金属氧化物避雷器MOA的核心元件是金属氧化物电阻片（MOR），他的主要成分是氧化锌，约占90%。正常时工作在小电流区，在工作电压下呈现很大的电阻，流过MOA的电流很小，约0.1~0.2mA，可以近似认为是断开的。当系统产生过电压时，比如雷电入侵，在过电压作用下MOA呈现低电阻，对地导通，将过电压泄放，只有很小的残压，这样就可以保护其周围的设备不受过电压的危害。
The core element of the metal oxide arrester MOA is the metal oxide resistor (MOR), the main component of which is Zinc Oxide, which accounts for about 90%. Normally, it works in a small current area, and presents a great resistance at working voltage. The current flowing through MOA is very small, about 0.1~0.2mA, which can be regarded as disconnected approximately. When the system generates overvoltage, such as lightning invasion, under the action of overvoltage, MOA presents low resistance, which leads to overvoltage, and only a small residual voltage is released. This way, it can protect the equipment around it from being damaged by voltage.