Main RCCB keeps tripping

[bullethead123]

HI all,
This morning I noticed that the main consumer unit RCCB (Crabtree 63A 30mA trip)was off. It would not reset until I had switched the CB for the kitchen power points off. When I switched the Kitchen CB back on, the RCCB tripped again. I then unplugged everything in the kitchen and got all circuits working.
On plugging stuff back in, I found a plinth heater, the kettle, and the washing machine, when plugged in individually, each tripped the RCCB. I then tried the kettle in a couple of lounge power points (a different circuit to the kitchen) and all was fine.
After scratching my head I used an extension lead to try the washing machine (the washing machine was the only appliance which had been operating this morning) from the same two power points in the lounge and the RCCB tripped both times.
Though the washing machine may seem to be the main culprit, the fact that the plinth heater and the kettle also trip the RCCB would seem to indicate that it is not.
I have removed the front of the consumer unit and visually inspected the RCCB - It looks fine/no smells of burning.
Could it be that the RCCB may have developed an enhanced sensitivity?
Any confirmation (or debunking) of my theory welcome.
Chris

 

[bernardgreen]

A fault that is a connection between the Neutral and the Earth will not cause an RCD to trip until there is a load on one of the circuits protected by the RCD.

Some of the load current on the Neutral goes through the fault to Earth and thus bypasses the sensing coil on the RCD. This unbalances the sensor ( Live current not equal to Neutral current ) and thus the RCD trips.

.

 

[bullethead123]

Thanks for the tutorial on RCDs Bernard.
I thought I'd posted before but, because the internet was down, it didn't post.
In the meantime I have disconnected lives and neutrals (at the consumer unit) from each circuit fed from the RCCB individually in turn. Each time, plugging in the washing machine causes the RCCB to trip.
I would have thought that, if there is a neutral-to-earth fault, isolating circuits in this manner would result in the RCCB NOT tripping in at least one case?
Am I missing something?
P.S. I do have some electrical experience, having trained as a factory electrician many years ago.
Chris

 

[bernardgreen]

If the Live and Neutral to the washing machine socket are both fully disconnected at the consumer unit then in theory plugging the washing machine in cannot result in a trip of the RCD,

In practise there can be sneak circuits involving the Earth conductor ( CPC ) to the socket and the "Earth" conductor from an appliance that is "earthed" via the pipework bringing water and/or gas to the appliance.

The other possibility is that when testing the wrong Neutral is accidently disconnected in the consumer unit ( been there, trusted the Neutrals were arranged in the same order along the Neutral bar as the Lives were in the MCBs. The Neutral ends of a couple of ring finals were not in the same place on the bar. )

 

[bullethead123]

Thanks for your reply Bernard.
I made sure I disconnected the correct cables. I can see where the black & red meet at the outer sheathing of the T&E - so that's not a possibility.
Since my last post I have been testing the kettle in different sockets and now it doesn't cause a trip at all. Similarly with the plinth heater.
The washing machine however, trips the RCCB immediately, regardless of which circuit it is plugged into.
Also, whereas earlier this morning it would take a minute or two before the RCCB would reset, Now, after each trip it resets immediately. Does this indicate anything to you?
I'm beginning to suspect the washing machine again.
I reckon I should wait til my neighbour gets in tonight and ask him if I can plug the washing machine into his power circuit (assuming he's got a 30mA RCCB) to prove it one way or t'other.
What do you think?
Thanks for your help,
Chris.

 

[bernardgreen]

Am I right in assuming that the washing machine does not ( did not ) trip the RCD when plugged into a socket that is ( was ) disconnected ( Live and Neutral ) at the consumer unit ?

If it did not trip when plugged into a socket that was disconnected at the consumer unit then the washing machine is the most likely culprit..

 

[bullethead123]

Am I right in assuming that the washing machine does not ( did not ) trip the RCD when plugged into a socket that is ( was ) disconnected ( Live and Neutral ) at the consumer unit ?

I didn't actually try that Bernard.
I did manage to open the door of the mid-cycle washing machine by draining it manually and pressing the 'STOP' button whilst plugging it in. It is now plugged in and (it says it is) ready for use. Maybe it is a specific point in the cycle when the fault becomes apparent. I'll put another wash on and keep an eye on it.
I'm almost certain it's new washer-dryer time. it is 5 years old!
Bye-Bye £500.
Thanks once again for you help - I've learned quite a bit this morning
Chris.

 

[jj4091]

It is quite common for washing machine, like other appliance, water heating elements to fail. Disconnect & insulate the wires from each terminal & try again. It probably will not complete the cycle but come up with a heater fault code & if it does not trip then a new element will probably be needed.

 

[bullethead123]

Thanks JJ,
If it was a couple of years old I'd try some further diagnostics as you suggest but given that it's 5 years old and has been making a few 'worn bearing' type noises, I figure a replacement is in order
Shortly after the machine filled with water, the RCCB tripped again. Got one from AO, delivery tomorrow.