Microwave combi oven tripping RCB?

[Morrisman]

I was using the convection oven part of my combi tonight, 230c and 15 minutes into my roast chicken the power went dead, whole house. I nipped into the garage, and found this had flipped to ‘off’. It wouldn’t reset until I flipped all the other breakers off, then it would. I flipped them all back up, one by one, went in and restarted the combi oven, and 30 second later, all power went off again.

I’m a bit clueless with RCB stuff, so does this indicate a ground fault on the microwave itself? The big switch on the right is the RCB, the small black ones are conventional circuit breakers?

What if there’s a short circuit, will just the relevant black one trip?

The microwave is only a year or two old, but I shall have a look for anything obvious wrong with it tomorrow like a melted cable etc.

 

[Seadog]

Heater element short circit.

 

[brightspark]

live to earth fault tripping the rcd the miniature mcb tend to only go if theres a live to neutral fault or are overloaded

 

[Morrisman]

live to earth fault tripping the rcd the miniature mcb tend to only go if theres a live to neutral fault or are overloaded

I’ll dig into it tomorrow, see if there’s anything obviously melted.

 

[Dozzer]

I was using the convection oven part of my combi tonight, 230c and 15 minutes into my roast chicken the power went dead, whole house. I nipped into the garage, and found this had flipped to ‘off’. It wouldn’t reset until I flipped all the other breakers off, then it would. I flipped them all back up, one by one, went in and restarted the combi oven, and 30 second later, all power went off again.

I’m a bit clueless with RCB stuff, so does this indicate a ground fault on the microwave itself? The big switch on the right is the RCB, the small black ones are conventional circuit breakers?

What if there’s a short circuit, will just the relevant black one trip?

The microwave is only a year or two old, but I shall have a look for anything obvious wrong with it tomorrow like a melted cable etc.

View attachment 442596

Had same with my Panasonic combi, was fine on Microwave but would trip on oven mode!
Turned out to be duff heating element as @Seadog has indicated.

 

[sparkysy]

Could be a live earth fault on the microwave. It could also be a fault elsewhere and the high current of the microwave is driving more current through that fault.
That is quite an old board and RCD so could be becoming rater more sensitive to leakage and tripping early, also could be combined earth leakage from all the circuits and the microwave is enough to put it over the threshold.
Yes MCB protect you from short circuit and overload. RCD RCCB protect you from live/neutral to earth faults. RCBO's do all of the above with the added bonus of only the affected circuit tripping and not the whole installation.
Sy

 

[brightspark]

those old mem and crabtree rcd are a dead loss and have been even from new and can be a pig to set even with new wiring still a fault on microwave probably you will have to do an insulation test on it when it trips as the element gets hotter the insulation breaks down and off they go similar to oven elements

 

[Seadog]

I always do an earth leakage test on anything with an element that's tripping an RCD.
Nine tines out of ten that'll be where tge fault is. They don't make them to last any more.

 

[brightspark]

all i do is if called out is test the suspect appliance when cold if no faults run it for 5 minutes then test again and take the insulation readings again if its down to earth theres your fault

 

[Morrisman]

all i do is if called out is test the suspect appliance when cold if no faults run it for 5 minutes then test again and take the insulation readings again if its down to earth theres your fault

Is this something I can do with the a basic garage multimeter?

 

[Robotstar5]

Is this something I can do with the a basic garage multimeter?

No, you need an insulation resistance tester, commonly called a "megger".

 

[Red'n'Black]

If you don't have a Megger, another quick test is to pull the connections off the heating element and see if the RCD still trips.

That's how I did a mate's washing machine before we spent any time or money on it, once the old element was out it was obviously shot, casing was all split.

 

[ajlelectronics]

Standard failure mode of an element is short to earth. My Whirlpool oven did that about every six months with pattern parts. The Neff I have now seems to manage a year or two between changes.

 

[aesmith]

Is this something I can do with the a basic garage multimeter?

You could test for resistance between N and E. If there's any sort of contiuity it shows there's a fault. But as it tests at a really low voltage, open circuit reading doesnt necessarily mean there's no fault.

We had a similar fault on a tumble dryer. Failed ceramic insulator meant the heating element touched the metalwork right near to the N end. So heater worked apparently normally, no overload, but RCD tripped immediately.

 

[Morrisman]

I just fired it up again, it lasted one minute, then tripped. I quickly hooked up my meter, switching settings until I got some sort of reading. The number shown is slowly dropping, it was 650 an minute after it had had tripped.

Does this look like a clue?

The oven is 2 years old, cost my dad £500 from Curry back then. And I inherited it when he died. I’m sure he bought an extended warranty, like he did with everything, but I can’t find it.

 

[ajlelectronics]

Warranty will not cover consumables. A new element is a tenner for a pattern, perhaps twice that for a branded. Just swap it out, it will be four self tappers to expose it, one screw and a couple of tabs to remove it. Ten minutes work.

 

[Dozzer]

You need to get a connection directly onto the + & - of the heating element, there will be smoothing caps and maybe a bridge rectifier or resistor on the mains in.
It shouldn't be to hard to take the cover off and find the power leads to the element, disconnect the wires going to it and then use the Ohms function Ω on the multi-meter. lower the better, if there is around 20-50Ω it maybe ok, if it goes dead short or close to its dead,

Dont normaly do angry pixie stuff but this is manageable even for a numpty like me

 

[Morrisman]

Warranty will not cover consumables. A new element is a tenner for a pattern, perhaps twice that for a branded. Just swap it out, it will be four self tappers to expose it, one screw and a couple of tabs to remove it. Ten minutes work.

I shall tear it down later and have a look. I did much the same with a conventional oven a few years back, came close to simply scrapping it and buying a new one, but then decided to do research. £40 and it was a good ‘un again.

 

[Hotstuff]

Hi @Morrisman

Sadly, you can’t diagnose a mains powered appliance insulation resistance problem with a multimeter.

As others have mentioned, you need a “megger” test instrument that would apply twice the nominal supply voltage (500V) during the test.

Metallic elements such as those used in cookers or immersion heaters are notoriously unreliable when supplied via a 30mA RCD.

The RCD can be tested if you can find someone with an RCD tester that includes the ramp facility but in all honesty, it’s more likely that the element is faulty and will need to be replaced.

 

[ajlelectronics]

You need to get a connection directly onto the + & - of the heating element

And once you have got in there, you might as well just fit the new one!