Its 24.4V minimum breakdown voltage means it starts conducting just above the rail's normal tolerance, and the 48.3V maximum clamping voltage at the peak pulse current of 207A (8/20µs waveform) defines the upper bound the protected circuit sees during a surge.
Unidirectional — one rail, one polarity
This is a unidirectional device, meaning it protects a single polarity rail (e.g., a positive DC bus referenced to ground). For AC lines or bipolar supplies, you would need a bidirectional variant from the same SMCJ family. The single-channel construction is the standard choice for DC power inputs, signal lines, and low-voltage DC buses where the transient is unipolar.