Current transformer ratio defines the relationship between the primary and secondary currents, typically expressed as ratios such as 300:5 or 600:1, enabling accurate current scaling for metering, protection relays, and safe measurement in electrical power systems. Comprehensive reference chart for current transformer (CT) ratios from 50A to 6000A. For example, a 400:5 CT steps down 400 Amps to 5 Amps—an. Many CTs offer multiple tap ratios for flexibility: To select CT ratios for accurately measuring load current: To select CT ratios for protection relays considering short circuit requirements: 🏭 Factory Experience: Based on our manufacturing and application experience: 70% of CT primary rating. We can define the CT ratio as the ratio of primary current to secondary current. In the mathematical expression, we can write it as; What does it mean if the CTR (CT Ratio) of the CT is 1000/5? It means when the primary of the CT carries 1000 amperes current, then the secondary of the CT will carry. Accurate current transformer (CT) sizing keeps protection relays, meters, and advanced analytics operating within specification. Engineers searching this keyword expect practical guidance: formulas, standards references, and integration advice for medium- and low-voltage systems. Current transformers for protection relays, as opposed to those use strictly for metering purposes, have an IEEE standard classification.
