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I have a wall-mounted over-the-range microwave oven that is completely non-operational at the moment; from the user's point of view, it's as if it were unplugged, but it is. Unfortunately, access to its plug requires unmounting the oven. Furthermore, the circuit breakers in the fuse box are not labeled.

If I could get any response at all from the oven, I could use this response to find its circuit breaker by trial-and-error. As I already noted, I can't get any response from the oven by using its standard interface (the buttons on the front panel, opening the door, etc.), but I can remove the oven's front panel, and have a parts-list diagram. So my question is:

Is there some way (possibly with the aid of some suitable tool) to get a clear response? (I.e. a response that will change unambiguously when I toggle the right circuit breaker.)

(PS: I realize that there are other ways to deal with this situation other than identifying the oven's circuit breaker, but I'd like to know of any possible answers to the question above.)

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I'm surprised to hear that the outlet is not inside the cabinet above the microwave. Placing it behind the microwave when the microwave cannot be easily slid out (like a stove or refrigerator) make that outlet a hidden junction box and a likely code violation. –  BMitch Jan 6 at 16:24
    
It sounds like your circuit is blown; you should be able to locate the tripped breaker at your junction box if that is the case. –  Ethereal Jan 6 at 16:53
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According to the installation instructions, this model should be connected to the electrical system via a cord-and-plug. Look for the receptacle servicing this device behind, or in a cabinet above or adjacent to the device. Once you've located the receptacle, use that to troubleshoot the circuit. –  Tester101 Jan 6 at 17:34
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1 Answer 1

up vote 2 down vote accepted

A non contact voltage tester should detect voltage on any energized terminal or power cord. The tip will glow red when close to an energized power terminal or power cord.

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Just have an assistant hold the tester against some part of the oven or power cord that shows that power is present, then toggle the breakers until it turns off. Be careful inside the oven because there are usually some parts (capacitors) that store energy and remain energized even after power is removed, so don't touch any terminals with your fingers even if the voltage tester shows no voltage (it will only detect powerline voltage, not DC voltage stored in the capacitor). There are procedures for safely discharging the capacitor.

The pictured item is a Fluke tester, but your local hardware store will have a number of devices at various prices. I can recommend the Fluke tester, it works well and is not very expensive ($20 - $30) - I'd stay away from cheap generic testers without a known brand name since your own safety is on the line.

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In this particular case, since the interior light doesn't even come on when you open the door, my guess is that the fuse blew (its position is indicated in your parts diagram), so if you are comfortable with opening enough of the microwave to replace the fuse (taking into account the potentially dangerous charged capacitor), you could try replacing that fuse to see if the oven works. (it's possible that whatever made the fuse blow in the first place could still be at fault, so the replacement fuse might blow immediately too, but it might be an easy fix to get the microwave working again) –  Johnny Jan 6 at 16:53
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