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Power Spikes/ Tripping C50 30mA RCBO

DRD

DRD

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Any help gratefully received here.

My kitchen is in an extension powered by a separate 50A RCBO out of the main fuse board. It has been blighted by random power trips for about 8 years.

This main RCBO supplies a slave fuse board located in the kitchen. This second fuse board has MCBs protecting the various items in the kitchen. It covers 2x dbl ovens, 13a microwave, 13a steam oven, induction hob, full height fridge and freezer, 13a boiler tap.

The tripping can happen overnight when nothing is being used (I blame power spikes and power cuts for this).

The MCBs in the slave board never trip. It is always the 50a RCBO that fails, taking down the entire kitchen.

But it also happens randomly. It might be just the microwave that does it, or just the grill on one oven, or when we have 4 ovens going. There is no pattern that I can discern.

Months go by with no problems, then a single grill trips it Four times in a row. Move to the other oven and try the grill there and it worked fine.

Does anyone know what is going on here please? Is there a cure ? Do I simply have too many items on a single cable from my main fuse board ? Is there cross talk between the appliances ?

20240508_090523.jpg
 
Earth leakage. I had horrendous problems with this in my house. removed the master RCBO and replaced with an ordinary switch (just so I can still manually isolate & it was easier to swap a switch in than reroute the wires) then replaced the MCB's with individual RCBO's and that solved it.
 
Thanks @AlanJ My main fuse board has RCBOs for every circuit in the house. My electrician insisted on a RCBO at the main fuse box end as the wire across the house to the Kitchen's slave fuse board could be eaten by mice.

This suggests I might need to bite the bullet and put an armoured cable from the main fuse box to the kitchen, relying on RCBOs in the slave fuse box to protect the kitchen items
 
DRD said:
Thanks @AlanJ My main fuse board has RCBOs for every circuit in the house. My electrician insisted on a RCBO at the main fuse box end as the wire across the house to the Kitchen's slave fuse board could be eaten by mice.

This suggests I might need to bite the bullet and put an armoured cable from the main fuse box to the kitchen, relying on RCBOs in the slave fuse box to protect the kitchen items
Click to expand...
Aha yes - mine is armoured to the pin room. the main issue for me was with the split circuit for the main house in the main fusebox, it was always one side that was tripping, so I did the above to sort it.
 
It's a Wylex fuse board that is giving me the grief
 
Overloading the circuit is easy enough to do if you think it's that... Just switch everything on...!

Microwave (high power), hot water heaters, kettles, ovens, etc. It should be easily repeatable. It depends on how you're configured but I would work on a typical 4Kw to trip - so 1kw kettle, 800W microwave would be 1.8kw of your 4kw available. That said, ovens should be on their own independent circuit.

Regarding random trippings, I once had a problem with the central heating pump intermittently tripping the circuit when it tried starting up, My house use to eat heating pumps for breakfast, well wear them out, on a regular basis. I switched to a Wilo glandless circulator and have never had any problems since.
 
Is the cable between the kitchen fusebox and main fusebox large enough.

I remember someone mentioning a while ago about their pin shed doing the same thing randomly and it was down to voltage drop across the cable when they turned something on.

They upgraded the cable to a thicker one and the issue went away.
 
Thanks for all the responses.

Originally this main cable also supplied my pinshed too. I thought all the trips were caused by the pinball machines (11 to 14 of them). So I had a dedicated supply introduced for the pinshed only.

There is some weird **** that goes on when you have multiple devices on a single circuit. It might be 5 light bulbs on one switch. Or my kitchen mess.

It's totally random. On Saturday a single grill was tripping again and again. No other circuits were on.

That same grill has worked every day since.

I think the only solution is to insert an armoured cable with a regular mcb on the supply end
 
I have been a sparky since 1985 and I have seen so many different faults that cause RCDs to trip.

Even have slight damp in the back of the socket/switch boxes.

Once had a socket that someone had 3 x 2.5mm twin and earths in and it was the pressure of the cables being squashed.

THE MOST COMMON thing to cause an RCD to trip is anything with a heating element. Cookers/toasters/ovens/shows/heaters.......

Over time heating elements can fail and slightly go to ground.

Another thing to add is if they trip at 30ma - everything can add together - say the oven has a 10ma fault, the cooker has a 15ma fault, and then the toaster has a 10ma fault - then it goes over that....

What I would advise is change the kitcen board with seperate rcbos at 30ma.

But I would put my money on either damp or a faulty appliance.

Depends if you want a sparky to spend anything between 1 hour and 3 days to find the fault.

Now if your sparky has put an rcbo on an internal cable that is hidden in trunking or under floorboards then I do not think I would of put an RCBO to protect that cable. There is no need. I have only seen maybe 10 damaged by rodent cables in my life and those are little nicks where the mouse goes thru a live cable and its dead. You could also try a 100ma trip I suppose. Armoured cable is excessive within a house and expensive (for a 50amp supply I would want to use 16mm cable).

10mm cable is only suitable for 45amps.

Screenshot 2024-05-09 at 22.40.02.png

Also with twin and earth you need to run it with an additional 10mm CPC (earth). The earth cable in twin and earth is smaller than the main conductors.

You could find a sparky who has the proper test equipment and they should be able to check your appliances for earth leakage.
 
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@Pick Holder thanks for the info.

With my situation, isn't armoured the best bet ?

I have armoured cables from the fuse board protected by rcds to my garage slave fuse board and pinball shed slave fuse board. These give no trouble.

The new cable would pass from main fuse board in the messy pantry. Up wall into upstairs walk in cupboard vertically above which has trunking in it anyway. Along loft to other end of the house. Down via a built in bedroom cupboard vertically above the kitchen slave fuse board.

The only mess is when it hits the kitchen as there is a few feet of wall we would have to channel it into.

Getting pretty sick of this problem as you can imagine
 
Technically, it's classed as a distribution cable and doesn't require any RCD protection on it, that's only a requirement for the final circuits. Replace it with a standard breaker. ( assuming you are on a standard supply type here, not TT ).

I would however, check the leakage using a clip on ammeter and determine which appliance is probably the cause of the fault.
 
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@ian866

what's the test for leakage pls ? What's a decent clip on ammeter to buy ?

Thanks for your wisdom
 
There are lots of clip on ammeters that would suffice, it's down to budget how much you want to invest. Have a look at Kewtech for cheap good value meters : -


Personally, I would look at this being ( as others have said ) a cumulative leakage issue, so I'd be exploring replacing the MCB's with RCBO's and losing the RCD from the feed. I doubt you'd run into disconnection time issues as it is a distribution circuit.

That said, RCD's do get over sensitive and trip for no obvious reason so the one you are having the issue with could just be doing that, replacing it could solve it ??

I'm not advocating you do this, but so long as you are sensible, move the earth out of the way in the remote CU and clip the ammeter on to it, switch each final circuit on and see what you get, if it's over 20mA total that's likely to be your problem. Turn it off at the main feed whilst you are accessing the earth in the remote CU, don't want any accidents :cool: It is possible to do all this using the main earthing connection and not going into anything, but you'd have to turn the rest of the house off. This is where the meter is located. However, you'll get better results conducting the tests at the 'kitchen' CU and using that earth connection as the current is so low.

Splitting them up and using separate RCBO's will solve it. If you are still feeling the need to use an RCD on the feed to it, change that to one at 100mA rating to discriminate.
 
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