RCD trips randomly !!!!!

Hi All,
Sorry to ask for this issue again. I have the exact same issue. My BG RCD keeps tripping almost once day. It can happens from night to morning. My first thought was the squirrels are invading our loft and is bitting my lighting wires at the loft. I have seen squirrels came out from my loft as a roof tile went missing in April and also heard the scratching sounds from the loft. So I started eliminating the issue. I turned off the heater element MCB, Lighting MCB, Kitchen MCB, garage MCB. Just kept sockets circuit MCB overnight. This morning, I found the MCB tripped but not the RCD. I turned everything back on but nothing trip immediately. I guess it would be either the squirrels bitting my wires or the fridge or freezer are playing up.

I am asking a building to repair the missing tile and arrange a cage to catch the squirrels. My house was built in 80s. My question is would my sockets circuit wires running up to the loft? I thought it would only lighting wires run up to the loft but I am not 100% sure. Any other suggestions would be very helpful.

Cheers

Wongcna

 

It is impossible to diagnose an intermittent RCD fault on a forum. Its hard enough for a spark on site to find the cause let alone prophesize where to start looking. Just get a professional in to take a look.

 

I deal with these kind of faults multiple times a week and they can be a real pain, as all sparks will be well aware of.
I can see why some sparks would remove the RCD altogether, but obviously wouldn't recommend it.
One trick I do use however, certainly with randomly tripping RCD's is to move the suspect circuit to the other side of the board (if the other side is also protected - split load etc). Then, if the other RCD starts to trip randomly, the suspect circuit is confirmed and your efforts can be concentrated there.
Other things to note, and I always ask - is the tripping weather related? Damp in the back of sockets, outdoor sockets, SWA's or other cables feeding sheds/garages etc have all appeared on my list of found faults. I even once found a terminal block (choc block type) buried in a flower bed where someone had dug through a cable and repaired it themselves.
Being strictly 'Emergencies Only', I often follow behind other 'electricians' when they have given up or it's got too late in the evening and they've gone home, and I all too often find they've swapped lives round in the board without swapping their corresponding neutrals. This obviously trips the RCD as soon as the MCB is switched on which seems to make their headscratching even worse!
I do fully agree with Unphased above, it's certainly a job for a professional and not something a homeowner or even inexperienced electrician should be carrying out. There are too many things that could be going on, or that could go unnoticed.

 

Many appliances have input filters on the supply, these contain capacitors and voltage dependant resistors among other items. It is their purpose to shunt any high frequency component present on the 50Hz ac supply, to earth. Now it could be that your input filters on the washing machine, microwave, computer and TV are all working well, but when a high frequency transient comes along, they all shunt it to earth, giving an apparent fault current or imbalance detected by the RCD, which responds by tripping. As you say it trips at night it might be an idea to unplug all equipment from all socket outlets over a couple of nights and see what happens. If you have no tripping, plug half of the stuff back in, if no trip, unplug them and try the other half. Then use the binary split to narrow down the fault.

 

As the above posts have said, its about starting an investigation process that starts broad and narrows the fault bit by bit. First you need to ascertain on which circuit the issue is on, then to further narrow it down to the device or cable, or possibly there is more than one device or cable causing the issue.

I had an RCD tripping issue that occurred out of the blue. Narrowed it down to the circuit, then to some work I had done and found I had crimped a cable so that the insulation on the neutral had been cut into and was earthing against the switch back box.

You may get lucky investigating yourself as I did, or may need to call in a professional who has much more experience in such things and tools too.

 

As an electrician one has to balance time and material costs, as an industrial electrician costing was my problem, so it was a quick look, if not found swap RCD for isolator and all MCB's for RCBO's this does two things, one it keeps all other circuits running and two it shows which circuit has the problem, but at £25 for each RCBO it can be expensive depending on manufacturer. Loosing a machine could cost us £1000 an hour so for an industrial set up RCBO are the cheap option.

Working with just two RCD's the problem of earth - neutral faults taking out the RCD means switching off the MCB often does not work, first is to get the insulation tester out and look for faults, however faults causes by freezers auto defrost are hard to find as once tripped timer goes back to zero, so you switch back on and everything works.

Also not all RCD's are equal, I have some very old ones in my house, mid 90's and every round again I will have a bout of tripping, then with nothing changed they will run another year without problem. Just a spike on the line can trip them some times. I have a new consumer unit ready to change so I can use RCBO's but still on my to do list.

 

For many years my house was fitted with an RCD and it tripped randomly three or four times a week. After my son went to uni we decided to replace the stair carpet leading up to his room. We found, under one of the treads, a 12 volt burglar alarm pressure mat connected to a table lamp in his room that he'd 'wired' into the mains! Removal of mat - 90% reduction in trips!

Five or six years ago we had the house mostly rewired and RCBOs fitted. We've had the kitchen RCBO trip on two occasions since then. Inexplicably the cable to the cooker hood became faulty and replacing it resolved the issue. The second occasion it tripped in the night when the only appliance on was the fridge / freezer.

 

Hi,

I have just moved house and I am getting occasional RCD trips. I am having to use a number of daisy chained extension socket blocks to get mains to areas of the living room, very little are connected to each one and all low current (Alexa, lamp, laptop) and a special mains conditioner to power a hifi system, this has never been an issue before. The rest is standard kitchen built in fridge freezer dish washer washing machine, oven) and a few others.

someone mentioned using a standalone plug in RCD and I wondered could this be a way to track down the possible fault. As it is so random, and not possible to prove a negative i could use it to eliminate the above wiring and point it to one of the built in appliances

I rent the bungalow so I do not want to call the landlord until I have attempted to ensure any of my stuff is not causing it

Jessica

 

If you have just moved in then the landlord must have supplied you with an electrical safety inspection report, an EICR.

So has the installation been checked within the last five years and do you have a copy of the report?

 

Yes I do and attached it, I am not a electrician but am an electronics designer so have some basic idea, however I may have missed something. The RCD has been tested to trip from each circuit and I see there is no leakage live earth but as this is random and occasional could it pass these tests?

 

That makes interesting reading.

On the face of it the report reads as the installation is in tip top condition with excellent insulation test results for all circuits.

Reading between the lines, the sockets are on two 20 amp radial circuits, it would not surprise me if that’s a 32 amp socket ring circuit split into two, because of previous issues.

It is also TT with a single upfront 30 mA RCD, so fault finding will involve everything in the house, all the circuits in the house and all the appliances.

Switching a circuit off at its MCB won’t disconnect the circuit as they are only single pole devices.

Personally I would carry out insulation testing at the consumer unit, then it I find a low insulation test result start disconnecting circuits including their neutrals within the consumer unit to narrow it down.

In theory, given the test results on the EICR, the fault is more than likely with an appliance, but I think the installation insulation test results may need reviewing.

 

Thanks Happy Builder. I will look into it, would PAC testing the appliance be of any help?

jessica

 

It's called a PAT (Portable Appliance Test)

Your HiFi mains conditioner will have filter components which may increase leakage to earth. That coupled with other appliances may cause the RCD to randomly trip. Also, if the RCD has become sensitive thus operating at a lower threshold, it may trip more often.

The appliances would need a PAT and an electrician to test the RCD.

You may wish to consider removing the personal details on the EICR and filename as this is a public forum.

 

Think you need to cover the name of the contractor on the certificate