Current transformer (CT) accuracy is specified by an accuracy class, with lower numbers indicating higher accuracy, such as 0.1%, 0.2%, 0.5%, 1%, or 3%. The accuracy level defines the maximum permissible error in current measurement under specific conditions. Some classes, denoted with an "S" (e.g., 0.5S), are special classes with stricter requirements for performance at lower currents, often down to 1% or 5% of rated current, whereas standard classes (e.g., 0.5) may only guarantee accuracy from 5% or 10% of the rated current upwards.