Electricity Usage and Measurement
Current Transformer Reading Calculator
The purpose of Current Transformer Reading is to turn meter secondary reading and CT ratio into primary current. Keep the source condition with the saved result so later comparisons remain meaningful.
Enter values for Primary current
Enter ratings or measurements that describe one scenario.
How the result is calculated
This page evaluates primary = secondary × CT ratio. Only Meter secondary reading and CT ratio enter the numerical result.
For the example shown, primary current equals 640.00 A. Treat that value as a demonstration, not a recommendation.
Calculate primary current from meter secondary reading and CT ratio. Energy represented can be checked separately in Electricity Meter Pulse Calculator.
Interpreting the answer
The calculated Primary current is meaningful only with its input conditions attached. Compare it with base, peak, and changed-operation scenarios.
A result without its source conditions is difficult to compare or audit.
Values this page needs
Separate real power, apparent power, energy, and demand before entering values. Do not combine a worst-case value with unrelated nominal data.
Check every prefix before entry; micro, milli, kilo, and mega are not interchangeable.
- Meter secondary reading
- Default example: 3.2 A. Enter meter secondary reading in A.
- CT ratio
- Default example: 200. Enter CT ratio.
What the formula leaves out
Include any programmed meter ratio.
Outside the entered variables, consider fixed charges, demand ratchets, seasonal rates, uncertainty, and future load change. Document which effects were checked elsewhere in the analysis.
Separate real power, apparent power, energy, and demand before entering values.
Keep a reproducible record
Save meter secondary reading and CT ratio with primary current. Add the date and any unit conversion.
Carry primary current as the raw numerical value until the final step. Do not round between dependent calculations.
Using this result in a larger analysis
Review meter secondary reading and the remaining entries as one case. If one value belongs to another temperature, load, or time period, separate the scenarios.
Use primary current alongside billing rules, meter data, demand intervals, and operating schedules. Preserve the unrounded number until all dependent calculations and comparisons are complete.
Document any effect handled outside this page, especially meter accuracy, sampling interval, waveform bandwidth, and conversion loss. That note prevents a later reader from assuming the simple equation covered it.
Common questions before using the result
Which assumptions matter most here?
Include any programmed meter ratio. Also consider meter accuracy, sampling interval, waveform bandwidth, and conversion loss.
Why does the field result disagree with this page?
Recheck units and operating state before investigating meter accuracy, sampling interval, waveform bandwidth, and conversion loss.
What should remain fixed in an alternate case?
Use separate labeled cases when more than one condition changes. Record meter scaling, time period, load profile, and applicable tariff.
What else is required before final selection?
Use the number as one check, then review the relevant tariff and measured load profile.