2.08, '12' => 3.31, '10' => 5.26, '8' => 8.37, '6' => 13.3, '4' => 21.2 ]; $cross_section = $awg_data[$wire_size_awg] ?? 3.31; // mm2 // Material resistivity (ohm * mm2 / m) at 20C $rho_20 = ($conductor_material === 'copper') ? 0.0172 : 0.0282; // Temperature correction coefficient (approx 0.00393 for copper, 0.00403 for aluminum) $alpha = ($conductor_material === 'copper') ? 0.00393 : 0.00403; $rho_temp = $rho_20 * (1 + $alpha * ($ambient_temp - 20)); // Total round trip resistance (Ohms) = (2 * length * rho) / (cross_section * parallel_runs) // length in meters (assuming lead_length is round trip or one way? Let's treat lead_length as one-way, round trip = 2 * length) $round_trip_length = 2 * $lead_length; $conductor_resistance = ($round_trip_length * $rho_temp) / ($cross_section * max(1, $parallel_runs)); // CT Max allowed burden impedance (Z_total = VA / I^2) $max_burden_impedance = $burden_va / pow($ct_current, 2); // Actual burden impedance connected (Lead Resistance + Internal Instrument Burden approx if needed, but let's focus on lead resistance vs max allowed) // Voltage drop across leads = I * R_lead * safety_factor $lead_voltage_drop = $ct_current * $conductor_resistance * $safety_factor; // Total burden check $status = ($conductor_resistance <= ($max_burden_impedance * 0.8)) ? 'Acceptable' : 'Warning: High Burden / Voltage Drop'; $result = [ 'resistance' => round($conductor_resistance, 4), 'max_impedance' => round($max_burden_impedance, 4), 'voltage_drop' => round($lead_voltage_drop, 4), 'status' => $status, 'cross_section' => $cross_section ]; } ?> Current Transformer Secondary Wire Sizing Calculator

Current Transformer Secondary Wire Sizing Calculator

Use this advanced calculator for precise electrical wire sizing designs. Determine exact conductor requirements for your secondary metering circuits. Optimize your electrical systems today.

CT & Burden Parameters

Conductor Specifications

Environmental & Advanced

Formula Used

The secondary wire sizing calculation relies on standard electrical engineering principles for current transformer burden evaluation:

How to Use This Calculator

  1. Select your CT secondary current rating ($1\text{ A}$ or $5\text{ A}$).
  2. Input the manufacturer's rated burden in VA and power factor.
  3. Provide the one-way lead distance between the CT and the control panel.
  4. Choose your conductor material, gauge size, parallel runs, and ambient temperature.
  5. Click Calculate Wire Size to review immediate system compliance status.

Complete Guide to Current Transformer Secondary Circuit Sizing

Proper design of current transformer secondary wiring is vital for ensuring accurate metering and reliable protective relay operation in power systems. When fault conditions occur, high currents pass through the primary winding, creating secondary currents that must travel through long control cables without suffering excessive attenuation or distortion.

Why Wire Sizing Matters

If the secondary lead resistance is too high, the total connected burden will exceed the CT class rating. This results in saturation issues, inaccurate metering readings, and potential failure of protection schemes during high-fault scenarios. Utilizing robust copper or aluminum conductors with appropriate cross-sections mitigates these risks effectively.

Frequently Asked Questions

What is the difference between 1A and 5A CT secondary ratings?

A 5A secondary experiences higher power losses over long distances due to $I^2R$ scaling, whereas a 1A secondary tolerates significantly longer wire runs with smaller gauge conductors.

Why is round-trip length used in calculations?

Current must travel out from the CT to the relay and return back to complete the closed electrical loop, doubling the effective conductor length.


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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.