CT Ratio Calculator for Current Transformers
Calculate the correct current transformer ratio for protection and measurement systems.
Use this CT ratio calculator to determine recommended current transformer ratio based on primary current rating, safety margin, and secondary current output.
Circuit Parameters
Load Information
A
CT Output Specification
Recommended CT
Standard Size
Ideal CT Ratio
400:5
Based on calculated 350A requirement
Primary Rating
400
A
Standard manufactured primary
Meter Configuration
Multiplier
CT Multiplier (CTR)
80
x
Use this factor for your energy meter
Engineering Reference
Target Primary Formula
Target = Max Load × Margin
Multiplier Formula
CTR = Primary / Secondary
- Target = Minimum required CT Primary
- Margin = 1.0 to 1.5 (Usually 1.25)
- CTR = Current Transformer Ratio
- Info = Auto-snaps to standard sizes (50, 100, 200... up to 6000A)