What the 1500W rating means for your rail
The 1.5KE24CA-TP is a 1500W bidirectional Zener TVS diode in a through-hole DO-201AE axial package. The 20.5V reverse standoff voltage is the maximum DC voltage the TVS sees in normal operation without conducting leakage current. On a 24V bus, this means the part sits below the rail voltage and only starts to clamp when a transient pushes the line above 22.8V (minimum breakdown,). The 33.2V clamping voltage at the peak pulse current is the absolute maximum voltage the downstream silicon sees during the event — that 33.2V ceiling is what protects a 36V-rated DC-DC converter input or a 40V MOSFET drain.
Bidirectional — one part, both polarities
On an AC signal line or a DC rail that can see reverse polarity faults, you do not need two back-to-back unidirectional TVS diodes — the 1.5KE24CA-TP handles both directions in one axial body.