still trips with the main switch off, then a N-E fault is not the cause.

 

[ColJack]

I was interepreting the understanding that if you are soley testing for a N-E fault, isolating the main switch will isolate the neutral, meaning the RCD should not trip if there was a N-E fault. But if it still trips with the main switch off, then a N-E fault is not the cause.

Ok, so you don't see the problem with the statement in bold?
how can an RCD operate AT ALL if there is no power to it?
it's not like the things are wind up or battery operated..

with no power to it at all, an rcd will not trip even if you push the test button.. which is the point I was trying to make..

 

[sparkyspike]

It's the word 'trip' that is causing confusion. To the OP: Do you mean that the RCD won't reset when you say it 'trips' with the main isolator open?

This would indicate a broken RCD. Probably caused by repeatedly resetting the device with a fault still present.

However, you still need to clear the fault before fitting a new one.

If you have a multimeter, it may be worth disconnecting all of the neutrals in the RCD neutral bar and testing resistance to the earth bar. You should find the fault this way. At least then you can show the spark where the problem lies. If you can't find a fault (a low resistance reading) then you may need to use an insulation resistance tester.