The BK/S501-250-R is a fast-acting ceramic tube fuse in the S501 series, designed for circuit protection in AC applications. It features a 5mm x 20mm physical size with nickel brass endcap construction and is rated for 250 mA at 250 VAC with an interrupting rating of 1500 A. The fuse exhibits a typical melting I²t of 0.027 A²Sec and a typical voltage drop of 1300 mV, providing reliable protection with minimal circuit impact. It is designed to IEC 60127-2 standards and carries multiple agency approvals including UL, CSA, cURus, SEMKO, VDE, IMQ, and CCC recognition. The -R designation indicates RoHS 2002/95/EC compliance, making it suitable for modern electronic equipment and industrial control systems requiring environmentally compliant protection devices.