RCD Tripping Hell with high load

[Richard Burns]

Because you have had electricians working there at least one of them should have tested the RCD to see if it functions properly, even though they may not have done a ramp test as it is not required, this testing should have eliminated the RCD failing as a problem.
Because you have had the 24 hour supply RCD trip when the off peak heating on the off peak supply has come on this means that the fault is reduced to a supply issue or a neutral earth fault because the off peak heating should normally be unable to cause the main board RCD to trip.
If the supply does have a loose connection providing an irregular and highly variable waveform to the main board it is possible but not common for the RCD to be affected by the intermittent effect and trip, this could be initially checked, not by touch!, by observation of the supply tails at the meter and any joints before the meter. If there is a bad loose connection the tails would be getting hot and look darker than normal, possibly signs of flashes if it is dark and a high load is taken. If this is the case then it would need a rapid response to resolve the issue.
If it is a neutral earth fault of high resistance then individual Insulation Resistance
testing of the circuits on the main board should highlight the potential problem, though it would also be critical that the earth was still connected to the earthing system to check for faults to an unexpected earthed part.

The rest of the advice already given above stands.
I would be heading for the NE fault area as a cause based on what you have described.
However only personal inspection and testing would be able to identify it accurately and it may well take a long time. An electrician could also possibly suggest some narrowing down methods if the fault is not clear cut.

 

[Strima]

I would be leaning towards a NE fault. Had one a few years ago where the neutral insulation on a socket outlet had been scored when stripped back on original installation in the 70's. Circuit tested out fine, over 2 Mohms, but when any sort of load was applied the RCD would bang out.

Rather than IR test I ended up doing a continuity check along the RFC to track down the fault, saved me splitting the circuit to narrow down the fault.

 

[telectrix]

as strima. possible N-E fault. shows up when loads applied even to different circuits.

 

[marconi]

Fletch - Could you load up some more images as in (your post #1) which show:

a. to the right of the white MEM box;

b. what is behind the lowered lid of the left hand Wylex CU;

c. the routes of the green/yellow conductors and any bare metal terminals they connect to;

d. the routes of the thick grey conductors.

e. the clamp for the water bond.

f. your intake and meter.

Top left in the white conduit - are they thick round grey conductors or thinner flat ones?

 

[Fletch]

were away from the house now, with the whole thing and a 10 week old we've decided to shift out as it's getting a little over complicated to deal with. So I can do my best to describe but no pictures.

a. to the right of the white MEM box; is a standard 100 am electrical board fuse, one with the "do not touch ownership of welsh electric board, criminal offence" hazard on it.

b. what is behind the lowered lid of the left hand Wylex CU; nothing but wall, as far as I know. Just the feed from the MEM switch into the CUs

c. the routes of the green/yellow conductors and any bare metal terminals they connect to; yes, there's a metal "terminal" rail style thing with about 10 holes and 10 grub screws that then connect to the earth cable that goes out to the new earth rod outside.

d. the routes of the thick grey conductors... by conductors I guess you mean wires? They come in through the wall, into aforementioned 100a welsh board fuse, into the Meter, into MEM Swicth in to CUs

e. the clamp for the water bond. : there are technically 2, on under the sink attached to mains pipe (install during electrical safety test) and one I attached to the piping in the old immersion cupboard this weekend. Though it still tripped before I did that. Both are silvery metal screw clamps.

f. your intake and meter. : The big grey box in the picture is the meter.. the "intake" in gather you mean the mains cable into the property. Comes from next door under guttering round house and in via hole in the door frame in kitchen.

Top left in the white conduit - are they thick round grey conductors or thinner flat ones? That conduit contains all 3 core 2.5mm wires.

Will post pics as soon as I can!

 

[David M]

as strima. possible N-E fault. shows up when loads applied even to different circuits.

This thread reminds me of a RCD intermitting trip fault I attended to a few years back. After an extensive inspection and test of the installation the problem turned out to be an extension lead that was plugged into a socket outlet supplying a bed side alarm clock. The extension lead had been incorrectly wired - N&E reversed. The alarm clock functioned and the earth "leakage" on its own was not sufficient enough to cause the RCD to trip. As soon as a few extra loads where added at the same time, i.e cooker, kettle, immersion, lights... the RCD would trip.

