Breakdown, clamp, and pulse current — the three numbers that size the protection
The 1.5KE22A-E3/73: The 18.8 V reverse standoff means the diode draws negligible leakage below the normal rail voltage — it stays invisible to the circuit until a transient pushes past 20.9 V, at which point the avalanche breakdown conducts and the clamp limits the peak to 30.6 V. Rated for 49 A of peak pulse current at the standard 10/1000 µs test waveform, this part handles the energy of a typical inductive-load dump or lightning-induced surge on a 24 V nominal bus without exceeding the junction temperature ceiling of 175 °C. The single unidirectional channel protects one signal or power rail; for bipolar or AC-coupled lines, two devices back-to-back or a bidirectional variant would be needed.
Through-hole axial package — board-level integration
The DO-201AA (DO-27) axial-lead package is a through-hole form factor suited for point-to-point wiring, terminal blocks, or PCB mounting with lead bending — the body diameter is roughly 5.3 mm and the lead diameter 1.3 mm, allowing it to carry the 49 A pulse without trace lift-off on a standard 2 oz copper board.