At input side, there will be a large transient inrush current during the power on of an SPS. The inrush current is usually of 20~70A based on the design of SPS, which will last for 1/2~1cycle of AC input (ex. 1/120~1/60 seconds for 60Hz AC source). Every breaker or fuse will actually have its own time-current (V-I) characteristic curve. Users can choose a breaker or fuse which has a rated current just over input current of SPS and check whether the V-I curve of the breaker or fuse can withstand the high inrush current from the SPS with a maximum duration of 1 cycle of AC input (e.g. 1/60 second).