Clamping voltage and breakdown window
The 1.5KE170C-E3/54: The 138 V standoff rating means the diode draws negligible leakage below that level, making it suitable for 120–130 V nominal rails where the transient margin is tight. The bidirectional configuration (single device, two back-to-back Zeners in one die) protects both polarities — no need to orient the part on the board.
Obsolete — sourced through independent channels
Vishay has marked the 1.5KE170C-/54 as obsolete. No pin-compatible direct replacement is documented; a parametric search on 1500 W bidirectional TVS in DO-201AA with a 138 V standoff will yield functional alternatives, but each requires board-level verification of the clamping voltage and package footprint.