microwave vs. power surge/neutral issue


Old 07-18-19, 05:53 AM
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microwave vs. power surge/neutral issue

I have a 2 year old microwave oven that had burned/melted plastic connectors at the temperature sensors/thermostats inside. The magnetron seemed to be very hot too. It was still working though when I found the burned connections.

I was wondering, if a microwave got excessive voltage from say a power surge or loose neutral, typically how would it fail?
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Old 07-18-19, 10:09 AM
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It's really hard to say, depends on how it was designed. However I would say that most, probably all, consumer appliances only 2 years old would have some type of sacrificial element like a fuse, link or MOV that would burn out before dangerous house fire type damage occurred. It's reasonable to expect that damage might be contained within the appliance itself.

Excessive voltage from a surge is usually a very brief spike, far less than 1 second and very high voltage, potentially thousands of volts. Generally will be more destructive to electronics & circuit boards than to "physical" electrical parts like motors.

Excessive high (or low) voltage from a loose neutral is going to be at most +110V over design values, but could be protracted over hours or days before it's noticed. Depending on the design of the device it might cause it to draw high current, low current, or no change at all. This means it could fail in a variety of different ways, or even multiple ways based on how each component is affected.
Old 07-18-19, 11:04 AM
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Typically the electronics would be damaged and clock and timer would be dead.
Old 07-18-19, 11:08 AM
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thanks for the replies.

Even with the high-resistant connections (melting plastic!) the microwave was fully functional. Hopefully odds favor that it would have been DOA if it got a surge or over voltage.

Ive been monitoring voltage at that outlet and it seems OK... its a multiwire branch circuit too, which is what prompted me to ask about lost neutral. I loaded up one leg of the multiwire circuit with 1500W heatgun and monitored voltage on the other leg and saw no abnormal swings.
Old 07-18-19, 11:13 AM
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High resistance melted connection typically occur over time not from a sudden surge.
Old 07-20-19, 06:18 AM
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Other possibilities:

Connection loosened and corroded (particularly if riveted together or manufacturing error) due to temperature and humidity changes and for that reason alone started to heat up excessively, no abnormal voltage or amperage.

Some of the oven heat got into the circuitry perhaps due to improper heat insulation or shields or mispositioning of magnetron.
Old 07-20-19, 10:38 AM
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Make sure the cooling fan is running.

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