Hobbies And Interests
Description
MOVs come in a few different varieties. Those protecting consumer appliances and power equipment are round, flat, coin-sized devices painted in glossy colors, such as black, blue or yellow. Larger MOVs protect industrial equipment. Smaller ones are also available to handle surges in sensitive low-voltage electronics. All MOVs have two wires, terminals or connectors for wiring them into a circuit.
Action
Inside an MOV, a layer of zinc or other metal oxides produces a high electrical resistance at normal voltages. At high resistance, the device is in effect "invisible" to the circuit in which it is wired. When voltage suddenly increases, as in a surge, its resistance drops and the MOV absorbs the surge's energy, turning it into heat. As long as the surge's energy is within the MOV's rating, it warms for a few minutes, sending its heat into the immediate environment before cooling to room temperature.
Speed
The MOV's resistance drops in a few billionths of a second. This is fast enough that it prevents a voltage surge from moving past it into more sensitive circuits. Though the material in the MOV reacts within trillionths of a second, electromagnetic effects in the device's leads slow the action slightly.
Limitations
The MOV is a simple, inexpensive device. Each one has a rating for the maximum surge energy it can safely handle. Extremely strong surges cause it to burn or burst, destroying the device. It protects only against voltage surges; current surges, brownouts and blackouts require more elaborate protection, as from an uninterruptible power supply, or UPS.