Schneider Electric Square D Surgelogic and ASCO 400 series surge protective devices (SPDs) incorporate individually fused and thermally protected metal oxide varistors (MOVs). This feature provides superior withstand capability for systems with unstable power, without compromising transient clamping performance. The component level fusing also allows the surge protector to be directly connected to the electrical bus without external overcurrent protection. When connecting via a breaker, which acts as a service disconnect, consult local electrical codes to select the appropriate size based upon the wire gauge to be used. Based upon National Electric Code (NEC), factory recommendations are listed above. For technical support contact SPDTAG@se.com (800) 577-7353.