SPD (Surge Protective Device or called surge arrester) is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to regulate the voltage supplied to an electric device by either blocking or by shorting to ground voltages above a safe threshold. We have spark gap, MOV and Spark tube type for different protection area. 

For the whole building lighting protection, 30kA-60kA, 40kA-80kA, 50-100kA, are available, however, 30kA-60kA is the most common one. As we know, one building have two unita, one is A, the other one is B, for A or B, surge arrester 20/40kA will be your best selection. What's more, we also can provide the one such as surge arrester 5-10kA,especially 10-20kA to strongly protect the single room, 5-10kA to protect a single unit electric device.