The accuracy grade of a current transformer is a key indicator of the accuracy of its measurement or protection performance. Different grades correspond to different tolerances, and the selection should be based on the specific application (metering, measurement, protection). The following is a classification of common accuracy grades and detailed descriptions:
I. Accuracy Grades by Application
1. Accuracy Grades for Metering Current Transformers
Used for energy metering (electricity bill settlement), they require high accuracy and a strict tolerance. Common grades:

Grade 0.1: At rated current, the ratio error (current ratio error) is ≤±0.1%, and the phase error (phase error) is ≤±5 minutes. This grade is suitable for high-precision metering scenarios (such as gateway metering and large power plants).

Grade 0.2: The ratio error is ≤±0.2%, and the phase error is ≤±10 minutes. This grade is widely used in industrial metering to ensure the accuracy of trade settlements.

Grade 0.5: The ratio error is ≤±0.5%, and the phase error is ≤±20 minutes. This grade is suitable for general commercial or residential metering and offers a lower cost. 0.2S and 0.5S: These grades with an "S" maintain high accuracy even under low loads (1% to 120% of rated current). The ratio and angle error ranges are the same as those for grades 0.2 and 0.5, but they have a wider applicable current range (the traditional 0.2 grade only guarantees accuracy within 5% to 120% of the rated current). These grades are suitable for scenarios with large load fluctuations, such as residential electricity consumption.