Iec61869-2 -

: It specifies limits for ratio error and phase displacement across various classes (e.g., 0.1, 0.2, 0.5, 1, 3, and 5).

IEC 61869-2 applies to current transformers intended for use with electrical measuring instruments and electrical protective devices at frequencies between 15 Hz and 100 Hz (typically 50 Hz or 60 Hz). iec61869-2