How Come the Metal Shelf in a Microwave Doesn't Spark?

The Type of Heat

• Modern microwaves that use a combination of microwave and convection heat are often the ones that come with a metal shelf. Because convection heat doesn't use the magnetron, the metal shelf doesn't arc during cooking. Switching to microwave mode and leaving the shelf in place will cause the metal to arc.

How Convection Cooking Works

• Convection cooking works the same way as a conventional oven: an electric heating element warms air to between 200 and 400 degrees Fahrenheit while a fan circulates it past the food. This type of heat produces crisper, oven-like results when compared with microwave heat. Microwaves are better at heating food from the core outward than conventional ovens.

Using the Metal Shelf

• The metal shelf should only be used when using convection, bake, broil, toast or warming modes. Take out the shelf before using the oven's microwave function, placing your food on the turntable instead.

Avoiding Arcing

• Always remove the metal shelf from the oven before using the microwave cooking mode. Don't heat metal foil, metal twist ties, poultry pins, gold or reflective rimmed dishes and some types of recycled paper towels that contain small metal pieces. Stop the microwave immediately if you notice arcing.