A current Transformer(CT) is an electric device that produces an Alternative Cureent(AC) in its secondary which is proportional to the AC in its primary.Here is 5A in Primary and 2.5mA in secondary.
Typically used for relay protection and energy meter
Ratio Difference non-linearity:+/-0.1%
Phase difference non-linearity:+/-5'
Linear Range:5%-2000%
Frequency:50-60Hz
Insulation Resistance:100M ohm@500Vdc
Dielectric strength: 3000V r.m.s (2mA @ 1minutes)