When configuring the energy meters, the CT and PT ratio calculator must be accurately calculated and set. A small mistake in these settings can lead to major billing or monitoring errors. To save time and ensure accuracy, we’ve built a free CT/PT Ratio Calculator that helps electrical engineers, technicians, and automation professionals quickly determine the correct ratio values.
Table of Contents
What is the CT and PT Ratio?
➤ CT Ratio:
The ratio between the primary current (actual load) and the secondary current (fed to the meter or protection device).
CT Ratio = Primary Current / Secondary Current
Example:
A CT with 600/5 rating → CT Ratio = 600 ÷ 5 = 120
➤ PT Ratio:
The ratio between the primary voltage (line voltage) and the secondary voltage (fed to the meter).
PT Ratio = Primary Voltage / Secondary Voltage
Example:
A PT with 11kV/110V → PT Ratio = 11000 ÷ 110 = 100
Use the Free CT and PT Ratio Calculator
Why Use a CT/PT Calculator?
- Eliminates manual calculation errors
- Saves time during site commissioning
- Useful for meter setup, energy audits, and system design
- Beginner-friendly for students and junior engineers
Important Tips for CT/PT Configuration
| Aspect | Recommendation |
| CT Polarity | Always match ‘P1’ to source side |
| Accuracy Class | Use 0.5 or better for metering |
| Secondary Load | Do not leave CT secondary open |
| PT Fusing | Always fuse PT secondary to avoid faults |
Tools You May Need
- Clamp Meter with CT Range
- Digital Multimeter – True RMS
- Protective Fuse Box for PT Secondary
Final Thoughts
A reliable CT/PT ratio calculator simplifies a critical task in electrical system design and maintenance. Bookmark this page and use it every time you’re configuring a new MFM meter or protection relay.
