RCCB issues

[Stevie Brim]

We are having problems with nuisance RCCB trips. When it trips, we re-set and appears ok for a while (maybe hours) then trips again.

We’ve tried to isolate the issue but can’t seem to track down the problem. I would like to understand some basics about our consumer unit to see if I am doing the right things. We didn’t install it so would like to confirm my understanding.
I’ve attached some images of the consumer unit. I believe the RCCB protects everything except the lights. There are 5 switches (MCBs?). There are marked and I understand they are for the following;
1. Garage - seperate garage. Cable is underground. We have an overflow fridge freezer and outside spot light plugged in there. I isolated this area before and still had tripping issues. We’re using the freezer currently as the other one needs replacing (see below).
2. Oven/Hob - to one socket which has plugs for gas hob ignition and electric oven. The oven only requires 13 amp plug into a standard socket. This is currently switched off.
3. Shower - I believe this is redundant as we have don’t have an electric shower but one that works off a direct hot water feed from the combi boiler. I’ve currently switched this off.
4. Cooker Hood and Wall fan in kitchen. This is currently switched off.
5. All Sockets upstairs and downstairs

As you can see, there are 2 switches (MCBs?) for the lights, one for upstairs and one for downstairs.

None of the MCBs have ever tripped. The RCCB trips and everything goes off except the lights.

My initial questions are as follows;
a. If I switch off any of the 5 switches then that circuit is completely isolated and if a trip occurs then appliances on that circuit cannot be causing it?
b. Are there any circumstances at all when the light circuits can cause the RCCB to trip even if they are not protected by it? We can find no evidence of water getting into light fittings or light switches but we have had the lights flickering.
c. The boiler does not have a plug as it’s hard wired into a fused switch which is connected to the sockets circuit. This is a new boiler fitted about two months ago and despite the fact that it has worked ok I want to isolate it. Am I able to isolate the boiler by switching it off or should I also remove the fuse from the switch?
d. There is also a fused switch to which is connected an under unit strip light. Can I isolate this by switching off or do I need to remove the fuse as well?
e. We have an extractor fan in the bathroom linked to the light switch. It has a delayed switch off. I think it’s connected to the sockets circuit somehow. How do I isolate this?

During our investigations we’ve had the dishwasher and fridge freezer checked out under insurance as I noticed the wire/plug was getting hot on the dishwasher and fridge was freezing up with the thermostat set to low. We were told both needed replacing so we have switched off and unplugged both. Despite this, we are still getting trips.

Also during our investigations we noticed a minor leak from the shower tap which looked like it might also have been leaking behind the tiles. Plumber came and tightened the valve. However, we have never see any water coming down into the kitchen below either down walls, through the ceiling or into a light fitting (however I would like to understand whether water in a light fitting would trip the RCD hence my question above). Plumber said the leak was unlikely to be causing the trips.

During the last 2 weeks we’ve thought we’d isolated the problem only for it to start again. My wife came home yesterday after nearly 2 days without a trip. Ran a bath for my granddaughter. RCD tripped twice in 20 minutes at about 6pm. Didn’t happen again until about 3am (I know this because I suffer a sleep disorder so use a powered machine to help me breathe which stopped), then again just under an hour later and once more at about 5am.

At 5am I switched the power to the boiler off. Turned it back on about an hour ago. Boiler has been working and heating up the house in the last hour. No tripping....

We spoke to one electrician a week or so ago who said it was pointless coming until we’d identified where the problem was. We’ll get someone in to check the boiler electrics first under the warranty despite the fact it appeared to be all working ok up to a couple of weeks ago and has been ok in the last hour.

I know that problems with multiple appliances could cause tripping so this could be a slow process of elimination in switching equipment off and seeing what happens but if someone can respond to my questions on isolation and how the lights might have a bearing on what’s going on, this would help.

I’m not much of a diy man so I’d be very grateful if you could avoid too much technical jargon in your responses.

Thank you

 

[crystal ball]

When I am investigating random tripping I always look at possible water related problems first, leaky pipes, outdoor kit, etc, also be aware that isolating a circuit using the MCB leaves the neutral connected, a neutral - earth short will trip the RCD

 

[bernardgreen]

If I switch off any of the 5 switches then that circuit is completely isolated and if a trip occurs then appliances on that circuit cannot be causing it?

Incorrect, the MCB ( switch ) only disconnects the Live of that circuit, the Neutral is still connected, A Neutral to Earth fault on a circuit can trip the RCCD when the Live to that circuit is isolated.

 

[Taylortwocities]

As Bernard has pointed out, Isolated means disconnecting the LINE and NEUTRAL connections. Just turning off the MCB will not isolate teh circuit.

To do it, you are going to have to get inside that consumer unit and start removing cables.
Or get an electrician with an Insulation Resistance Tester to identify the fault for you.

