CT Burden & Lead Sizing
Check whether the connected device burden plus secondary-lead burden stays within a CT rated burden and estimate the available lead-length margin.
Calculation method
The lead loop resistance is calculated as R = 2ρL/A using the one-way lead length. Lead burden is Isec²R. The device burden and lead burden are added and compared with the CT rated burden. The maximum one-way lead length is calculated from the remaining VA allowance.
How to use the result
Use the result to compare 1 A and 5 A CT secondary systems, conductor sizes and routing distances. Because lead burden rises with the square of secondary current, a 1 A secondary can provide a large benefit for long secondary circuits.
Engineering limits
Rated burden is only one CT selection parameter. Accuracy class, instrument security factor, protection accuracy-limit factor, excitation curve, knee-point voltage, remanence, transient performance and saturation under fault current are not established by this calculation.
Before design release
Record the source and revision of every project input used in this calculation, then compare the result with the next practical equipment or conductor size rather than treating the numerical minimum as an automatic selection. Check tolerances, environmental derating, duty cycle, protection settings, installation constraints and manufacturer limits that are outside the simplified model. Where the result feeds another study, carry the same voltage, current, power-factor, fault-level and timing assumptions forward so the design chain remains traceable. Save the governing case and the reason for the final engineering choice. ElectroDesigner is intended to make the calculation path visible; it does not replace the project engineer’s verification, the adopted standard or tested manufacturer data.