The optimal solution in most cases is the Power Perfect Box Wire-In. It provides maximum protection for all circuits on all phases right at the breaker panel. It also provides additional protection and filtering with its Phase-to-Phase filtering capabilities. The Power Perfect Box Plug-In will definitely protect the circuit on which it is installed and other circuits on the same phase but it doesn’t protect as optimally as the Power Perfect Box Wire-In. It also only filters Phase-to-Neutral. The Power Perfect Box Plug-Ins may be better for lower EMI readings in some situations.