Cable Volt Drop Table

Overview

The Cable Volt Drop Table generates a 34×17 reference matrix showing the maximum cable length (metres) for every motor size × cable size combination, based on running voltage drop per AS/NZS 3008.1.1:2017. The cable voltage drop factors V_c are read from the licensed Table 42 data (copper multicore cables, circular conductors) at the rated conductor temperature of the insulation you select.

Unlike single-point cable sizing calculators, this tool produces a complete "waterfall" matrix — allowing you to quickly look up the maximum cable run for any motor and cable combination at a glance.

Matrix cells are colour-coded:

• Green — up to 100m
• Yellow — 100m to 500m
• Red — over 500m
• Grey (N/A) — cable current capacity is less than motor FLC
• Grey (> Max) — calculated length exceeds the max display cap

Input Parameters

Output Results

The main output is a 34-row × 17-column matrix where:

• Rows — 34 motor sizes from 0.37kW to 750kW (FLC tabulated at 415V, scaled to the system voltage)
• Columns — 17 cable sizes from 2.5mm² to 500mm²
• Cells — maximum cable length in metres (rounded integer), or N/A / > Max

Summary statistics are also provided:

• Total combinations (34 × 17 = 578)
• Valid combinations (cells with a numeric length within display range)
• N/A count (cable too small for motor)
• Exceeds max count (length beyond display cap)

Formulas

Maximum Cable Length

L = (Vd% × V × 1000 × P) / (I × Vc)

Where:

• L = Maximum cable length (m)
• Vd% = Voltage drop as a decimal (e.g. 0.05 for 5%)
• V = System voltage (V)
• P = Number of parallel cables
• I = Full load current at the system voltage (A): \(I = I_{415} \times 415 / V\) (same kW, efficiency and power factor, so current is inversely proportional to voltage)
• Vc = Cable three-phase voltage drop factor (mV/A.m): AS/NZS 3008.1.1:2017 Table 42, copper multicore circular, maximum-value column (\(V_c = \sqrt{3}\,Z_c\), valid for any load power factor), at the rated conductor temperature of the selected insulation

Effective Current-Carrying Capacity

CCC_eff = CCC_base × P × k_derating

Where k_derating = 0.9 when P > 1, otherwise 1.0. If CCC_eff < FLC, the cell is marked N/A.

Cable Data (Cu Multicore, 3-Phase)

Voltage drop factor V_c

V_c comes from the licensed AS/NZS 3008.1.1:2017 data installed on the server; the values are not reproduced here. Every cable size is read from Table 42 (three-phase, copper, multicore cables with circular conductors, maximum value) in the column for the insulation's rated conductor temperature, because a cable carrying a motor's full-load current is assumed to run fully loaded:

The calculation report names the table and column used. A hotter column gives a larger V_c and a shorter maximum length: for the same cable, the 90 °C column is about 5 % above the 75 °C one (less for the largest sizes, where reactance is a larger part of the impedance). A combination the installed edition does not tabulate is reported as an error naming the input to change; no substitute value is used.

Current screen

The N/A screen uses the component's indicative derated ratings below (one fixed installation condition; the source data took PVC values for 2.5–16 mm² and XLPE values for 25–500 mm²). They do not change with the insulation input and are not a substitute for a current-carrying capacity check.

Motor Data (FLC at 415V)

* The source data had these two currents transposed (450 kW = 892 A, 500 kW = 830 A, a larger motor drawing less current). Corrected 2026-10-23 to 450 kW = 830 A (1.84 A/kW) and 500 kW = 892 A (1.78 A/kW), in line with 400 kW (1.83 A/kW) and 550 kW (1.81 A/kW).

Worked Examples

The 11 examples below are the validation cases for this calculation. Each one was produced by the calculation engine from the inputs shown, every figure was checked against the independent reference quoted at the end of the example, and the same cases are run against every engine build (see validation scorecard, tool fe_calc_voltage_drop; worked examples for every calculation).

Standards & References

• AS/NZS 3008.1.1:2017 — Electrical installations – Selection of cables. Table 1 for the insulation's maximum conductor operating temperature, Table 42 for the three-phase voltage drop factors (copper multicore, circular conductors); Table 13 is the basis the source data names for the indicative ratings.
• AS/NZS 3000:2018 — Electrical installations (Wiring Rules). Clause 3.6 covers voltage drop requirements.

Tips & Limitations

• The 0.9 derating factor for parallel cables is a simplified approach per AS3008 for grouped cables. Actual derating may vary by installation method.
• Motor FLC values are tabulated for 415V, 3-phase and scaled by 415 / V for other system voltages (the same motor output draws a current inversely proportional to voltage). The voltage in the numerator of the length formula is a separate effect: both apply.
• This calculator computes running voltage drop only (not startup). Startup voltage drop (typically allowed up to 15-20%) is handled separately.
• V_c is taken at the insulation's rated temperature (fully loaded cable). A cable loaded well below its rating runs cooler and reaches further; the matrix is conservative for it.
• Copper multicore cables only. Aluminium and single-core cables have their own Table 40–45 values; use the Cable Voltage Drop calculator for them.
• The matrix is too wide for A4 PDF — it is available only in the interactive web view. The PDF report includes the formula, cable data reference, and statistics.

Developer Guide — Architecture

This calculator follows the standard calcs component pattern:

components/c0035_cable_volt_drop_table/
├── __init__.py              # Docstring
├── apps.py                  # Django AppConfig
├── calculations.py          # Pure Python — all math, no Django
├── component.py             # Schema, Calculator class, builders, registration
├── equations.py             # LaTeX equation templates
└── templates/.../sidebar_form.html  # Vue 3 sidebar form

Data flow: Sidebar form → CableVoltDropTableCalculator.calculate() → calculate_cable_volt_drop_table() (pure Python) → results dict → equation_builder() / summary_cards_builder() → UI rendering

Developer Guide — Code Paths

Developer Guide — Testing

# Run all tests for this component
pytest calcs/test_c0035_cable_volt_drop_table.py -v

Test coverage includes:

• TestLookupVcFactors — Table 42 column per insulation (75/90/110 °C), edition and gap errors; rows are served from transcribed values (the licensed data is not in the test database), and a dev-database test checks them against the installed tables
• TestCalculateMaxCableLength — known formula values, parallel doubles length, higher Vd% increases length
• TestGetEffectiveCCC — single no derating, 2 cables with 0.9 derating, 4 cables
• TestClassifyCell — green/yellow/red boundaries, exceeds_max, N/A
• TestBuildVoltDropMatrix — 34 rows × 17 cols, N/A for undersized cable, stats
• TestCalculateCableVoltDropTable — defaults, spot-check cell, input echo
• TestCalculatorClass — validation, round-trip calculation, registration