Bread Maker trips RCD when baking cycle begins

**Romulus** · 07-08-17, 07:41 PM

The bread machine is a Breville BB400 - We've had it for quite a while, and it's also been in storage for about 2 years.

It worked O.K. when it was last used.

It turned on alright for programming - then it went through the kneading and rising cycles O.K, but then tripped the circuits RCD as soon as the Bake cycle began.

I suspect it might be the element.

Anyone know what value resistance the element should have if it's O.K. ?

I've read somewhere about the element having absorbed moisture which was causing the fault, and it's been fixed by heating the element up to drive out the moisture and then sealing the ends with high-temp silicone.

Anyone know if this works ?

And if it's not the element, are there any other common faults this model had ?

Regards,

R.

**Skepticist** · 07-08-17, 11:19 PM

If it has a 'cemented tube' type heating element, they are notorious for absorbing moisture when left unused for a long(ish) time which lowers the insulation resistance to the point where the earth leakage can trip an RCD. Get hold of a 'megger' or someone who has a megger to check the element's insulation resistance. If it's only moisture related leakage (I assume it only trips the RCD and not the circuit breaker which means no overcurrent), the element can fixed by heating it for some hours to drive out the moisture. EG by removing it and baking it in the oven or by powering it up on a circuit not protected by an RCD.

Of course, if it's a full-on short circuit fault to earth then it's time for a new element.

Never heard of using silicone on them before though.

The resistance between the element core conductor and the outer tube will be less than 10k ohms measured with a 500V megger for it to trip the RCD. Cooking the element should raise that to around 1Mohm or more, the element end to end should be something like 50-100 ohms (depends on the power rating).

**ammlione** · 07-08-17, 11:29 PM

I could not find many spares easily for mine, last weekend I bought another breadmaker from Aldi, very similar to the BB400 for $89 and I stored it in the garage. The blades and pan of my BB400 are almost shot, so I don't expect it to survive a lot longer, maybe a year more if I'm lucky?
Overall it was a great machine, had 2 of them in the last 15-17 years (its been a long time..)
Good luck with the repair!!

**Romulus** · 08-08-17, 11:06 PM

@ Skepticist - Thanks for that.

Pretty much your standard mineral-insulated element by the look of it.

Resistance between element core conductor and outer tube ( 0.05 M Ohms ? )

Element end-to-end ( 120 Ohms ? ) - Appliance's rating is 470W

Had the Dick, or is it worth trying to heat it up ?

R.

**Skepticist** · 08-08-17, 11:37 PM

Almost certainly moisture is the culprit especially since it was out of service for a long time.
Element itself sounds fine so, if it can be completely removed put it in the oven at 150C or so for an hour then measure the insulation resistance again (after it cools down) - should show signs of improvement.
If it can't be removed you could heat it up from an outlet that's not RCD protected and you'll soon know if it's just borderline leakage or a full-on breakdown
Still not sure about using silicone on it because of the temperatures those elements can reach (can be enough for dull red heat in the tube) and even high temp silicone might not survive that, could even break down to form a poor enough conductor to cause more RCD tripping. Because of the huge heat variations the tube has to be able to breathe too.

Oven's the best test to see if it improves with heating first.

**Skepticist** · 13-08-17, 12:53 PM

Bump - Just wondering whether it was a win or a melt-down?

**Romulus** · 17-08-17, 09:51 AM

@ Skepticist - Sorry for the late reply - I've been away for the last week.

Yeah, it's A.O.K. now thanks.

It was enough of a P.I.T.A. removing the base & top cover off, just to take the photo & the measurements - I wasn't gonna risk taking the element itself out to bake it in the oven, in case I ended up breaking something.

So I just put it all back together and then put it on a circuit without RCD protection.

Set it manually on the Bake cycle for 10 mins, and tried it again with the RCD.

Works fine again.

I would've liked to take a second pair of readings for comparison, but I couldn't be bothered dismantling it again ( leave well enough alone ).

Once again, thanks for your help.

R.