What the 400W rating means for your board
The SMAJ85CA-13: For a 24Vdc rail with a 85V standoff, the clamp hits 137V at 2.9A peak pulse current, so downstream parts see a hard ceiling instead of a ramp.
DO-214AC (SMA) surface-mount package, supplied on Tape & Reel. The SMA footprint is standard — two pads, no exposed paddle, so a two-layer board handles the thermal dissipation if the copper pour is generous. Bidirectional channel means one part covers both polarities; no need to worry about orientation for reverse-voltage events.