The paint on the interior of the microwave might be chipped. It would have the same effect on all metals. To use a rack in a solo oven, begin by consulting the user's manual. If the unit came with a metal rack, be certain that the rack is installed properly on all four of . If the paint is chipped, the interior metal will be exposed, causing the microwave to spark or arc. Earn 10 reputation in order to answer this question. Sparking in the microwave is a common thing. That's why microwaves can have metal racks which are designed so as not to spark in the microwave oven. ARCING OR SPARKING – METAL RACK . My guess would be that's just the way its engineered. If there are any damaged spots, touch them up with microwave … the plastic support brackets in the case of over-the-range models. Why can there be a metal rack in a microwave, but we can’t put anything metal in it? If it's grounded, energy won't build up and you won't have sparks. $\endgroup$ – Peter Shor Aug 12 '13 at 1:52. add a comment | Highly active question. You’re right, the rack is metal. It isn't because of the type of metal, I don't think. Check the interior of the microwave for any spots where the paint has chipped away. The reputation requirement helps protect this question from spam and non-answer activity. Maybe when the rack is in the microwave, it is grounded. Or the rack doesen't have ANY sharp points and perhaps is also grounded. Liquid spilled inside the appliance of a microwave or grease accumulating on the interior sides of your microwave is believed to cause sparking in the internal cavity. Arcing or Sparking – Metal rack issue Cause Did the microwave oven come with a metal rack? If not, sparking … There are two types of metal rack in a microwave. I don’t think there is a specific rule preventing “anything metal”. It is specifically designed so that the gaps between the rods of the rack are large enough to prevent sparking and to allow the microwaves to pass through.