intermittent RCD tripping advice please

You seem to have a pretty good handle on the situation.

A clamp meter should work - but you will need one that reads down to a few mA fairly accurately - many ordinary (i.e. cheap) ones don't. The only  drawback of that approach is that a decent amount of leakage has to be present while you're using the meter - which isn't always the case with intermittent problems.

A N-PE fault sounds quite likely - it can be anywhere (even inside an appliance) and can sometimes be present even when the appliance is switched off (if the switching is the usual single pole)  - but only makes the RCD trip when the voltage on N rises - usually due to voltage drop - i.e. when other appliances are drawing current. The difficulty can be compounded by appliances that have some sort of automatic control - i.e. anything from washing machines which switch different bits on an off and the program progresses or heating systems under thermostatic controls.

If it we me I'd go down the IR route and track down the N-PE issue for starters  - a single fault affecting several circuits isn't unknown - often cables run together from the consumer unit and through a common hole/notch in joists so a single mis-placed nail can easily pierce several cables.

If it is just cumulative leakage currents (Air Con might be a good suspect for that too) - there might be some possibility of re-arranging circuits between the two RCCBs to balance things a bit better (but keep an eye on overall loads of each, especially if the RCDs are rated <100A).

   - Andy.

As above.

These things can be a real time consumer.

An L-N test on  meter that can see less than 10mA is very useful.

Poor IR is interesting but assuming the house is wired in plastic cables and not troubled by vermin or flooding, most likely an appliance plugged in rather than the wiring itself, unless there have been building works recently that may have filled a backbox with paint or cement or something else partly conducting.

In terms of loads, things where water is possible are good things to try - the heating pump,washing machines, kettles sheds and outside lights and so on are all good candidates for water in the works type problems.

A real NE short you can find with the power off with any old meter that can do ohms - an insulation test at 500VDC looking for megohms is nice but nails in cables and so on can be found with almost any test set with a little patience even a battery and bell set...

I'm not sure how well the various circuits are shared across the two RCDs or how much slack there is in the box. A cheap but slow alternative is to swap one pair of circuits between the two RCD domains and see if the fault moves over or not. But if it is a cumulative current problem this may not reveal as much as hoped. Perhaps one of the two suspected rings..

IF there are loads you do not need at night - cooker, water heater etc. you could try turning them off at the breaker and seeing if it never trips at night. Again, only a partial diagnostic but it sounds like it is already just knife edge marginal.

Mike.

Thank you both very much for your replies.

What do you think of this meter?

https://www.amecal.com/product-page/mini-ac-leakage-current-tester-st-9810

It has 100µA (0.1A) resolution, which I believe should be good enough for this task? The jaws aren't huge, but maybe that's a good thing for the scope of the testing here? Should I get it calibrated?

I will be going down there after half term to do the testing, so I will report back once I'm there.

My plan will be this:

- Test the whirlpool bath

- Test the heating pump, washing machines, kettle and outside lights

- Test all the appliances on the three ring mains, but focus on the "bottom two" tripping side first

For outside soffit lighting (e.g. LED down lighters) or anything that doesn't have any earth, should these devices be tested?

Thanks again,
Richard

100uA is 0.1mA, not 0.1A, (!) but that is the last flickering digit of the fruit machine, not the accuracy. You need to be able to see changes at the 10mA level, I 'd expect that sort of thing to do it.

I've not used one of those model but I have something like it by Dilog that was really useful for about the first  year, and is now on the 'repair me' pile, as something seems to have failed internally.

Unless it is avery cheap extra I'd be minded not bother with the cal cert personally, as you are really interested in trends of rising or falling as things are added or removed, not so much the absolute numbers.  I have a short extension lead I use where the outer jacket of the cable is removed to expose the brown blue grellow cores for a 6 inches or so  for just this sort of electron hunt for suspect appliances.

Not having a CPC does not mean that there is never another  path to earth - if you put L and N thorough the core side by side you will (to a pretty good approximation), see the difference, much as the RCD does, and if what comes back does not equal what went out, then the difference  has presumably got on or off on the way round ... TVs can lose current down the antenna cables, computers used to lose current down the phone lines before WiFi, and all sorts of funniness.

Be aware that you can have current flowing in your earthed services that is not from your own L-N loop - there is another post today about diverted neutrals I suggest you read the 1st PDF if yo are not aleady up to speed with the idea. Combined with an NE fault this can make your RCD trip or not based on the neighbours loads.

If this is the case, then reading currents in the grelow wire may not indicate a fault that an RCD would see, but the L-N test will.

