One for the sparkies and others who are electrically inclined...

[Trav]

I was watching the teev last night while I had a nice roast lamb in the oven. I heard some funny noises coming from the oven and opened it up to see the element at the top white hot and sparking/flaming. It had bent down from the top of the oven where it normally sits.

I switched the oven off, but that made no difference. So I had to run outside in the pouring rain to switch the fuse off. As soon as I did this, it stopped smoking/sparking etc.

I had a look this morning, and the element itself is all distorted, still in the right shape, but it is covered with lumps and bums - looks like melted metal.

I guess I ahve a few questions.

1. what the fork happened?

2. why would it continue when I switched the power to the oven off? and

3. why didn't my fuse trip? Does this indicate that I have a problem with my fuses or wiring?

Thanks oven afficionados.

Trav

[Wood Borer]

Trav,

Fuses or circuit breakers will only break the circuit if their rated current is exceeded for a short period of time.

The temperature of the element is determined by the thermostat turning on and off. When current passes through the element it heats it up and continues to heat up the element. The thermostat works by allowing current to pass through the element when it is below the set temperature but cuts off the current when the set temperature is reached.

Let’s say your thermostat is faulty in that it does not cut off the current when the set temperature is reached. The current drawn by the element will not necessarily be greater than when it is first turned on from cold. (it will most likely be less) This means the fuse or circuit breaker will not “blow” because the current is within the limits of that breaker.

When you turned it off at the stove, are you sure the spectacular fireworks were still happening because current was still going through the element or was it still happening because the element was extremely hot?

I suggest your problem is with the thermostat on the stove and possibly the on/off switch also. Perhaps they are part of the same unit?

I hope your dinner wasn’t too spoilt or weren’t you in a position to judge after the incident?

[Jack E]

I agree with borer in that it is probably your thermostat. If it is the on/off switch as well and is shorted you will still have power to the oven until it is isolated elsewhere.
If it is not that you may have faulty wiring.
Are we talking fuses or circuit breakers here. No that it makes any difference but you said you turned it off.
How old is your house?

I am not going into who should fix it or whether you can do it yourself.

Cheers, Jack

[DavidG]

Element is stuffed and needs to be replaced.

Why it stayed on after switch off -
- Get an electrician to check it.
It could be a faulty switch
or an active neutral reversal (switch in neutral instead of active)
Element broke down to earth.

Either way this needs to be checked by a sparkie.

[HavinaGo]

I'd agree with DavidG.

Why no fuse fail: Rated current not exceeded for long enough. Note that the fuse/CB is rated to allow multiple elements to operate at once. The switch would only be rated for one element. Thus this is not inconsistent with the contacts on the switch fusing due to over current.

Unlikely to have Earth leakage protection on the oven ... hence detecting the current to earth is unlikely.

Supplimentary question:

To the sparkies ... Has this changed in new installations? ie do new installations now provide earth leakage protection for electric stoves, ovens and even elec hot water?

Fixing: Get someone to fix it as there are too many unknowns for a DIY repair unless you have the skills to do the diagnostics. Personally I'd like earth leakage protection on the oven (electricity, moisture, people all in the same place) but it may not be the norm and it may cost.

[Wassy]

My 2 bob is agreeing with David, get a sparkie to check/repair.

Cheers,
mat

[Termite]

Obviously the oven would rather have had a date with Nicole Kidman than with a lamb roast.

[Trav]

Thanks all. I'll get a service fellow out - they will need to replace the element at the very least.

I wasn't thinking of a DIY fix - more just concerned about the fact that this kind of thing could happen without tripping fuses.

JackE - they are circuit breakers, not fuses.

It is a near new Kleenmaid pyrolytic oven - disappointed that it is broken. Apart from that it is a great oven. I love the pyrolytic function. No more cleaning the oven - ever.

Trav

[Clinton1]

Your element failed. Heating up and cooling down over and over degrades the material it is made from. This is normal and it happens over time. A good element, as opposed to a cheap one, will last longer.

As for the rest.... NFI

[johnno402002]

Unlikely to have Earth leakage protection on the oven ... hence detecting the current to earth is unlikely.

Supplimentary question:

To the sparkies ... Has this changed in new installations? ie do new installations now provide earth leakage protection for electric stoves, ovens and even elec hot water?

I don't think that will change because of the nature of the heating elements and the way earth leakage circuit breakers work.

The problem with heating elements is that they tend to suck moisture in as they cool down, and sit unused.

When switched on again, they leak some current to ground. The element dries out as it gets hot, so the leakage gets smaller.

To protect a human from getting a fatal shock, the earth leakage circuit breaker has to trip the circuit if more than 30 thousandths of one amp goes missing. A damp element will leak more than that, and trip the circuit breaker. So basically the earth leakage breaker can't do the job.

regards,

John

[Trav]

Thanks all.

I have a service guy coming out tomorrow night to fix it up. I'll report back with his diagnosis (and repair cost :eek: ).

Trav

[Trav]

The service dude bailed on me last night - hopefully he will be here ebfore the weekend.

Trav

[soundman]

Its likely that the eliment whent kafoodla and took the controll with it.

In the distant past when electrickery was new nobody would consider installing an electric stove without an isolator switch nearby.
We gave that idea away for many years.
The idea is back.
Under the current rules ( that have been in force for a few years now) all stoves, ovens and cooktops now must have a redily accessable isolator switch fitted.
For reasons that have just become obvious.
If your oven was recently installed ther should have been an isolator swicth fitted.
cheers

[Simomatra]

Unlikely to have Earth leakage protection on the oven ... hence detecting the current to earth is unlikely.



To the sparkies ... Has this changed in new installations? ie do new installations now provide earth leakage protection for electric stoves, ovens and even elec hot water?

I don't think that will change because of the nature of the heating elements and the way earth leakage circuit breakers work.

The problem with heating elements is that they tend to suck moisture in as they cool down, and sit unused.

When switched on again, they leak some current to ground. The element dries out as it gets hot, so the leakage gets smaller.

To protect a human from getting a fatal shock, the earth leakage circuit breaker has to trip the circuit if more than 30 thousandths of one amp goes missing. A damp element will leak more than that, and trip the circuit breaker. So basically the earth leakage breaker can't do the job.

regards,

John

I agree with John

Be sure when the service person turns up that you that you insist on a good quality element, as this is the root cause of it all. The cheaper ones are not sealed properly and have thinner wall thickness in the element.

The thinner wall thickness and poor material are the cause of the fire works

Were I work in the offshore industry, we have monitoring of all our electrical equipment's insulation.

The galley is the worst offender for giving alarms when the equipment with elements are turned on. We heat the elements which give trouble and reseal them with either hight temperature silicone or HT epoxy.

Please bear in mind that this should only be carried out by a competent person.

Soundman is correct with the local isolator bit. If you don't have one it could be worth the expense to have one fitted.

Regards Sam

[Trav]

The service dude came around the other day and fixed it. The element had packed it in - you could see the filament through cracks in the ceramics and the outer metal cover.

The source of the problem was traced back to some dodgy electrical works - the sparky had attached a 10a plug and GPO to a 15A circuit that the oven ran on. The service guy fixed the situation and it was all sweet.

I did learn though, that almost every house will have 15A power cabling for the oven as all but a very few ovens draw more than 10A. You learn something new every day.

Now, if you are looking for 15A power to run your tablesaw, jointer and dusty, simply convince SWMBO that she doesn't need the oven anymore, whack a 15A GPO on the oven wiring and run a dirty big 15A extension cord down to the shed. :eek:

Trav