EOL status — this part has a last-time-buy
The 1.5KE51C-B is marked Obsolete by Littelfuse, which means the manufacturer has closed the last-time-buy window and no longer produces it. Any available stock is what remains in the distribution channel or surplus market.
What the 1.5kW rating means for the circuit
The clamping voltage of 73.61V at 21.7A peak pulse current tells you the maximum voltage the protected node sees during that event.
The DO-201AA (DO-27) axial-lead package is a through-hole format — the leads insert into plated holes on a PCB or terminate into a terminal block. The 1.5KE series uses this same body across all voltage variants, so the footprint is standard across the family. The wide Tj envelope suits outdoor or engine-bay transient protection where ambient heat adds to the self-heating from the surge.