 

[marconi]

Fletch, could you answer these questions please?

1. You state that the 24 hr rcd does not trip when a single large load is turned on eg: immersion heater. Does the rcd remain closed when only the immersion heater is on and its thermostat reaches its set temperature.

2. And is it also so for the heater alone?

3. Does the rcd remain closed when say the oven is first turned on to 220C say and an electric ring is turned on at the same time to low heat setting? Or trip after a few minutes?

4. Does the rcd remain closed when a cold oven is first turned on to 100C and an electric ring is turned on at the same time to the highest setting? Or trip after a few minutes?

5. If you turn on all the rings and oven of the cooker what happens?

6. You state the rcd will trip if the heater is on and the hoover is then turned on. What happens if only the the hoover is turned on and after 20 seconds turned off?

7. What happens if you turn the hoover on and then turn on the heater? And then turn the heater off?

8. If you have a washing machine, tumble dryer or microwave could you un-plug them all and then turn on some items you know usually cause the rcd to trip immediately. Any difference?

9. Do you have an filter socket outlets. Folk sometimes have them as 4 way socket strips and they are marked up as such. If you do unplug it and repeat 8.

10. In general would you say the tripping always occurs when the loading is high and another high amperage load is switched on? Or is 'always' more like 'often'?

OR

11. In general tripping occurs when the loading is high and a high amperage load is switched off by its internal thermostat. Again 'always' or 'often'?

Enough questions for now - I am off for a swim.

(None of these questions replace the requirement for the tests and inspections mentioned in previous posts. But the responses may help understand better what and where the problem is.)

 

[marconi]

Fletch - last from me for today: Please contact your Distribution Network Operator(DNO) which is the company you would call if you had a power cut and ask them if it is possible to convert your home's supply from 'TT' to 'TNCS' and ask how much they charge. Don't commit to doing it just yet - I just want to know if it an option for you.

 

[ringer]

This won't help the OP with his problem, but what worries me is that he says the RCD had been bypassed. It is an RCD mainswitch - how exactly had it been bypassed?!?!?!

 

[Generator]

In all this testing, retesting, checking etc, etc, everyone seems to be assuming that the RCD in question cannot be at fault! Testing it with a 30mA test leakage current does not guarantee it won't spuriously trip when a large load is suddenly switched on.
The easiest way to eliminate that would be to change it! - they aren't that expensive.
If the RCD is faulty at high loads, no amount of other testing will solve it.
Always try the easy things first!

 

[marconi]

This won't help the OP with his problem, but what worries me is that he says the RCD had been bypassed. It is an RCD mainswitch - how exactly had it been bypassed?!?!?!

On 24hr board - RCD bypassed by Lin to Lout and Nin to Nout and relying on the white MEM DP switch as single means of isolation perhaps? (see #35 paras b and d)

Eco7 Board may be similarly bypassed - we are not told.

What 'this'?

 

[davemoorenipper]

Fletch, are you sorted yet?

I commute to Abersoch bi-weekly and could inspect/resolve if you wish.
PM me with your details if you wish top rogues this.
Regards
Dave Moore

 

[davemoorenipper]

Should have read 'to progress this'
D

 

[MJPD29]

It sounds like you have an earth leakage issue possibly if it is only when it is under load?

 

[FUSEServices]

Did you ever resolve this? My best guess is a loose N conductor in the meter / cutout, if everything else is ok.

Some people also presume they can test an appliance at the plug, but I'm sorry, a cooker, washing machine, dishwasher etc, have heating elements and motors that are only energised through a relay when the machine is operating. The ONLY way is for a clamp meter on the earth to measure earth leakage when these appliances are cycling through their operations.

I once had a dishwasher causing the RCD to trip. It was a break in the cable linking the door to the main body (I presume) as we managed to find it tripped in a certain position.

Love to take on your job but too far for me and you MUST have had it sorted by now. RCBO board would certainly help with this.

Also - final thought. You could have a shared / borrowed Neutral. You say you had an electrical test, but whoever did it failed to note the alien MCB in there, so I doubt he has done a thorough job. Has anyone undertook continuity / insulation resistance between all the neutrals? It's seldom done but very important.