[jumbuck10]

Update:
Replaced 1 x Fan Forced Element so now I have: 1 x 1550W (new) + 1 x 2000W element (originally 2200W (6 mths) + 2000W)
The MCB trips on the Fan forced (2 fan elements) and Super cook (all 4 elements). This happens from a cold warm-up to 150C.
It doesn’t matter which of the two 2200W or 2000W I swap out – it doesn’t make any difference.

However, the Fan+Grill function does not appear to trip the MCB.
I have also noticed that on 2-3 occasions the Fan force setting (1550+2000W) element did not trip the MCB.

I am stumped. I can’t see any obvious damage to the wiring and connectors, although the plastic shielding on the end terminals have broken off due to age.

I have ordered a new oven thermometer to double check the oven thermostat settings but I don’t think this is the problem since there are no issues when fan-forced mode is not used. The cooling still appears to be running fine.

Oven Relay Circuit Board? Clock circuit board issue?

[jumbuck10]

Yes, it’s really strange. The breaker is rated with 20A 4.5kA. – wonder if it is just sensitive and trips at 16A or something.

If the rear fans have an earth leakage then it should trip it straight away wouldn’t it?

As for the Fan Grill tripping – could it be cooling fan causing the trip as it switches on?
The cooling fan thermostat is rated at 80C. So if the back of the oven hits 80C it should go on. I will have to put the meat thermometer on it somehow. The problem is the thermometers are never that accurate.

Do you know what the 125 deg C printed on the cooling fan means?

I’ll have to do more grilling – might have to try chicken wings next.

“your saying the trip goes and does not reset for a few minutes
but previously you said it was not an RCD or a RCBO so it does not have an earth leakage trip”
Nope, not RCD or RCBO – I checked the specs.
Trip not resetting happens on a hot oven.

[jumbuck10]

I set it on fan force at 100C – an click! power cuts out.
So we confirm that it’s an electrical trip. CB flicks back up straight away.
That’s problem one. The element calculations make sense but I am wondering if the fans have something to do with the trip too.

[jumbuck10]

Thanks Dave.
It sounds like I should replace the element with a lower rating in any case.
I could be dealing with multiple problems here.

I have been doing lots of roast potatoes lately as I watch the oven behaviour – the Mrs is getting a little sick of roast potatoes 😀

Last night I checked out the fan grill function and watched the rear elements – they didn’t glow hot and the leaflet I have says it doesn’t use the rear elements. (geez it was hard to find). https://www.smeg.com.au/smeg_com/docs/common_pdf/C9GM.pdf

If it doesn’t use the rear elements then the only other conclusion I can think of is that it is a heating issue rather than electrical.
rationale 1: CB trips because the safety temperature reaches the cutout temp. It takes a minute or so before the CB can be flicked back on without it tripping. So it is likely to be the safety cutout thermostat has cooled down a little.

rationale 2: CB trips because the safety temperature cut-out reaches the cutout temperature. The fact that it trips with the Fan grill function (at about 125-150C) is due to the fact that there is better air circulation (but then this doesn’t explain that the convection mode can reach up to 220C).

[jumbuck10]

The plate says Max load 4.1kW – that is all I can find.
So by my calculation 4100 / 230 = 17.8 A – a 20A circuit breaker should do the trick and it has been for at least 8 years until now.

So if fan forced elements are 2200W (left) and 2000W (right) then we are effectively 4.2kW (yes have had a couple of service guys come through over the years). Smeg ones are supposedly 1550W each but I have also been told that certain C9GMXA models have had 2000W elements – not sure how accurate that is. This would explain why the fan force function trips the CB.

But what has me stumped is that the CB also trips if I put it on Grill & Fan function (symbol) which I presume runs the Top Grill with 2 Fans and no fan force element.

I also just checked the resistance of the fans when idle but I don’t know what the correct range should be.
Fan force fans: approx 113.5 ohms each
Cooling fan: 154.5 ohms, also noticed that the fan serial had what appears to be 125 degrees C stamped

Just found something interesting from Smeg documentation.
Cooling Fan: 20 Watts
Rear fan-force fans: 25W x 2.
[TABLE=”align: left, border: 1, cellpadding: 3, width: 500″]
[TR]
[TD]Function[/TD]
[TD]Circuit Trip[/TD]
[TD]Element[/TD]
[TD]Max Wattage[/TD]
[TD]Current Amp[/TD]
[/TR]
[TR]
[TD]Convection[/TD]
[TD]N[/TD]
[TD]Top & Bottom[/TD]
[TD]3050[/TD]
[TD]12.71[/TD]
[/TR]
[TR]
[TD]Fan Grill[/TD]
[TD]Yes, about 150-175C [/TD]
[TD]Top (inner & outer) with 2 rea fan [/TD]
[TD]2900[/TD]
[TD]12.09[/TD]
[/TR]
[TR]
[TD]Fan Forced[/TD]
[TD]Yes, at 125-150C[/TD]
[TD]2 x Rear Element + 2 x Fan[/TD]
[TD]3080 (assuming 2 x 1500W elements)[/TD]
[TD]12.84[/TD]
[/TR]
[TR]
[TD]Supercook[/TD]
[TD]Yes, 125-150C[/TD]
[TD]Top, bottom, 2 x Rear[/TD]
[TD]4480[/TD]
[TD]18.67[/TD]
[/TR]
[/TABLE]

[jumbuck10]

New style MCB 20 Amps.
Trip Interrupting Capacity 4.5kA

Not an RCBO.

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