microwave keeps blowing outlet fuse

Old 10-07-02, 08:09 PM
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microwave keeps blowing outlet fuse

Out of the blue, our microwave oven keeps blowing the fuse of the outlet that it is plugged into...We have had this unit for over 3 years and have NEVER experienced this before.

I plugged the microwave into another outlet and it seems to work fine...

Any ideas why this particular outlet all of sudden wants to keep blowing??
Old 10-07-02, 08:28 PM
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I have to ask....Did you replace the fuse(s) with the same size as the original one that blew?Are you using the correct size fuses for the wire size of the branch circuit ?Is the other outlet that you plugged the micro.into that works,have the same size fuse as the one that blows?What all does the circuit control?(lights,other receptacles in use,etc.) Have you added anything recently to this circuit?
Old 10-08-02, 05:00 AM
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If you changed to another plug and both of these plugs, the one where the fuse blew and the one that you are plugged into now, are located in the kitchen, chances are good that these circuits are of the same size.

Your most likely problem, based on the information you have provided, is a loose connection, either at that receptacle or a receptacle "upstream" of that one. If the connection is loose, with time, it will actually further loosen itself through the process of heating and cooling while it is being used.

If you are going to attempt to look at this yourself, the first thing you need to do is to make sure you know what receptacles are fed by which fuse and turn off all of the power to the receptacles that you wish to work on. Once you have done this, I strongly suggest that you use some type of meter, whether it be some kind of voltage tester or a multimeter and assure that the power is indeed off at those receptacles. Then you can remove them and inspect all of the terminations.

If you don't find anything obvious leave them out and come back here and post what you see so far. Make sure to take a screwdriver and tighten all of the connections, even if they look tight. Don't go crazy though, they just need to be tight, they don't need to be torqued down so hard they will strip.

Good Luck!!!
Old 10-08-02, 06:52 AM
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It can be in the building but can also be in the unit itself. It doesnt always blow the internal fuse but some of the door interlock switches fail,, I dont remember all the details but its a common problem though. We had a couple of them in a commercial kitchen I maintained at one time do that very thing.
Old 10-08-02, 09:28 AM
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could be....

If its a modern kitchen you would have two circuits for appliances. It may be that the original circuit was overloaded. By plugging the microwave into another plug, you may be on a different circuit.
Old 10-08-02, 09:14 PM
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Sparks, have you ever seen a loose connection blow a fuse/circuit breaker? (With the exeption of an afci)
Old 10-09-02, 09:10 AM
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Red face Sure have!!!


Yes, I have seen loose connection cause a fuse to blow or a circuit breaker to trip!!!

The loose connection causes excess current on the circuit when a load is placed on the circuit. If there were a loose connection at the receptacle where the microwave was plugged in, or for that matter at another receptacle upstream from that one, it can cause the breaker to see more ampereage than the microwave actually takes.

Anytime a loose connection exists of any kind, the ampereage of that circuit will be higher than it should be.

I have been on numerous service calls where this has happened.
Old 10-09-02, 11:06 AM
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I'm not quite sure I understand how a loose connection can increase amperage. A loose connection is higher resistance than a good connection, and higher resistance should act to lower the amperage.

Maybe something else going on here? Perhaps the connection became so loose that the wire shorted to ground?

The original poster's problem sounds like a simple overload to me. I suspect that somebody plugged something else in somewhere on this circuit. Or maybe usage patterns changed such that two appliances are in use together when they didn't used to be. Or somebody changed 60-watt bulbs to 100-watt bulbs?

We also don't have the original poster's definition of "blowing the fuse of the outlet". Different people can mean several different things by this same expression.

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