Current Transformer Ratio Calculator
Calculate CT ratio and estimate primary current from nameplate primary/secondary ratings and measured secondary current.
Enter instrument values
CT conversion
About this calculator
Calculate CT ratio and estimate primary current from nameplate primary/secondary ratings and measured secondary current.
This arithmetic estimate does not assess CT accuracy class, burden, saturation, polarity, waveform distortion, or suitability for protection or billing.
Method and assumptions
CT ratio = rated primary current ÷ rated secondary current. Estimated primary current = measured secondary current × CT ratio.
Calculated results reflect only the ratios, spans, burdens, and readings entered. Verify instruments, wiring, polarity, configuration, and manufacturer limits independently.
FAQs
Can I open or disconnect a current transformer secondary while energized?
No. Never open an energized CT secondary. Follow approved electrical safety procedures and manufacturer instructions.
Does a calculated value verify billing or instrument configuration?
No. Confirm whether the meter or register already applies CT/PT scaling and verify the configured ratios with the metering documentation.
Sources
Use instrument nameplates, meter configuration records, transmitter setup data, and manufacturer compliance-voltage specifications for the installed equipment.