Product Description Perko's 8501 Series battery selector switches are among the most popular battery switches ever produced. Their use of the traditional Perko bolt circle makes for easy installation, whether new or as a replacement. These switches can be mounted in numerous locations. And as ignition protected switches, they can be installed in the engine rooms of gasoline powered boats. In addition to doing everything a battery disconnect switch does, battery selector switches permit battery selection (of two or more batteries) for specific purposes including starting engines, running accessories or even recharging. They allow for the use of one or more batteries in systems with one or more engines and facilitate putting batteries in parallel for emergency starting when one or both batteries are substantially discharged. Perko battery switches are designed for surface mounting. Standard duty switches have a bright red polycarbonate housing for safety with a large easy-to-turn black knob. The housing of the heavy duty switches are red fiber-reinforced polycarbonate. Selector switches are designed with a "make before break" feature. This allows switching between the "1", the "ALL" and the "2" positions while the engine is running. Models with an "Alternator Field Disconnect" feature offer protection for Non-Unitized Alternators should the switch accidentally be turned to the "OFF" position with the engine running. Versions of the 8501 Series switches offer additional features such as alternator disconnect and key lock security. The 90° rotation feature allows users to feel the switches' position in no light situations and the classic shape of the knob makes it easy to turn. High conductivity studs are long enough to handle more than 1 cable and strong enough for torque needed for secure connections. Optional spacer ring (PN 0462DP0RED) allows for the use of larger cables. Like all Perko products, these time-proven switches are made in the USA. Protected by US Patents: 260,637 - 4,280,028 - 4,424,424 Technical Information Diameter: 5-1/4 square inches Depth: 2-5/8" Polycarbonate Body with Brass Terminals Ignition Protected For use with 6 to 50 Volt Marine Electrical Systems Capacity - 250 AMPS Continuous, 360 AMPS 5 Mins. Intermittent Terminal Stud Size: 3/8" When used with Non-Unitized Alternators, these models will interrupt the field current (reducing the possibility of damage) if turned "OFF" with the engine running.