This is a ProSurge Type 2CA SPD 3-Pole AC Power DIN-Rail Surge Protective Device. Its part number is SP420C/3P-S. This item comes as pictured and does not include any additional parts or accessories.
Specifications:
Manufacturer: ProSurge
Part Number: SP420C/3P-S
Poles: 3
Max. Discharge Current, Imax (8/20μs) (kA): 50
Nominal Discharge Current, In (8/20μs) (kA): 20
Nominal Voltage (VAC): 347
Max. Continuous Operating Voltage MCOV (VAC) L-G: 420