What the ratings mean for your circuit
The 1.5SMC18C: The 15.3 V reverse standoff means it won't leak or conduct at normal rail voltage up to that level; the breakdown starts at 16.2 V min, and clamping is limited to 26.46 V at 60.3 A peak pulse current.
Housed in a DO-214AB (SMC) surface-mount package — the same footprint as the SMCJ series. The copper pad area under the cathode tab sets the thermal resistance; a solid ground-plane pour under the device improves peak-pulse energy handling. Supplied on Tape & Reel — standard for pick-and-place.