What the 1.5KE300CA/B protects and how to read its ratings
The 256 V reverse standoff voltage means the device does not conduct leakage current below that rail — it sits across a 240 VAC or 256 VDC bus and stays invisible until a transient exceeds the 285 V minimum breakdown threshold. When the transient hits, the diode clamps at 414 V maximum while shunting 3.7 A peak pulse current. That 414 V ceiling is the voltage the downstream circuitry must survive — if your DC bus capacitors or downstream regulators are rated below that, the TVS may not save them. The bidirectional configuration means a single DO-201 part clamps both polarities — handy for AC lines or floating DC rails where the transient polarity is unknown. No power line protection built in (the 'Power Line Protection' flag is No), so this is for signal or low-power DC bus protection, not mains AC primary-side clamping.
Package and board-fit — through-hole DO-201 axial
Housed in a DO-201AA (DO-27) axial leaded package, the 1.5KE300CA/B mounts through-hole. The axial leads require a hole pitch matching the body length — typically 8.5 mm lead spacing on the PCB. The DO-201 body diameter is about 5.3 mm; plan for clearance to adjacent components if you are retrofitting onto a tight board. The junction temperature rating is the one that governs derating: at 150°C ambient the peak pulse power must be derated per the manufacturer's curve, but for most board-level repairs at room temperature you get the full 1500 W.
Sourcing and lifecycle — active, no end-of-life concern
No stock-holding claim; the part is procured through independent distribution channels with full traceability.