Nuisance trippage of main incomer

Mains switches don't as a rule trip, unless it's an upfront RCD for some reason.

Can you post pictures of the mains cable, mains fuse, mains switch and your CU.

Pictures will greatly help it trying to point you in the right direction.

If it’s 100mA upfront rcd, cumulative earth faults might not be the cause unless you’ve got a awful lot of chargers, electronic devices etc…

Did previous electricians check all circuits for possible faults? Outside lights etc?

Looped supply to next door shouldn’t be a problem, being before the rcd

Maybe time for a new distribution board… might not find the fault, but it would affect less circuits.

Change the Cu for a d/p rcbo type.

littlespark said:

If it’s 100mA upfront rcd, cumulative earth faults might not be the cause unless you’ve got a awful lot of chargers, electronic devices etc…

Did previous electricians check all circuits for possible faults? Outside lights etc?

Looped supply to next door shouldn’t be a problem, being before the rcd

Maybe time for a new distribution board… might not find the fault, but it would affect less circuits.

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Hi, there is no power outside of the envelope of the property. Its all internal . It happens so infrequently and randomly that i make a plan to try and focus on it when it happens but then let it slide The most recent incident was when i went away for the weekend. There was nothing in use save for stuff on standby eg the tv and the fridge. It cant be the fridge as it occured with the one before also. My immediate conclusions are that its just an inherent weakness in the wylex main incomer circuit breaker, maybe a mechanical intolerance, or there is a very random micro failure/ micro contact pn the household wiring carcass. I've currently popped the MCBs for the immersion heater circuit and the cooker circuit as they are not in use.

I did note that the cooker switch unit which has a built in three pin outlet, isnt on the ring main . ie when i switched off the cooker supply at the CU mcb, it also killed power to the built in socket on the cooker switch unit in the kitchen. I presume this has some kind of internal fuse to protect the socket as it must be fed internally from the cooker supply ?

As you say though, im wondering what would happen if i had a new CU with one RCD. Maybe if there IS really a micro fault, a single mcb would pop?

As you can see, space is a bit limited for a CU swap as its all in a built in meter box.

Psssst said:

View attachment 98167

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Have the Cu changed, it can only make it better, except for the cost part of it of course.

The unmarked 32 amp mcb which I'm guessing is the ring final has more than one circuit in it, so you could really do with at least an extra way

Ps it's a 30ma rcd

Everything's on a single 30mA RCD, which can trip on as little as 15mA and still be in spec, so not surprising that it occasionally trips.
It might be an earth to neutral fault somewhere, including on the cooker and immersion heater. Switching off the MCBs for these circuits doesn't help for this kind of fault. They must be switched off at their isolators.

The socket on a cooker switch is normal. The fuse is in whatever you plug in.

Your db is old… no getting away from that. Highly likely the rcd has just given up.

Could you measure the width of your board there…. Actually the space that you have?
I reckon a 6 way RCBO board would fit… will be 10 module. 6 outgoing circuits, 2 module mainswitch plus and mcb and SPD.


Just be aware that swapping a board isn’t a DIY project. You need a professional involved and possibly a service isolator fitted by your supplier beforehand.

Even with a perfectly good 30mA RCD, a whole modern house on it is going to cause random trips from time to time just due to the accumulated leakage of everything. As @littlespark says you can probably get a modern board in as you seem to have a bit of space above it.

My own flat had a rewirable board and just enough space to get a Wylex NM606FLEXS on without having to change the backboard area. Size is quoted as:

• Height: 241mm
• Width: 261mm
• Depth: 121mm

I suspect that board has been replaced with a different part though as Wylex now seem to offer the 1-module SPD instead. However, the same principle applies that having an all-RCBO board (each circuit has its own RCD built in to the over-current protection MCB) will either eliminate the problem completely, or at least identify for certain the faulted circuit, and from there if it is cable/accessories, or the appliance.

Cable and accessories would be tested anyway as part of a professional installation so common issues there would be discover at that point, but intermittent faults are much harder to locate as often they simply don't manifest when the electrician is present with IR tester to look. Examples include occasional rain ingress to a junction box below the floor, or things like the defrost heater in a fridge/freezer that kicks in once per fortnight, etc.

You existing board has 6 circuits which ought to be sufficient in any new board, but if space permits then getting a slightly larger board to have a spare slot or two is a very good idea. The cost difference in enclosures is negligible, most extra cost comes from the added RCBOs and circuit testing which would come later, if needed.

Also your 32A breaker for what I guess are your sockets appears to have 3 cables going to it, that can be a bit worrying as normally 32A if for a RFC (ring final circuit) where you would expect 2, the 3rd might be a single socket/pair which is OK, or it could be a radial with several sockets in which case they ought to go on a separate 20A breaker.

Psssst said:

As you say though, im wondering what would happen if i had a new CU with one RCD. Maybe if there IS really a micro fault, a single mcb would pop?

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@pc1966 addresses this, but to be clear: a modern CU would have a 15-20ma fault tolerance for each circuit, rather than 15-20ma fault tolerance for the whole house. If there is a large issue on any one circuit you would then find out which one it is, and that is a great head-start in solving the problem. Well worth a CU swap in my opinion.
(There are several forum members in Manchester if you wanted a estimate.)

Hi all ,
Thanks for all your advice. I'm not looking to do any DIY on this as of course i realise its a job for a qualified electrician and that its part P work etc.

I had a more detailed look and the existing unit is 345mm (wide) x 210mm (high) . As you can see from the pics its tucked at the bottom of the cupboard and there's at least the same space of baseboard again above it. At the top is the meter which is rotated and faces outward so that it can be read from outside via a lockable hatch. The supply fuse is on the right and still has its seal intact i think.

The line up on the mini breakers from L>R reads
Lights
Lights
Heating (central heating circuit- for gas boiler and controls etc)
Water heater (immersion- popped out as not used any more though the immersion is still in place, wired in-has isolator in cylinder cupboard)
Power ring main ? ( Wylex B32) so it looks like there is only one power outlet ringmain for the whole house?
Cooker

The extra wire in (B32) is a single socket wired off it.

All the wiring enters via the rear of the unit. As the white meterbox is inset into the inner leaf of the wall, it appears that all the wiring is via the cavity.

There is no supply isolator. I had a look on Electricity NW website and found a doc which said it wasnt their policy to fit isolators and then stuff about a de-energise/re-energise service.

I didnt know what the forum rules/ etiquette were re quotes , if its allowed i guess anyone could message me? Its in ceentral stockport

ive added a few more snaps and i guess thats about it for now until i progress the job. Thaanks all.

A fusebox make 11 way would fit

Dimensions of F2011M are - H263 W306 D116 (mm)

timhoward said:

@pc1966 addresses this, but to be clear: a modern CU would have a 15-20ma fault tolerance for each circuit, rather than 15-20ma fault tolerance for the whole house. If there is a large issue on any one circuit you would then find out which one it is, and that is a great head-start in solving the problem. Well worth a CU swap in my opinion.
(There are several forum members in Manchester if you wanted a estimate.)

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That would only be entirely true as long as D/P rcbos are being used of course.