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[combo52]

Bad Heating Element In A Filterater Dryer

The contact is corroded and burned from long use with old connections, when a heating element starts to fail and then fails it is drawing LESS current. The damage to the connections happened over a long period of time, the element failed in less than one minute.

 

[jetcone]

Sorry

but I think you are wrong about that. A failing part draws more power at the moment of failure causing it to melt, that's what a short is. A vacuum tube draws more power on the failing end, it glows the brightest just before it winks out. A short which is the failure of a heating element is  a process of direct contact to ground with no resistance , infinite current, definite failure.

 

You cannot punch a hole in chromalux like that with less current , only more current than the material was designed to handle.

 

"when a heating element starts to fail and then fails it is drawing LESS current" I think you are thinking of an aging element who's resistance increases, as the resistance increases the running temperature climbs causing the oxidized terminals. 

P=I^2R , as the resistance climbs in the tube, holding the voltage constant ( i.e. as the tube ages) the power output ( or running temperature in this case) increases.

 

Failure is a catastrophic event that happens quite quickly. 

 

"the tube was dying it drew too much current and stressed the contacts causing them to corrode"

 

I probably said that wrong before , What I should have said  was: "when the tube was dying it was running hotter than design" and that stressed the contacts". 

But the failure was an eventual short to ground. 

 

 

 

 

 

 

 

[this post was last edited: 11/19/2015-20:58]

 

[combo52]

All Very Nice But Not Correct

The element was drawing less and less power as it aged, yes when it finely shorted it drew more power for a few seconds at best, but the rust and corrosion on the terminals happened over a long period of time may be even years.

 

We have replaced thousands of shorted bake elements in ovens and thousands of elements in electric dryers and have almost never also seen a burned terminal or other connection in the circuit that feeds the failed element, one has nothing to due with the other.

 

John L.

 

[jetcone]

HUH?

  I=V/R. See the video. The element is about to fail, it has a hot spot. The hot spot represents a place where the nichrome wire is shorting directly to ground through the metal sheath, current is no longer passing across the whole length of the element to the end contact. As such the resistance has dropped in that length to the hot spot, while the voltage has remained constant, and so the current has increased through the nichrome to that point. I=V/R.

 

That means P=I^2R , as the current increases the power jumps by the square of current hence the glowing ready to fail element.

 

 

Tell me how does it draw "less power" ??

[this post was last edited: 11/20/2015-08:35]

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[jeff_adelphi]

Jon

Remember when a 240 volt circuit shorts to ground it's only a 120 volt short.

 

[jetcone]

Yes

Jeff you are right - but the current draw is instantaneously higher and you are no longer going thru the circuit breaker .

 

I wrote that in haste loading the dog into the truck, this is the correct analogy :

 

The circuit breaker doesn't know that the shorted element is going to neutral or ground. But where the break occurs in the element the resistance will be lower  - below the circuit breaker to trip. So it keeps drawing and shorting to the metal sheath. So since the voltage remains constant and the resistance is reduced then the current draw has to go up. V=IR. Thats what makes the red hot spot, not less current! Wether it draws long enough to trip the circuit breaker before the element flames out is anybody's guess.

[this post was last edited: 11/20/2015-14:37]

 

[combo52]

HUH?, Do I Have To Speak Louder, LOL

That hot spot you often see in a sealed element IS NOT SHORTED TO GROUND, it is a thin spot in the element and it means that the element is about to fail. When the element has a hot spot in it like this the total wattage is less than a normal element [ this is very easy to test and prove ]

 

When the element finely fails it sometimes shorts to ground so you have 120 volts at this point to ground so you have 1/2 the element drawing 1/4 the wattage of the full element if it were operating properly if it fails anywhere near the middle.

 

Question Jon, when the element is shorted where is the power coming from if it is not going through the circuit breaker ????????????????, maybe from the ground wire connected to your cold water pipe, you might be on to a source of free power, LOL.

 

John L.

 

[philr]

I don't want to say anything that makes no sense or that implies that this element is shorted to the ground or not (a multimeter would tell if the element is shorted!)...

 

But I'm wondering if the element fails near the connector, then doesn't the place that shorts near the connector get higher wattage because of low resistance between the shorted terminal and the shorted spot on the outer part of the element?

 

I don't know if that terminal is linked to the thermostat side or if it's the longer part of the heating element that is?

 

I'm not too good in physics but I think that a 240 V element connected on 120 Volts draws about 1/4 of the wattage it would draw on 240 volts and that if it shorts in the center part, both sides would draw half of the wattage (or double of the wattage between both terminals if connected on 120 volts)?

 

If it fails at the 1/4  of the length, then I guess one side will draw the same wattage on 120V as the whole length would on 240 and the other 3/4 would draw 3 times less?

 

Is that right?

 

[jetcone]

This should be

clearer for everyone see video:

 

Phil I think where it shorts to the metal sheath is dependent on the packing of the magnesium in the sheath, my dad used to work in this problem, the packing is crucial to the life of the element. If I remember correctly its been years but  - the arcing to the sheath is what causes the magnesium to change, I think the arcing reaches an ignition temperature  of the magnesium once you do that-- look out Lucy.

 

John I don't how you figure your numbers, the physics of the situation is the physics of the situation.

 

again: 

The circuit breaker doesn't know that the shorted element is going to neutral or ground. But where the break occurs in the element the resistance will be lower  - below the circuit breaker to trip.  So since the voltage remains constant and the resistance is reduced ( just as you stated above )  then the current draw has to go up. By Ohms Law : V=IR. Constant voltage with reducing resistance means current has to go up - otherwise V does not equal IR. 

 Thats what makes the red hot spot, not less current! Wether it draws long enough to trip the circuit breaker before the element flames out is anybody's guess.

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[this post was last edited: 11/20/2015-14:48]

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[combo52]

Interesting video Jon

But the situation that is being described is not quite the same as a 240 Element in the dryer were discussing. In the video they have 277 V on one side going to neutral on the other side so if the element shorts somewhere along the way you could have a higher amp draw for a while. But the main thing to keep in mind even when this happens the short is only going to last seconds or a minute at best.

 

There is not enough time to do any damage to the terminals even if the amp draw goes up slightly. The other thing to keep in mind is that an electric clothes dryer is normally on a 30 amp circuit it drawls nearly 25 Amps the whole time it's running and heating. If there's much of an amperage increase at all it'll quickly trip the circuit breaker.

 

It also does not matter whether the current flowing through the circuit breaker in your home is going to the ground or to the neutral they are really the same thing [ as they are connected together in your electrical panel anyway ] the circuit breaker knows how much powers going through and it will trip if it detects an overload.

 

John L.

 

[combo52]

Good Video On U-Tube

Showing a 240 volt bake element in a GE wall-oven that has a hot spot in it.

 

It is posted under Houston Home Inspector.

 

In the video it shows a bake element with a hot spot before the element actually burns out, often when this happens the inner nichrome wire gets so hot it melts the outer sheath and shorts to it as it fails.

 

The interesting thing is when the element is in this pre-failure stage the element is drawing less total power and putting out less total heat and once the element fails either by just burning out and going open or by shorting to ground it will only last a few seconds to less than a minute, not long enough in any case to cause any damage to the appliances wiring.

 

This video is much more relevant to what happened to the element in the Frigidaire Filtrator Dryer.

 

[jetcone]

Link???

Link??

 

[combo52]

Link?

Hi Jon, if you click on your link in reply #22 it will come up.

 

[jetcone]

Oh so you finally watched that

Good John.

 

Now show us how there is less current. 

All you've done is say there is less current.

 

I think I will have a transmission for you when I get down in January.