Mike.

Hi Mike

Yes, sorry, I did mean mA not A! User error.

Ah, the old 'repair pile'... I wouldn't hold out too much hope for the meter lasting many years, but if it helps us find the fault then it will have paid for itself.

I figured the cal cert would probably be for certification etc., so that will help to save on the cost - thanks for that.

Will be using the extension lead solution as you describe for the appliances.

OK, I really wasn't sure about a missing CPC - makes sense though about an alternative path. I knew about the TVs (have also seen some posts on this), but, ah yes, I'm old enough to remember modems and I can see how that could happen too!

I'll check out the diverted neutrals post too.

Thanks again
Richard

Hi Richard,

Would you able to post some clear pictures of all three ring mains ?

There are couple of possibilities of RCD/RRCB tripping

1) Faulty equipment

Solution: Remove all the equipment from the wall sockets or any other electrical/electronic devices and then check if its keep tripping or stop tripping

2) The socket its self is an electrical accessory, some time the twin /single socket creates a fault itself due to ageing or usage

Solution : Its tiresome lengthy exercise but its worthwhile to check each socket by removing it completely

3) R1+R2 reading + Insulation resistance test for troubleshooting the exact location of the fault

Solution : I suggest to do R1 + R2 test on ring mains , if the reading is satisfactory then carry on insulation test, if the insulation test is fail then divide the circuit and do the insulation test from consumer unit to first socket/accessory point and from the first point to second socket/accessory point and carry on until it reach the last socket / accessory point to consumer unit. This will definitely reveal the fault with in the piece of a circuit.

If the initial R1+R2 test fail then you can also find the exact location of the fault by adopting the same method I have explain above.

Any question please reply me I will try my best to see how I will help you.

Kindest regards,

Syed Rizwi MSc CMgr ICT Tech MIET MCMI

if the insulation test is fail then divide the circuit and do the insulation test from consumer unit to first socket/accessory point and from the first point to second socket/accessory point and carry on until it reach the last socket / accessory point to consumer unit. This will definitely reveal the fault with in the piece of a circuit.

It's usually more efficient to divide the ring in half - so test between the consumer unit and a socket near the mid-point - you can then eliminate half the ring in one go. Then divide the faulty section in two, and so on. A binary chop rather than a linear search as it were.

   - Andy.

Just posting at the bottom.

R.C.B.Os rule O.K.

10 final circuits running through just one R.C.D. is a bonkers arrangement/

Z.

Yes that's right Andy, its depends on if somebody lucky find the set of sockets creating half of the ring, sometime even we cannot find all sockets on the particular ring because of furniture and other limitation for example socket hidden behind the kitchen cabinet

Hello everyone again,

We're down at my parents this weekend, so have had some time to do a bit of testing.

I've tested everything plugged into the sockets on the downstairs and upstairs ring main and nothing stood out: zero to 0.1ma readings generally.

I tested the washing machine, dryer, dishwasher, microwave, bath and there is some standing leakage on each ranging between 1ma - 4.3ma. The bath FCU seems to be the highest at ~4.3ma, the other appliances were averaging about 1ma.

Stand alone fridge and freezer in the garage were both zero. Open the doors to get the motors to run and didn't notice any change.

The awning registered 0.1ma on standby.

I tested two air conditioning FCUs upstairs out of curiosity and they both reported 3.1ma in standby. There are five a/c units in the whole house. I was surprised at how high these seemed, but maybe this is 'normal'. Four of the a/c units are on the top CU row.

I've learned that the outside lights were apparently disconnected by the first electrician and the fault still happened, so I haven't checked them.

The kettle, oven and microwave were all isolated a few weeks back and the fault still occurred.

There are a few things in an airing cupboard downstairs (alarm, door phone, motorized value/underfloor heating) which I haven't been able to access enough to investigate/test - I'm also not sure if it comes of the upstairs ring.

I haven't tested any of the down-lighters.

What I have discovered though is that I can now easily and consistently trip the bottom RCBO when I switch on and off an outside light switch or the internal airing cupboard light several times - both are fluorescent energy saving type lights.

Following on from this, in the garage there is a single fluorescent strip light. It is on a circuit on the top row of the CU (i.e. the one that doesn't trip). If I switch that on and off a few times it will trip the bottom RCBO.

Does the ability to get the RCBO to trip aid in anyway with the ability to isolate/locate the fault further or shed any potential light on the problem?

I'm not really sure what to look at next?

Thanks again,
Richard