# Don't put metal in microwaves--what about the rack?? **URL:** \ **Category:** Factual Questions\ **Created:** [February 10, 2005, 6:44pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442 "2005-02-10T18:44:08Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [February 10, 2005, 6:44pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/1 "2005-02-10T18:44:08Z")
If you put metal in a microwave you get arcs, so you’re cautioned against doing that. But my microwave has a metal rack midway between the floor & ceiling. Why doesn’t it arc? ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [February 10, 2005, 6:47pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/2 "2005-02-10T18:47:43Z")
See [here](http://www.gallawa.com/microtech/metal_arc.html) for the answer to that question. 😃 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 10, 2005, 6:48pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/3 "2005-02-10T18:48:53Z")
Arcs only occur when you get large potential differences across a sufficiently small airgap. Also, arcs are more likely to occur at sharp points - smooth, rounded parts tend to exhibit less arcing. Evidently, this rack is designed so as to avoid these conditions. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 10, 2005, 6:57pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/4 "2005-02-10T18:57:05Z")
> [@silenus](#): > > See [here](http://www.gallawa.com/microtech/metal_arc.html) for the answer to that question. 😃 That page made my Firefox freeze up like a deer in headlights. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [February 10, 2005, 6:59pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/5 "2005-02-10T18:59:58Z")
Beakman (From Beakman’s World) once safely put a fork in the microwave. The trick was to be sure it wasn’t touching the sides or bottom. He put it on top of a plastic bowl or something so that it was suspended in the middle of the microwave. ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [February 10, 2005, 7:20pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/6 "2005-02-10T19:20:10Z")
Put a bag of microwave popcorn on the turntable under your metal rack. Let the popcorn pop until it raises the rack and shifts it from the plastic hooks it sits in. Then take the rack and popcorn out of the microwave and try to remove the scorch marks from the sides of the oven. From this “experiment” I performed a few years ago :smack: I concluded that the rack will not arc as long as it is in its correct position. Move the rack, and watch the arcs begin. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [February 10, 2005, 7:20pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/7 "2005-02-10T19:20:23Z")
> [@Q.E.D.](#): > > That page made my Firefox freeze up like a deer in headlights. Funny. Works fine on Windows98. Usually it’s the other way around! 😃 ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [February 10, 2005, 7:45pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/8 "2005-02-10T19:45:36Z")
> [@Q.E.D.](#): > > That page made my Firefox freeze up like a deer in headlights. My copy displays it OK, sans a missing plugin, which turns out to be Apple Quicktime. It would appear that you have the plugin, and your browser is valiantly attempting to play Debussy as a background. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [February 10, 2005, 7:48pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/9 "2005-02-10T19:48:37Z")
> [@yabob](#): > > My copy displays it OK, sans a missing plugin, which turns out to be Apple Quicktime. It would appear that you have the plugin, and your browser is valiantly attempting to play Debussy as a background. I think that’s it, too. I hate Quicktime with a passion. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [February 10, 2005, 8:01pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/10 "2005-02-10T20:01:32Z")
I regularly put silverware in the microwave. If I’m heating up a bowl of something, and occasionally take it out to stir it, I just leave the spoon in while it’s heating instead of finding a place to set a messy spoon on my countertop. Never had a problem. And contrary to what’s widely believed, even if you get arcs from metal, it doesn’t hurt the microwave (unless, like in Cheesesteak’s case, it makes marks on the sides). ---
**Author:** ![wisernow](https://avatars.discourse-cdn.com/v4/letter/w/13edae/32.png) [@wisernow](https://boards.straightdope.com/u/wisernow)\ **Post date:** [February 10, 2005, 9:33pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/11 "2005-02-10T21:33:42Z")
From the link given by **silenus** > [@](#): > > The interior metal walls of a microwave oven cooking cavity are proportioned with the energy output from the magnetron tube. In other words, the physical proportions of the cavity are tuned to the frequency of the energy, thus producing a uniform electromagnetic wave pattern. In the case of the OP’s microwave, the rack midway between the floor and ceiling is included and is a _part_ of the “cavity” and is tuned to the frequency and so no sparks. This is further proven by what **Cheesesteak** has experimented. If the rack is moved from its location, the “tuning” is lost causing sparks. ---
**Author:** ![Bill\_H](https://avatars.discourse-cdn.com/v4/letter/b/a5b964/32.png) [@Bill\_H](https://boards.straightdope.com/u/Bill_H)\ **Post date:** [February 10, 2005, 9:38pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/12 "2005-02-10T21:38:29Z")
From the link from **silenus** : > [@](#): > > Why do some cookbooks suggest the use of tin foil? How can TV dinners be microwaved? What about the use of metal racks? These questions and others will be answered soon… and then > [@](#): > > As of 12/6/97, you are visitor number… Any day now, we should see those answers. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [February 10, 2005, 11:10pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/13 "2005-02-10T23:10:02Z")
