Bake element turned into a sparkler, required breaker be flipped

[bholmes]

While warming, the bake element in my Magic Chef 7858XVW lit up like it was burning. It proceeded along the element slowly, sparking like a sparkler. I turned the oven off (canceled the bake function), but it didn't go out. So of course I hit it with a fire extinguisher. Didn't go out. Finally, I thought to flip the breaker, and it quickly died.

I expect this is a common occurrence, but it scared the hell out of me.

Can I safely only replace the element? It seems that something else must have failed for the power not to have been cut when I turned the oven off.

The unit was installed in 1998. Is it just time for a new range?

Thanks!

[ECtoFix]

It didn't trip the breaker because, although the coil in the within the heating element was shorting to ground, the heating element's resistance never allowed enough amp draw to trip the breaker. 

What you saw is typical of a heating element failure.  You'll be fine by just replacing the element.

[bholmes]

Thanks! That answers my other question!

But shouldn't the power to the element have been cut when I pressed "Cancel" (just like the way it turns off normally)? It seems like some kind of relay must have failed for it to keep burning after I "turned off" the oven... I'm just concerned from a safety perspective.

[LearningTech]

15 minutes ago, bholmes said:

Thanks! That answers my other question!

But shouldn't the power to the element have been cut when I pressed "Cancel" (just like the way it turns off normally)? It seems like some kind of relay must have failed for it to keep burning after I "turned off" the oven... I'm just concerned from a safety perspective.

They do this on occasion, and yes the power should have been cut. I suppose there is something about the magnetic field of the rushing current that seems to hold the relay connected for a little bit after the control has cut the signal.

but it is just what they do 90% are fine after and will turn off like they should.

 There are a small percentage that will not heat after it is replaced, or will not turn off. You would have to get someone to test the power to  know for sure.

[ECtoFix]

@LearningTech, I'm a commercial appliance guy, so not overly familiar with residential design nuances. 

My question for you is, are BOTH LINES to the element switched off by the control in that oven?

The reason I ask is because some older commercial equipment designs that I've seen, only ONE leg of the 240v input is switched off instead of BOTH.  I never liked those designs since I prefer seeing BOTH lines getting switched off by the controls.  Having a lingering 120v still applied there directly from an input terminal block would cause exactly what he saw when the element fails and shorts to ground.

I'd provided my answer with a notion that maybe his old oven's design only breaks one leg to the heating element.

[LearningTech]

Older ones did only 1 line and one was always hot, but lots of people got shocked changeing elements when the unit was turned off, but not unplugged, newer ones have a what they call a double line break to help with saftey, and runaway temps when main relay sticks on. 

If you have a diagram look if it says DLB on the board anywhere.  Or sometimes called a L2 break

[ECtoFix]

5 minutes ago, LearningTech said:

If you have a diagram look if it says DLB on the board anywhere.  Or sometimes called a L2 break

No, I don't have a diagram either. 

He said it's a '98 model, so it might not be designed to break both lines.

 

[LearningTech]

Likely not at that age

[ECtoFix]

AH!  Found a wiring diagram!  Poor quality since was copied with a scanner...who-knows-how many years ago.

One leg of the heating element is NOT switched.  It IS hardwired to the input terminal block.  That means the element continues to receive 120v - even when the oven is turned off.

@bholmes,

You should be back in business by simply replacing the element.  Just be sure you do so with the circuit breaker turned OFF.

 

[bholmes]

It's so nice to get good advice from people that know what the the hell they are talking about. You guys are awesome.

All of this makes perfect sense, and based on your explanation I am comfortable just replacing the element.

Finally, the economic question- any idea of the expected lifespan of an oven/range? What type of failure would lead you to call time of death?

Thanks so much for your help!

[ECtoFix]

32 minutes ago, bholmes said:

Finally, the economic question- any idea of the expected lifespan of an oven/range? What type of failure would lead you to call time of death?

Thanks so much for your help!

When its part fails and a replacement parts are obsolete....unfortunately.

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People tend to replace appliances for aesthetic reasons such as when remodeling a kitchen.  Something that's shiny, new or has more up-to-date technology.  Or because that new stove matches their equally new refrigerator, dishwasher, etc. that they just bought.  What's ESPECIALLY true in the world of home appliances, it's been proven that "they don't make them like they used to".  That's just the sad truth.

Again, I don't work on residential stuff.  But that truth does apply to the commercial appliance market (my specialty) as well.  Engineers who design new equipment nowadays in BOTH markets have gotten better at designing stuff which only lasts just beyond the equipment's warranty period.  That's called "planned obsolescence".

Particularly for residential appliances, the threshold of initial purchase price vs repair costs tends to veer towards replacement of a unit as the more economically viable alternative.

If I were you, I'd hold on to that twenty-two year old range as long as you can.

 

[bholmes]

Thanks ECtoFix!  I appreciate the insight!

I ordered a new element, and that seem to have fixed the problem. The oven is operating normally.

The hardest part was cleaning up all the baking soda from the fire extinguisher hahaha.