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Recently, our oven was left on all day, and sometime during the day it tripped the breaker.

Now, whenever the oven is used (only for heating pizza, so 10-15 minute timeframe), the breaker trips during the preheat phase. If I reset the breaker, the oven functions normally.

Is this more likely to be a wiring problem, or an oven problem? Is there any danger in using the oven after resetting the breaker?

Clarification - The stove top (ceramic elementless) works fine. It also functioned normally previous to it being left on for an extended period. The home was built in the late 90's, and while the stove is a newer model, it was there when we purchased the home in 2010, so I do not know the provenance.

It is only when the oven is used that the breaker trips. I will have it checked, however.

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Stop and get things checked out!!!

The breaker is there as a safety protection device - not as a minor inconvenience. If the breaker is tripping there is an overload or short circuit some place that needs to be addressed. Electrical safety issues are nothing to mess around with. You could get severely shocked or killed as a result of an electrical fault. Call in a qualified electrician today to evaluate the situation and help with the proper fix.

The problem could be any one of the following:

  1. oven
  2. oven power plug
  3. wiring feeding power to the oven
  4. circuit breaker in the main junction box
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The problem could be either the oven or the wiring. The oven could be using more amperage than the circuit breaker is rated for, and thus tripping the breaker. Or, the problem could be with the wiring (for example, damaged insulation causing unwanted current in the wire), or the circuit breaker could be failing.

Standard circuit breakers are designed with a certain amerage-time trip-curve. For example, a 30 A breaker should never trip while it flows 30 A, and at twice the rated current (60 A), could trip after as long as a minute. It may trip within a second only for ten times the rated current.... This is the expected behavior, and does not indicate a malfunction. For an example curve, see this Siemens document. Your oven could be using more than the rated current when on, but since it is only continuously on during warmup, it would only trip the breaker during the preheat stage.

Newer installations could have special types of breakers, such as GFCI or AFCI. But, this would be unlikely for a dedicated appliance circuit. Loose connection could cause series-arcing, but this shouldn't trip a standard circuit breaker (it would reduce the average power being used). If the appliance was connected to an AFCI breaker, the breaker could be detecting the arc and tripping.

In any case, correct the problem soon. The circuit breaker is likely not designed to be used as a switch, it has a limited number of trips during its lifetime. Also, the fact that it is tripping signals that something is wrong (and probably overheating), and likely unsafe (possibly causing a fire).

Electricity is dangerous, and you should only attempt repair if you are comfortable around electricity and know the proper safety precautions. working in the circuit breaker panel is especially dangerous, and you should wear a face shield and other protective equipment, in case there is an arc, or a circuit breaker explodes.

My gut feeling is that the breaker is likely failing, and should be replaced. I think this because ovens will usually "fail open" causing their current to go to zero, not increase their power used. Also, running the oven all day would put additional stress on the breaker. The oven is likely powered with 240 V split phase electricity (common in the United States). In this case, it would have two "hot" wires, one "neutral", and one ground.

I would go about troubleshooting with the following steps:

  1. Verify the breaker is of the correct rating. Examine the information plate on the back of the oven for the maximum current that it requires. Ensure that the circuit breaker is rated for that same amount of current, or the next higher standard amperage. The standard breaker sizes include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110 A, et al. Read the NEC codebook for details on which breakers you are allowed to use. If your circuit breaker is undersized, then verify that the wiring and plug is sufficiently large to support the needed current, and make the necessary corrections to the setup.

  2. Measure the actual current going to the oven. In the circuit breaker panel, attach a clamp-type ampmeter to one of the hot wires going to the oven, and measure its current while the oven is turned off and also during the preheat. The current while it is off should be near zero, and the current when it is on should be less than the oven's maximum current. Repeat this with the other hot wire.

  3. If the preheat current is less than the rating of the circuit breaker, the circuit breaker is faulty.
  4. If the current while the oven is off is significant (>0.3 A), then either the wire to the oven is bad, or the oven is damaged. Unplug the oven, and check if the current goes to zero. If it doesn't then you have wiring issues in your home.
  5. If the off-current is near zero, and the preheat current is more than your oven is supposed to use, then your oven needs repairs.
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Thank you for the detailed answer. I would add that the oven worked completely normally before this point, it is only since the oven was left on for an extended period that it has evidenced this problem. – JohnP Aug 2 '13 at 18:41
Yes, I saw that you mentioned that. Leaving it on for a long time can certainly stress a circuit breaker and cause it to fail. In my experience failing heating elements use less and less power (and soon after fail quite catastrophically), which wouldn't cause the breaker to trip. – Pigrew Aug 2 '13 at 18:45

Final resolution:

Father in law came over and we did all the measurements above, starting from the oven outward. As it turns out, we could have saved time by starting at the panel first. However.

At the panel, the oven and the air conditioning unit are both being run off of aluminum wiring instead of copper. As was explained to me, the disadvantage is that aluminum expands and contracts, and can eventually loosen the fastening screws. He also told me that the breaker is heat related, i.e., if the breaker gets too hot, it trips.

The screws on the wiring had loosened, and had a reduced contact point. This caused more current to go through a smaller area, which increased the heat, which caused the breaker to trip. Tightened up all the screws, and fixed the problem.

I won't accept my own answer, as all the others contributed, I just wanted the answer here for archive/future research purposes.

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Aluminum wiring is tricky stuff. You have got make sure that everything connected to it is specifically rated to use it (most large breakers are, but not all) and it's generally also a good idea to use anti-oxidant paste (made for the purpose, found in the electrical section as you'd expect) on the connections as well. – Ecnerwal Dec 13 '13 at 20:37
@Ecnerwal - Yeah, he explained about the paste, and seemed to feel that what was on there was enough, and didn't need to augment. Thanks, forgot to add that in. – JohnP Dec 14 '13 at 15:00

A simple test will determine whether the source of the problem is the oven or the wiring. If it is wiring, the most likely cause is the circuit breaker itself.

A clamp on ammeter like this placed around one of the wires in the breaker box will instantly read how much current is flowing through the wire. (It works by magnetic coupling, so it is safe to touch and does not harm the wire.) Note that clamping around a wire pair (such as a cord) will normally read zero. That is, the power source wire must be separate from the return (neutral) wire for the ammeter to work. The easiest access to this for an oven or any other household circuit is inside the breaker panel—easily opened by undoing 6 or so screws.

Clamp on the ammeter to one oven "hot" wire and turn on the oven. Observe it for a minute or so—as the oven element heats up, it should change resistance and therefore the current, starting out high and decreasing as it heats. If the current is well over the breaker value (that is, for a 40 amp breaker, 50 amps would be "well over"), the oven is defective—or maybe a mismatch for the circuit. Check the oven rating tag (probably on the back) or the manufacturer's website. The other over wire should read almost exactly the same current.

If the current is well within range (for example, 25 actual out of 40 rated) and the circuit breaker trips, replace the circuit breaker: it is fatigued and ready for the great circuit breaker yard in the sky.

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