This dual power automatic transfer switch is PC level, household power transfer switch. When the normal city power is abnormal,  the back up power works at once, no Interrupt, ensures the continuirty, reliability, and safety of powersupply. Specifications: Type: W2R-2P 110V, W2R-2P 220V, W2R-3P 110V, W2R-3P 220V, W2R-4P 110V, W2R-4P 220V (optional) Material: PC Main color: black'white Item size: 2P: 107 * 96 * 70mm / 4.2 * 3.8 * 2.8in 3P: 125 * 96 * 70mm / 4.9 * 3.8 * 2.8in 4P: 142 * 96 * 70mm / 5.6 * 3.8 * 2.8in Package size: 158 * 140 * 105mm / 6.2 * 5.5 * 4.1in Package weight: 713g / 1.6lb NOTE: The rated voltage of the common and backup powersupply MustIn range 85%-110%, and the current cannot be less than 5A, otherwise the coil will heat up or even spontaneously burn. If your city voltage not stable, please kindly add voltage protectors in system. Packing List: 1 * Automatic Transfer Switch