> [@CurtC](#): > > I regularly put silverware in the microwave. If I’m heating up a bowl of something, and occasionally take it out to stir it, I just leave the spoon in while it’s heating instead of finding a place to set a messy spoon on my countertop. Never had a problem. > > And contrary to what’s widely believed, even if you get arcs from metal, it doesn’t hurt the microwave (unless, like in Cheesesteak’s case, it makes marks on the sides). Agree. One of the biggest myths is that you shouldn’t put metal in the microwave. Hell, I do it all the time. Besides, the chamber walls are made of metal, aren’t they? But there are a few guidelines: 1. This is obvious, but you shouldn’t encase food in metal. It will reflect the microwaves and won’t get cooked. 2. Do not put metal pieces in the microwave that have high resistance. This would include any metal with a small cross-sectional area (e.g. foil). This is because the microwaves induce electrical currents in the metal, and too much resistance may cause the metal to overheat via I[sup]2[/sup]R. A spoon, for example, is O.K. But foil is not O.K. 3. Never turn on a microwave oven with nothing in it (i.e. without a load). This creates a big mismatch in the waveguide, and a lot of the energy gets reflected back to the magnetron. This is could cause the magnetron to fail. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [February 11, 2005, 4:47am UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/14 "2005-02-11T04:47:58Z")
From the link given by **silenus** > [@](#): > > The interior metal walls of a microwave oven cooking cavity are proportioned with the energy output from the magnetron tube. In other words, the physical proportions of the cavity are tuned to the frequency of the energy, thus producing a uniform electromagnetic wave pattern. I don’t think this is right. For one, all microwaves operate at the exact same frequency, so wouldn’t they all have similar dimensions if it were true? For another thing, the way it’s worded tells me that the person has no idea what he’s talking about. “Proportioned with the energy output from the magnetron tube”??? What the hell does that mean? The microwave designer wants it _not_ to act as a resonant chamber, and puts a spinning metal “stirrer” in there to make sure it doesn’t. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [February 11, 2005, 3:15pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/15 "2005-02-11T15:15:09Z")
> [@CurtC](#): > > From the link given by **silenus** I don’t think this is right. For one, all microwaves operate at the exact same frequency, so wouldn’t they all have similar dimensions if it were true? For another thing, the way it’s worded tells me that the person has no idea what he’s talking about. “Proportioned with the energy output from the magnetron tube”??? What the hell does that mean? The microwave designer wants it _not_ to act as a resonant chamber, and puts a spinning metal “stirrer” in there to make sure it doesn’t. I agree. I think [this](http://www.physics.sfsu.edu/~senglish/research/microwaves_are_pretty_cool.htm) page has a better explanation. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [February 11, 2005, 3:30pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/16 "2005-02-11T15:30:15Z")
Withing reason, it doesn’t matter how much arcing occurs in the chamber. The difficult comes from reflecting microwaves back into the output of the power tube - magnetron, klystron or whatever. Such devices are specified with a maximum standing wave allowed in the output so as not to damage the device. So the chamber with all of its metal parts is constructed and the power tube output is located in the chamber so as to keep the standing waves in the tube output at a safe level. Things that absorb energy, like food, don’t cause any problems because they don’t increase the standing waves in the tube output. However metal things reflect energy which changes the distribution of energy in the chamber so as to possibly increase the standing wave in the tube. Metal objects in the chamber won’t _always_ cause power tube damage but there is the strong possibility that they will do so and therfore should be avoided. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [February 11, 2005, 4:42pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/17 "2005-02-11T16:42:15Z")
> [@David Simmons](#): > > Things that absorb energy, like food, don’t cause any problems because they don’t increase the standing waves in the tube output. However metal things reflect energy which changes the distribution of energy in the chamber so as to possibly increase the standing wave in the tube. Metal objects in the chamber won’t _always_ cause power tube damage but there is the strong possibility that they will do so and therfore should be avoided. I’m not a microwave engineer, but I guess I disagree with some of this. First of all, I’m pretty sure that putting food (or whatever) in the microwave will _reduce_ the SWR. The energy has to go somewhere, and if food is absorbing the energy, then I figure the SWR must decrease (which is a good thing). A good analogy is a coax cable terminated with a short vs. a coax cable terminated with a resistor. The short represents a microwave with nothing in it, and the resistor represents food. The SWR with the resistor will be less than the SWR with the short. With the above comments in mind, I do not believe putting metal in the microwave will hurt anything as long as: 1. There’s also a load (e.g. food) in the chamber. 2. The metal does not have high resistance (else the metal could overheat). ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [February 11, 2005, 7:04pm UTC](https://boards.straightdope.com/t/dont-put-metal-in-microwaves-what-about-the-rack/289442/18 "2005-02-11T19:04:41Z")
> [@Crafter\_Man](#): > > > [@David Simmons](#): > > > > **Things that absorb energy, like food, don’t cause any problems because they don’t increase the standing waves in the tube output.** [bold added] However metal things reflect energy which changes the distribution of energy in the chamber so as to possibly increase the standing wave in the tube. Metal objects in the chamber won’t always cause power tube damage but there is the strong possibility that they will do so and therfore should be avoided. > > I’m not a microwave engineer, but I guess I disagree with some of this. > > First of all, I’m pretty sure that putting food (or whatever) in the microwave will _reduce_ the SWR. **The energy has to go somewhere, and if food is absorbing the energy, then I figure the SWR must decrease (which is a good thing).** [bold added] A good analogy is a coax cable terminated with a short vs. a coax cable terminated with a resistor. The short represents a microwave with nothing in it, and the resistor represents food. The SWR with the resistor will be less than the SWR with the short. > > With the above comments in mind, I do not believe putting metal in the microwave will hurt anything as long as: > > 1. There’s also a load (e.g. food) in the chamber. > 2. The metal does not have high resistance (else the metal could overheat). Am I writing this in Sanskrit or some other obscure tongue? What is the essential difference between the sentences in **bold** above?