Clamping parameters and circuit protection envelope
The 1.5KE20AHE3/51: The 10/1000 µs pulse condition is the industry-standard TVS test waveform; the 54.2 A figure tells you the diode can shunt that current without exceeding its thermal limit for that pulse duration.
Through-hole mounting in a DO-201AA (DO-27) axial package. The 1.5KE package code matches the standard TransZorb outline; the axial leads require a hole diameter of about 1.1 mm on the PCB. No power line protection is built in — this is a standalone transient suppressor, not a filtered TVS array.
Vishay has marked the 1.5KE20AHE3/51 as obsolete. No pin-compatible direct replacement is documented; a parametric search for a 1.5 kW, 17.1 V standoff, unidirectional TVS in DO-201AA will yield functional alternatives, but each requires BOM-level verification of the clamping voltage and pulse current profile.