Microwave Oven

Why Does Metal Spark in a Microwave? | How Concerning is It?

A mug in a microwave
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You've probably experienced a spectacular light show of sparks when warming your favorite cup of coffee. I experienced it when I left a fork and proceeded to cook my bowl of oats. I immediately slipped into panic mode! But why does metal spark in a microwave?

Well, you must have heard that putting metal in a microwave is a bad idea. A combination of metal and electromagnetic waves ends in sparks or sometimes fire.

But do all metals spark? What happens when the microwave spark? Do sparking harm the microwave? A lot of questions must be running through your mind. Do not worry. This informative article will address all your queries.

Metalic microwaave

How Does a Microwave Work?

Microwaves ovens came into our lives in the 1970s. Since then, everyone has been wondering why metal sparks in a microwave. The magical metal box(as referred then) brought the much-needed convenience of cooking and warming delicious meals in minutes!

But what puzzled many was the metal box's ability to rotate as it warms food and not anything else around it. The oven produces electromagnetic waves through an electron tube known as a magnetron. The interior of the microwave comprises metal. The metal surfaces reflect the microwaves, and later, the food absorbs them.


Foods with high water content cook fast because they absorb energy from the waves. Note, electrons change to heat before being absorbed by foods. The reaction does not necessarily make your meal contaminated. You can enjoy your healthy and delicious foods right from the microwave.
Metal dishes


Is It Bad if Your Microwave Sparks?

Microwave sparking might cause panic, but mostly, it is nothing serious. However, in some rare cases, microwave sparking due to broken electronics can result in electrocution.

To avoid such situations, turn off the microwave immediately when it starts sparking. Continuous sparking can cause permanent damages to the microwave's interior.

Does Metal Always Spark in the Microwave?

Microwaves, like all radio waves, are made up of electric and magnetic fields. A microwave pushes electrons back and forth across whatever metal it touches. The movements are a result of the forces put on charged particles by an electric field.

These back-and-forth movements of electrons through the microwave walls allow the reflection of the microwave. The waves are kept inside the oven. So, if a spoon is present when a cup of coffee is heated in a microwave, electrons flow back and forth through the spoon.

If the charges are allowed to reach their maximum potential, the charge motion causes no problem. Also, the cooking continues undisrupted if the spoon can sustain the charge flow at its edge. The spoon's edges should be smooth to avoid sparking.

Because electrons are more likely to depart a metal object at a sharp point, avoiding sharp points is critical. Most spoons are smooth enough to prevent sparks. A sharp piece of foil, or a twist tie, or a fork, on the other hand, may begin to spark electrons into the air once a concentrated electric field piles up at the edge.

A white plate in a microwave

Does Metal in the Microwave Damage It?

A microwave oven generates heat after water molecules in your food interact with the microwaves. Water changes to steam as food heats up and releases energy. On the other hand, the molecules in metal heat up but have nowhere to go. On a side note, a microwave with 900 watts would suffice for basic heating, while for more demanding cooking one should opt for a higher-powered oven.

Metal heats up quickly, and if action is not taken immediately, it starts parking and eventually catches fire. The metal objects must be good conductors of electricity to avoid overheating. Fairly thick metal substances (like most spoons) do not overheat as the microwave's mild currents leave little energy within them.

A thin twist tie or a small piece of aluminum foil, on the other hand, may quickly spark, igniting any soft material around. However, the microwave may be destroyed beyond repair if there is nothing to absorb the microwaves and as such you'll have to look for a new one. Luckily, we already shared our thoughts on microwaves under 200 dollars. At the same time, though, because most sought-for microwaves come around this price range, you could get a great microwave for less than150 bucks.

Why Don't Interior Metals of a Microwave Spark?

Experts and microwave manuals are against putting metal in a microwave oven. But have you wondered why microwave interiors are made of metallic material but pose no harm? Well, the oven walls, like a spoon, are good conductors of electricity and have no sharp points.


While electrons flow back and forth in these barriers, they reflect microwaves without becoming extremely heated or producing sparks. The microwave light bulb is always outside the cooking chamber. The reason behind it is that it contains metallic particles that cause problems inside a microwave.
Melted chocolade in a metal bowl


What Causes the Aluminum to Spark in a Microwave?

Thick metallic pieces, like microwave walls, reflect electromagnetic waves. Typically, thick metals withstand currents from electric fields without any problem. But it is a different story with thin metallic parts such as aluminum foils.

Aluminum foils and other thin metals are swapped by the currents and quickly heat up. The waves move so fast, and within minutes, they can cause a fire. Furthermore, if the foil is wrinkled to the point that it creates sharp edges, the electrical current traveling through it will cause sparks.

For instance, an aluminum foil placed in a flat circle may not spark, but it will emit a shower of sparks once folded into a ball.

What Are Other Common Reasons for a Sparking Microwave?

Metallic objects in a microwave are the leading cause of sparking. But there are several other reasons.

1. Broken microwave waveguide cover

A waveguide cover allows waves through the food, thus facilitating healing. The waveguide cover also protects the magnetron from food particles. In case the cover is broken, steam and certain substances may accumulate in the electronics.

Therefore, cleaning the cover first as a blockage can result in sparking. If the sparking continues even after washing, contact an electrician.

Metal plates with spoons


2. Damaged rack support

Some electromagnetic waves have well-designed metal racks that offer additional support when cooking more than one plate. If the paint is worn out, the metal is exposed to the microwaves resulting in sparking. So, a technician will advise whether to repaint or replace it with a new one. Speaking of new microwaves, though, a technician would probably not advise you to go for a form over function, but new retro-designed ovens will try to appeal to your aesthetic side.

3. A faulty diode

A diode is one of the most vital parts of a microwave. The diode generates, detects, and switches microwave signals. Because of its critical function, the diode is regularly used, exposing it to a lot of wear and tear.

Normal wear and tear can result in sparking and little heat production. On the other hand, a worn-out and shorted diode may result in the emission of loud humming noise.

If you experience such problems, consult a technician. Note, all diodes in microwaves are of high voltage hence require professional replacement. To prolong the lifespan of the diode, always use the recommended switches and power source each time you use the microwave.

4. Incompatible cookware

For the cookware to be microwave compatible, electromagnetic radiation should be able to pass through. To test if your cookware is microwave compatible, place a container full of water on top of the new container; microwave for one minute.

If the container comes out hot, it fails the test, and you should never use it in your microwave.

Microwave-compatible cookware does not heat up.

5. Microwaved grapes

Grapes have high water content. Grape water traps enough energy emitted by the microwave. Once accumulated, the electrolytes are charged. The electrolytes flow from one grape to another. As a result, the surrounding air is supercharged into bright plasma, causing eventually sparks in the oven, which could lead to serious consequences as explained in this post on the matter.

Woman looking in the microwave on a counter


The Final Word

As appliances go, microwaves are vital in our homes; they make cooking fun and fast though convection microwave ovens make it even faster. Nonetheless, almost every homestead has experienced a sparking microwave. Although it might be harmful, we must understand what triggers the sparks.

Putting metallic objects, especially thin and poor conductors of electricity, can harm your microwave. Similarly, other reasons such as a faulty diode, damaged rack support, and broken waveguide cover can cause microwave sparks.

Although one can solve the sparking problem independently, it is advisable to consult a technician if the faulty parts need replacement. So, avoid metallic objects in your microwave and prolong its lifespan.

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