 

[Stevie Brim]

Thanks for your post
I think I might have been looking in the wrong place all of this time! During the bad weather we had some snow on the roof and a leak when it thawed. Normally the roof doesn't leak so I shut everything off in there at the time, waited for the snow to melt and everything to dry. Switched it back on and there appeared to be no problems when we were away for a week.
When the tripping started I shut off the MCB for the garage assuming (incorrectly) that it was isolated completely. There is an very old large switch in the corner of the garage which has got a switch with a window showing the words ON in Red and probably OFF in Green. I've never touched this. The underground cable goes into the bottom of this and the cables to the lights and sockets come out of the top, up the wall and across to the sockets and a few feet across the roof beams to the light fittings. If I switch this old switch off will it isolate the cables, sockets and light fittings in the garage? From your information, I assume the old switch box itself will not be isolated and could have a "neutral to earth" fault but at least if I can isolate to the cabling in the garage beyond the switch and that would help me track down the issue?

 

[bernardgreen]

Finding Neutral to Earth faults does require the electrician to disconnect the Neutrals inside the consumer unit before doing the testing.

A Neutral to Earth fault on a circuit with the Live switched OFF may not cause the RCD to trip until a load on a different circuit is switched on. This can mislead people ( including some "electricians )as to where the fault is.

For example the RCD trips when a kettle or toaster on the kitchen socket circuit is switched on. This suggests that there is a fault on that socket circuit when the fault is actually a fault on another, possibly isolated for testing, circuit.

This might help to explain why this happens. ( click on the image to enlarge it )

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

 

[John D v2.0]

I suffer a sleep disorder so use a powered machine to help me breathe which stopped

Depending how important the machine is, it may be worth getting a specific socket on its own RCBO fitted. This means it would stay on regardless of what happens in other parts of the installation, unless the main power was lost or there was a fault on that circuit.

 

[winston1]

During our investigations we’ve had the dishwasher and fridge freezer checked out under insurance as I noticed the wire/plug was getting hot on the dishwasher and fridge was freezing up with the thermostat set to low. We were told both needed replacing so we have switched off and unplugged both. Despite this, we are still getting trips.

As an aside I don't believe either need replacing. A dishwasher plug, or rather the 13a fuse inside it, will get hot as a dishwasher when heating water is a large load. If you replace it the new one will be the same.
Regarding the fridge, all that needs replacing is the thermostat, or possibly the defrost heater if it is an automatic defrost type. Either much cheaper than a new fridge.

 

[Stevie Brim]

Thank you Bernard for your comments which have been really helpful. Just to clarify, if I shut off this old style large switch situated in the garage, will that shut off the electricity to everything in there? Sorry, but I'm still struggling to understand why it wouldn't do this. I appreciate it could unearth other problems but as I believe we the snow melting into the garage might have created a place for rain now to get in, just eliminating shutting down the garage from that old swtich may help?

 

[Stevie Brim]

Hi John D. Thanks for your response on the machine. It's not life threatening so what you suggest is not really required.

 

[bernardgreen]

if I shut off this old style large switch situated in the garage,

It might disconnect both Live and Neutral but without seeing it it is impossible to tell, and even then it might be necessary to see the inside of the switch before being able to give a definate answer.

 

[JohnW2]

Just to clarify, if I shut off this old style large switch situated in the garage, will that shut off the electricity to everything in there?

Quite possibly, but not certainly. A photo might help us to improve that 'guess'.

Sorry, but I'm still struggling to understand why it wouldn't do this.

It just depends upon whether, when switched off, it disconnects both Live/Line and Neutral, or only the former. Either is possible.

I appreciate it could unearth other problems but as I believe we the snow melting into the garage might have created a place for rain now to get in, just eliminating shutting down the garage from that old switch may help?

Well, even without/before being certain whether that switch produces 'full' (i.e. L and N) isolation, there's no harm in trying. If switching it off makes the trips stop, then that would tell you a lot.

Kind Regards, John
Edit: I'm typing too slowly again!

 

[Stevie Brim]

Thanks Winston1. The guy who came to look at both said that the insulation in the fridge had broken down so it was unrepairable and that the seal in the dishwasher was letting water leak below the washing compartment. In both cases, the replacements were paid for by insurance except a small delivery charge. Both were quite old and were in-situ when we bought the house 4 years ago. I know having insurance doesn't pay but as they were already quite old when we bought the house, we decided to cover them.

 

[John D v2.0]

We spoke to one electrician a week or so ago who said it was pointless coming until we’d identified where the problem was.

Not necessarily quite true depending on budget.
They could change over all the MCBs to rcbos which would narrow down which circuit had the problem and also remove the possibly of losing power to the rest.
However that would cost a bit even assuming they're available for your unit.

 

[Taylortwocities]

just eliminating shutting down the garage from that old swtich may help?

It may isolate the garage wiring. Give it a go, it’s only a switch it may help narrow down the location of the fault.