heating element health

[jted]

Just a few words and thoughts about heating element health. Recently like in the past few weeks I replaced my 800 watt heating element because it was tripping GFCI receptacles. While troubleshooting the old element the only thing I knew to check was the resistance of the element. It was reading in the good zone just above 17 ohm's. I checked the resistance of a new element and it was 17.7 ohm's in a perfect world it should have been 18 ohms
Using Ohm's law which can be confusing since it has so many ways to find the same values this is the formula that I used and is not confusing at all. VxV / watts = resistance 120x120/800 = 18 Ohm's that is for a MES 30 " 20070910 old model.
Just like human health other factors come in to play but checking the resistance is like checking your blood pressure or pulse. A great place to start. I ran the numbers for several other wattage just so you don't have to. With the power off remove the leads to the element and put a lead from the multimeter on each one Turn the meter to the ohm's or omega sign on the meter and read your resistance
1000 watts =14 Ohm's
1200 watts =12 Ohm's
1500 watts = 9.6 Ohms
If yours is a above or under the the exact number it is not a real bad thing but much more than 10 % you should be prepared to replace your element. In my case Masterbuilt had the best price at 25.00 delivered for a 800 watt element.
I still have not figured out why my old element would trip the GFCI but I think it would break down under power. Jted

 

[bdskelly]

Great technical info here. Thanks! B

 

[johnmeyer]

Two things to add to your calculations.

First, many resistive substances change their resistance as they get hot. This is certainly true of incandescent light bulbs. If you measure the cold filament resistance, the V2/R Ohm's Law calculation will not give you the wattage printed on the bulb. The same may, or may not, be true of the heating element.

The second thing is that a multimeter may not be able to detect leakage resistance that is tripping your GFI. This again is due to the real world not always behaving according to Ohm's Law. The problem in this case is that resistance can be a function of voltage. There are lots of examples of this, such as a fluorescent light which, until it is heated at both ends, will not pass any current. However, once the gas inside is ionized by the starter (which was a separate circuit in the old days, where there was a starter can that you sometimes had to replace), the resistance drops dramatically and current can flow.

In the case of the heating element, if some sort of fault has developed, such as an insulation defect, the insulation may still measure as infinite resistance when tested with the few volts applied from the multimeter, but when you apply a high enough voltage, the insulation breaks down and current can flow.

Finally, most multimeter resistance measurements are taken with a small DC voltage applied. However, the element is obviously heated with 60 Hz AC voltage. As you know, when AC voltage is placed across a transformer, a current is induced in the other side of the transformer via the magnetic field that only exists when voltage is changing and therefore doesn't exist at all when a DC voltage is applied. This induced voltage can cause a current leak that will trip the GFI.

 

[jted]

John, I do believe the induced voltage does and has caused the leak you spoke of. I would like to know your thoughts on why when external heat is applied to the element it will not leak enough to trip the GFCI. Jted

 

[johnmeyer]

John, I do believe the induced voltage does and has caused the leak you spoke of. I would like to know your thoughts on why when external heat is applied to the element it will not leak enough to trip the GFCI. Jted

I am not quite sure what you mean by "when external heat is applied to the element," but if you mean that you can get it to work without tripping the GFI if you pre-heat the element with a hair dryer and then plug in the smoker, that would seem to indicate possible condensation or moisture somewhere inside one of the wiring boxes, or somewhere else where the one of the wires is exposed.

 

[jted]

John, The induced heat was from a hair dryer. I had this start several years ago and I had thought it might be moisture in the element but after countless hours heating I thought it would have evaporated. With the GFCI being so sensitive I will probably never definitely pin it down. I am just happy it is fixed. Jted

 

[clifish]

Bringing this back to the top, my smoke hollow (mes) has a 1500W element so I believe the resistance should be 9.6? My confusion is on my meter setting. I know it is on ohms but there are multiple settings. see below and let me know what you think I should set it at?

 

[dsk]

The 200 ohm setting is the lowest you have. Use that one.

 

[clifish]

The 200 ohm setting is the lowest you have. Use that one.

this is what I get at 200 not even close to 9.6

 

[dsk]

Are you testing this because it is not working? Because that would make it not work.

 

[clifish]

the original controller melted, got a new one and could not get the smoker above 275...empty

 

[civilsmoker]

This might help....

Need to make sure nothing is connected to the heating element including fingers holding it to the leads when measuring the ohms.

If you look at these numbers, the 1800 Watts is where the Aubers controller limits out for 120 (ie 15 amps).

All the prefabricated elements are already set for a specific amp draw. The above is very important if you are building your own heating element (I did for my heat treat oven).

 

[clifish]

This might help....
View attachment 688117
Need to make sure nothing is connected to the heating element including fingers holding it to the leads when measuring the ohms.

View attachment 688118
If you look at these numbers, the 1800 Watts is where the Aubers controller limits out for 120 (ie 15 amps).

All the prefabricated elements are already set for a specific amp draw. The above is very important if you are building your own heating element (I did for my heat treat oven).

My reading was with the element removed and on a carpet.

 

[dsk]

Your meter is saying connect test leads in the second photo. I don't know if that warning goes away once they are in, but make sure they are fully seated.

 

[dsk]

Also, at 120V, a 61.7 ohm element would only create about 235 watts, far to little I think to take the cabinet to 275F. Handling the element while removing it may have made a slightly bad element into a truly bad element.

 

[clifish]

Also, at 120V, a 61.7 ohm element would only create about 235 watts, far to little I think to take the cabinet to 275F. Handling the element while removing it may have made a slightly bad element into a truly bad element.

cheap enough for me to replace it...thanks

 

[mike243]

The older refridges will trip a gfi, any voltage leakage to ground will trip it, a lot of the owners manual had a notice about not using them with a gfi, coarse a new 1 will also but some wont these days, lot of changes over the years

 

[civilsmoker]

My reading was with the element removed and on a carpet.

What Dsk said…..it tells me the element is toast….likely burned up in a spot under the insulation so you can’t see the bad section

 

[clifish]

What Dsk said…..it tells me the element is toast….likely burned up in a spot under the insulation so you can’t see the bad section

I think you are both right, one side of the insulation is definitely cracked. For $32 I will replace the element and the thermostat.

 

[civilsmoker]

I think you are both right, one side of the insulation is definitely cracked. For $32 I will replace the element and the thermostat.

Cracked insulation indicates oxidation to the element wire……….