Why Does Microwave Spark? (7 Real Reasons)

If you have been trying to cook using your microwave oven and have suddenly started to notice sparks inside then it is a justifiable concern.

There are several things that cause microwave sparking but the most common of them is metal. Any small piece of metal left inside the microwave while it is turned on will cause sparking.

As the name will tell you, a microwave oven uses electromagnetic microwaves to cook and heat food, unlike traditional ovens that use convection technology. So any foreign material that gets in the way of this electromagnetic wave field and which is not a good conductor of it will cause microwave sparks.

But as already mentioned, metal is just one reason behind why this happens although it is common as well. There are several other reasons.

Is It Normal For A Microwave To Spark?

No, it is not normal for a microwave to spark.

Most will start panicking once they see this happening and quite naturally so because not all people can be expected to know the ins and outs of a microwave. But while it is not normal, it is not uncommon too.

This happens quite often and it is the device’s way of telling you that something is hindering its smooth functioning. This does not mean that the microwave has gone bad or needs professional repairs and such.

Why Does Microwave Spark?

Why Does Microwave Spark

Here are some of the most common reasons that causes a microwave to spark.

Metal inside the Microwave

As mentioned once before, metal is the most frequent cause of a microwave sparking inside. Every microwave manual or user’s guide mandatorily mentions that any metal no matter how small must not be put inside a switched-on microwave.

This is because metal is not a good conductor of electromagnetic waves and when they come into contact with each other, the waves are changed into electricity thus causing the sparks.

The metal we are talking about here may be a small coffee spoon or a scrap of tin foil. No matter what, you should always avoid putting metal inside the microwave.

Broken or Dirty Waveguide Cover

The waveguide cover in most microwaves is a small square panel that can be seen on one side wall of the interior. This is an essential portion of the microwave as it is responsible for transferring the power from the magnetron and distributing the energy to heat or cook food.

This cover also prevents any food or foreign particles from entering the magnetron. Thus it is natural for grease and oil from certain foods to stick and solidify on the waveguide cover, which if not cleaned regularly leads to sparking inside the microwave.

A broken waveguide cover is more dangerous than a dirty one because if the cover is damaged it will not be able to protect the magnetron and electronics of the microwave from getting covered in oil and grease and maybe even splashes from the food being cooked inside. This will not only cause sparks in a microwave but also might cause a short circuit and breakdown of the machine.

The best course of action is to remove the broken cover and get it replaced by a new one as soon as possible.

Burnt out Diode

Every microwave contains high-voltage diodes inside to assist the magnetron in cooking food by supplying power to it.

The diode in a microwave is seldom the cause for a microwave oven spark but still cannot be completely ruled out as a probable cause.

Surges in current may cause these high voltage diodes to get shorted or burned and if that is indeed the case then your microwave will soon stop functioning after the diode gives out. The diode basically helps the magnetron to create waves and cook the food and that is the whole point of a microwave.

If the diode stops working, it will need immediate replacement.

A Worn Out Rack Support

If your microwave comes with a cooking rack then it has some holders which will secure it in place when being used inside the microwave. Now the thing is, although metal is forbidden inside the microwave these holders are still made of metal.

To avoid parking and interior damage, this metal is then coerced well with protective and good-quality plastic.

Over time and with usage, the sheath of plastic may wear off thus exposing the metal underneath. We already know metal causes a microwave to spark and this metal is no different.

Broken Microwave Stirrer

The purpose of a stirrer inside a microwave is to ensure that the food heats evenly inside the microwave. So if the stirrer is faulty then the heat will be concentrated in one space instead of being spread properly.

The tell-tale sign of a faulty stirrer is when the food is not equally hot in all the portions and retains extreme heat in one portion.

A broken stirrer belt or a broken drive motor or both may be the reason why this is happening. In any case, it has nothing to do with the crucial electronics of a microwave and thus is not an immediate cause of panic. But you should get it fixed anyway because sparks inside the microwave are never a good thing.


Although metal is forbidden inside the microwave, the insides are still made from it. Wondering how that works? Well, the interior is covered with a layer of protective paint to cover the metal and not let it get exposed to the microwaves.

Heat is a corrosive agent and thus in time the paint may start to wear off at places and fall off in patches thus exposing the metal underneath it. This may cause sparking. The easiest solution to this is to touch up the area or areas where the paint has chipped off with some paint that is suitable to be used inside a microwave.

Failing Magnetron

The magnetron of a microwave is responsible for creating the electromagnetic waves that heat the food.

If you notice that the food is not being heated properly and there is a distinct buzzing or humming sound coming from the microwave, even more than the usual amount, then chances are the magnetron is failing and needs a replacement.

This may also cause sparking inside the microwave. If such is the case with your microwave then disconnect it immediately from any electric socket and call for professional help.

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Does Arcing Damage A Microwave?

Does Arcing Damage A Microwave

It depends. If your microwave is okay after you have removed any metal infestation then it is definitely not damaged. If however, the spark continues to occur every time you turn it on even after removing all exposed metal, then the microwave may have taken a blow.

The tell-tale signs of a damaged microwave is food not being properly heated, loud humming sound and an unpleasant smell that comes out after the sparking occurs at a slightly lower voltage than usual.

The microwave may still work after that, but ask yourself, should you risk it?

What Happens When A Microwave Arcs?

The occurrence of sparks inside a microwave, known as arcing, happens when charged particles build-up and produce a concentrated electric field at the edge of a metal object.

Simply put, what happens is when the electromagnetic waves emitted from the magnetron hit a metal instead of food, it causes sparks. 

While it does not immediately damage the microwave, arcing may cause the food to get splattered onto the waveguide cover and we have already discussed what happens when the waveguide gets dirty or damaged- it leaves the magnetron vulnerable to food splashes and eventually more sparking.

How Do I Stop My Microwave From Sparking?

If, whenever you turn on your microwave it is sparking then you have to first identify the cause of it. However, it is understandable if you are unable to. Call a mechanic and let them handle it for you.

That said, the metal infestation is mostly why a microwave oven sparks so before you give the mechanic a call you can check thoroughly if any metal scraps have been left inside the microwave chamber or if the rack holder has worn out exposing the metal underneath thus causing the sparks.

Removing the cooking rack and the holder will not affect your cooking and you can use the tray beneath unless you get the rack replaced.

However, fixing microwave arcing, although can be done at home by yourself, should not be attempted unless you are familiar with handling electronic devices and have a basic idea about microwave parts.

Is It Safe To Use A Microwave After It Sparks?

Is It Safe To Use A Microwave After It Sparks

This depends on why the microwave is sparking. If it is because of a metal infestation, then simply removing the metal from the microwave will stop the sparks and make it perfectly safe to use again.

However, if the sparking is being caused by a broken guide cover or a broken diode then it is best to not use the microwave until the parts are all fixed or replaced.

This is because the guide cover also protects the internal magnetron and electronics of the microwave and those parts if exposed to splashes of liquid food, or grease and oil may get damaged leading to a much bigger fault in the divide.

Similarly, the diode plays an important role in surging the power needed by the magnetron to create waves and cook food.

A microwave with a failing magnetron should not be ideally used because it leaves a carbon trail deep inside the magnetron core which is very conductive and may result in a low voltage spark the next time it happens.

These faults cannot be dealt with as simply as removing metal infestation and it is best to seek professional help.

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Final Thoughts

If you notice sparking inside your microwave, the first thing you should do is not panic and simply turn the unit off and disconnect it from the electrical socket. By doing that, you are safeguarding the microwave from any possibility of an electric short-circuit.

The next step is to read this guide and try to find out the cause behind those sparks. Call for professional help if required. 

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