Cooker tripping CU

[Estrella]

Hi,
A very brief bit of history first.

Buy new cooker 2 years ago and connect. Works perfectly for 18 months then for no obvious reason every time grill is switched on the CU trips. Hob and oven work perfectly as before. Live with this for 3 months assuming cheapo cooker grill is foobarred.

Buy new cooker and as soon as grill is switched on or ovnr temp wound up past 150 degrees it trips the CU.

Common sense tells me that the grill in the cheapo cooker is probably OK after all , and there is a problem with the aged combined cooker isolator switch/13amp plug socket or other fault with the supply or CU. Although why it would work perfectly for over 18months then spit it's dummy I don't know.


Any ideas please fellas?

EDIT: The fuse in the CU never blows, just trips.

 

[JohnD]

I am going to guess that it is an electric cooker, not a gas one, and that it is connected via a large connection block in the wall, not through a plug and socket. And I am going to guess that you mean the RCD trips, not the MCB. And I am going to guess that you have a single 30mA RCD that protects all or many circuits, including the central heating and the sockets, and possibly also the external lighting and the garden socket and your fishpond and your washing machine. I am going to guess that your CU does not have fuses in it, but MCBs.

How many guesses have I got right?

 

[Taylortwocities]

Probably most of them.

Can we have a pic of your consumer unit with a note saying what it is that trips?

 

[Estrella]

Hi John

The CU is pictured below and I hope will help with some of the questions. There is a 30mA fuse for the cooker socket.

You are quite right everything here is electric (no gas). I am also fairly sure that the cooker fuse in the CU only covers the cooker only. The cooker is a free standing cooker/hob combined unit.

You are also correct that it is indeed the RCD that trips.

 

[Estrella]

And one more pic showing more of the CU

 

[Taylortwocities]

So JohnD has identified your basic problem with your installation:

And I am going to guess that you have a single 30mA RCD that protects all or many circuits, including the central heating and the sockets, and possibly also the external lighting and the garden socket and your fishpond and your washing machine.

You need to get that sorted or you will always get random tripping that will plunge the whole house into darkness and (when you are on holiday) defrost all the food in your freezer.

John: fuse carriers, there's a surprise!

 

[JohnD]

OK. You have one 30mA RCD which covers the whole installation. This is undesirable because:

1) it will trip when the total leakage, from all sources within the house, adds upo to (about) 30mA or more

2) when it trips, you lose all power to all circuits, including those that are not faulty, and those which may be required for safety, such as lighting.

I bet your problem is related to (1) above. You probably have, e,g. 10mA leakage from your washing machine, 10mA leakage from your central heating boiler and pumps, 3mA leakage from your kettle, and 6mA leakage from the cooker. The cooker leakage on its own is insignificant and not a problem, but because you have a background leakage in the house fluctuating around 23mA already, the extra leak from the cooker is enough to make the RCD trip.

The best way to deal with it would be to shovel money at a suitably qualified electrician, and have a new CU fitted. Instead of one RCD for the whole house, you can several, each dealing with one or more circuits. if you want a first-class job, you can have a CU fitted an an RCBO for each circuit instead of a fuse or MCB. This includes an individual RCD just for that one circuit. It does work out more expensive though, as RCBOs cost in the region of £30 each

An alternative would be to have a new CU added, and run the cooker off that, with an RCBO for the cooker circuit. In this case it would be an advantage to have a large CU fitted so that any new circuits can be added to that new CU, with an RCBO for each, as and when the need arises. It is useful to have a separate circuit for kitchen sockets, for example.

p.s. 0.03A (on your RCD) is the same as 30mA

Your cooker fuse is 30A which is a lot more.

 

[Estrella]

Thanks TTC.

Unfortunatly I try and assign logic to everything.

I have never ever had random trips. The first and only trips have been with the cooker which was fine for 18months and the previous cooker was fine for 12 months prior to that.

The trips i get aren't random , they happen when the grill is turned on, and don't happen under any other circumstances.

Can you give a reason for trips now and no previously? Just trying to gain some understanding here.

You need to get that sorted

can you be specific please?

 

[JohnD]

(1) above

It is quite usual for cookers to have a bit of earth leakage, especially as they age of if they are damp.

Most earth leakages come from watery appliances though.

 

[Estrella]

OK. You have one 30mA RCD which covers the whole installation. This is undesirable because:

1) it will trip when the total leakage, from all sources within the house, adds upo to (about) 30mA or more

2) when it trips, you lose all power to all circuits, including those that are not faulty, and those which may be required for safety, such as lighting.

I bet your problem is related to (1) above. You probably have, e,g. 10mA leakage from your washing machine, 10mA leakage from your central heating boiler and pumps, 3mA leakage from your kettle, and 6mA leakage from the cooker. The cooker leakage on its own is insignificant and not a problem, but because you have a background leakage in the house fluctuating around 23mA already, the extra leak from the cooker is enough to make the RCD trip.

The best way to deal with it would be to shovel money at a suitably qualified electrician, and have a new CU fitted. Instead of one RCD for the whole house, you can several, each dealing with one or more circuits. if you want a first-class job, you can have a CU fitted an an RCBO for each circuit instead of a fuse or MCB. This includes an individual RCD just for that one circuit. It does work out more expensive though, as RCBOs cost in the region of £30 each

An alternative would be to have a new CU added, and run the cooker off that, with an RCBO for the cooker circuit. In this case it would be an advantage to have a large CU fitted so that any new circuits can be added to that new CU, with an RCBO for each, as and when the need arises. It is useful to have a separate circuit for kitchen sockets, for example.

p.s. 0.03A (on your RCD) is the same as 30mA

Your cooker fuse is 30A which is a lot more.

Thanks John, great info.


Can a higher rated RCD not be fitted to the existing CU ?

 

[JohnD]

it can, provided you don't want to have protection against potentially fatal electric shocks

(i.e. this is not a good idea)

 

[disinfo]

Box,

I see from your other posts you are a computer person.

Class 1 Computer equipment also puts a small current onto the CPC (1-3mA), so if you have a fair amount of IT equipment, it can soon add up.

 

[Estrella]

Hi Dis, Not too much to be honest. 4 lappies and a desktop.

Can I absolutely rule out any other cause? I really don't want to fork out a load of cash just before Christmas if it isn't going to fix the cooker issue

 

[JohnD]

you could try taking out the fuses for all your other circuits, and seeing if the cooker still causes a trip. However this is not a perfect test. But more than likely your problem is due to cumulative earth leakages from multiple circuits. It's very common.

Look on the bright side, if you get your cooker on its own RCBO, at least when it trips, it wil not take the lights and freezer with it

Not all electricians are familiar with RCBOs in domestic installations, as they were mostly used industrially until recently, so mention that you want a new CU for the cooker circuit, with an RCBO and with ample space for future expansion. It is notifiable work so not a DITY job. From your other photos I see you already have an Isolator by the meter, which will make the job a little easier. Your Main Bonding (to gas and water pipes) may need to be bought up to standard though.

 

[Estrella]

Thanks John.

I'll try the fuse 'process of elimination' tomorrow. If nothing else I may find out why it has been fine then started tripping recently.

cheers