Bosch oven/grill is tripping the electrics

Second issue with our bungalow.

Been living here for almost 3wks. The electric Bosch oven has been working fine. Two days ago, we went to use the grill but it tripped the RCD. The grill would turn on fine but would trip when it was turned up. Tried it a couple of times and it kept tripping the entire RCD. In view of this, we did not try again.

Yesterday (the first time since the grill issue) we turned the oven on. It turned on fine but when you turn the temperature up, it caused the entire RCD to trip. We tried it a few times but it it kept tripping.

Any ideas? Is it likely to need new elements? I dont wanna splash out on two new elements (oven and grill) if the problem is elsewhere.

Many thanks.

Faulty element(s) is very likely, there isn't much else in an oven to go wrong.

It sounds like you have one RCD protecting all or several circuits. This is poor practice. It may be that you have one or more small earth leakages in the house, probably from watery appliances or outdoor lighting, which added together approach the trip current, and the cooker is just enough to push the current over the edge.

Was the cooker stored in damp conditions. Is it rather old?

We have this issue with a built-in Baumatic Oven. First it was just the grill/Upper oven element, which was replaced, and worked fine for about 11 months, then just switching on the oven using the temperature control trips the RCD. The appliance has 2 fans - one for the fan oven that blows hot air around the compartment, and another for cooling in the the control area, since that is immediately above the drop-down oven door, and blows thru the vents for keeping the control knobs, and storage units above the housing cool. This fan continues long after the oven heat is off.

One noticeable thing is that condensation readily occurs in the oven compartment, on the inside surfaces when, say, a joint, or casserole is left in the oven to cool down overnight - the metalwork obviously cools down faster than the food inside does, hence the drips on the sides and top.

Another possible factor is that when the element was replaced, it was noticeable that the rockwool insulation had been stained where the element came through the rear of the compartment to the back of the appliance where the connections were, where oven vapours had leaked around the fixings for the element.
I replaced the brown, greasy and sticky portions of the insulation with clean rockwool. These deposits were also found around the element connectors in this vicinity. It would seem likely that there would have been condensation in this area too, possibly entering the element assembly between the outer case and inner conductors where there is a simple ceramic plug as insulator.

The question I have is: would it be OK to have the oven supply (cooker circuit is not on the kitchen ring circuit), separate and not protected by the RCD, just by its own MCB?

I am sure some one will give you a diagram soon, but nitty gritty two large usage items both tripping the RCD likely it is what we call a neutral - earth fault. It is common for a bit of wet toast stuck in the toaster to cause the RCD to trip when kettle is used.

So go around the house unplug everything you can and switch off everything you can then try again with cooker. Since it is neutral switching off does not always disconnect things neither does switching off an MCB, fuse connection units normally have double pole switch but for rest it is unplug.

What happens is normally with no load neutral is same polarity as earth so even connecting both together will not trip a RCD. But as we load circuits neutral starts to rise above earth so now connecting neutral to earth will trip the RCD. With most plug in items easy to test just plug into to a socket supplied by another RCD but with fixed items like a cooker clearly not an option.

Elements often do fail by drawing in moisture but for two to fail very quickly I would look for the earth - neutral fault first.

Flyboytim said:

The question I have is: would it be OK to have the oven supply (cooker circuit is not on the kitchen ring circuit), separate and not protected by the RCD, just by its own MCB?

Click to expand...

Not the best option since the cooker may have an earth fault for which the MCB cannot provide the best protection. Using an RCBO instead of an MCB will give both over current and earth leak protection.

As requested

JohnD said:

It sounds like you have one RCD protecting all or several circuits. This is poor practice. It may be that you have one or more small earth leakages in the house, probably from watery appliances or outdoor lighting, which added together approach the trip current, and the cooker is just enough to push the current over the edge.

Was the cooker stored in damp conditions. Is it rather old?

Click to expand...

Oooo, that sounds like a proper electrician job, then.

There is 1 specific fuse on the RCD for the 'cooker'.

No, although it hasnt been used for 4yrs due to vacant property, it was a newish kitchen.

Upon further inspection, the Baumatic oven was plugged into the downstairs ring circuit, which has a 32A MCB and also a 6A MCB(upstairs lighting) on the first RCD. From the look of the blue flex from the oven it was designed to be a plug-in appliance (13A fuse) with a max stated rating on the oven, of 2400W.

The second RCD did not trip upon connecting, via a short extension, to the Cooker socket, and powering up the oven, on the cooker circuit, which is on a 32A MCB, with a 16A MCB for the upstairs ring and a 6A MCB for downstairs lighting. The upstairs ring has only low power, "dry" electronic appliances and lighting. Both RCDs are rated 80A 30mA.

So thanks Ericmark, I think I have my solution. We have not yet experienced a kettle/toaster trip, so I hope that changing the supply for the oven to the cooker circuit will solve the RCD tripping problem.

Thanks also to Bernardgreen who answered my query regarding the MCB on the Cooker circuit. From my successful test in the second para. above, and if I go the route in the 3rd para. I will still be protected by both MCB and RCD devices for the oven, but on RCD protected circuits only otherwise powering low power devices.

I presume that behind the kitchen units, beneath or near the Cooker Control and socket, I will find an unused cooker outlet. Are there any restrictions on adding either a fused spur or socket outlet to that circuit?

If it has been in storage fir several years I suppose it is possible the insulation of the heating elements has absorbed moisture.

Unplugging everything you can, and turning off the rest (especially immersion boiler, washing machine, kettle, outdoor lighting and sockets - anything watery) might let you turn on the elements one at a time for long enough to heat up and dry out.

Changing the circuit to an RCBO is much better than a shared RCD but yes it does need a qualified electrician who is a member of a self-certification scheme such as NICEIC (search websites). It is preferable to have your upstairs and downstairs lights, your upstairs and downstairs sockets, and your outdoor circuits, all on their own RCBOs, but this does work out more expensive, especially if not done at initial wiring. RCBOs will however very likely fit straight into your modern consumer unit to replace MCBs of the same width.

We have managed to turn the oven on at a low heat initially, then increase the heat gradually, and it has worked OK

I think it may be moisture that needs drying out, slowly.

Thanks for all your replies!