Cable Engineering Calculators

Cable size, voltage drop, derating, short-circuit withstand, parallel sets, conduit fill and insulation test calculators with stated limits.

A cable has to pass several checks and none replaces the others: it must carry the current after derating, keep voltage drop within the limit, and survive a fault until the protective device clears it. The calculators here cover each check separately so you can see which one decides the size. Work from voltage drop or ampacity, confirm short-circuit withstand, then check physical limits such as parallel sets and conduit fill. The insulation resistance tools support testing once the cable is installed.

Where to start

1. Cable Size for Voltage Drop: Smallest standard conductor that keeps voltage drop within your limit.
2. Cable Derating and Ampacity: Derated current capacity once installation factors are applied.
3. Cable Short-Circuit Withstand: Smallest conductor that survives a fault for the clearing time.
4. Parallel Cable Sets: Number of parallel cables needed for a large design current.

All 17 calculators in this category

Voltage Drop

• Voltage Drop: Voltage drop along a cable from current, length and impedance. Open in Elecmetric
• Maximum Cable Length: Longest run that keeps voltage drop within a limit. Open in Elecmetric
• Voltage Drop from Conductor Size: Voltage drop from conductor material, size (area, AWG or diameter) and temperature, for DC, single-phase or resistive three-phase circuits.
• AC Voltage Drop from Conductor Size: AC voltage drop for single-phase or three-phase circuits from conductor material, size (area, AWG or diameter), temperature, power factor and cable reactance. Open in Elecmetric

Cable and Wire

• Cable Resistance: Conductor resistance from length, cross-section and material. Open in Elecmetric
• AWG to Diameter and Area: Wire diameter and cross-section from an AWG number.
• Cable Derating and Ampacity: Derated current capacity of a cable and the tabulated rating it must start from. Open in Elecmetric
• Cable Size for Voltage Drop: Smallest standard conductor that keeps voltage drop within the limit. Open in Elecmetric
• Cable Short-Circuit Withstand: Smallest conductor that survives a fault for a given clearing time. Open in Elecmetric
• Cable Power Loss (I²R): Heat dissipated in a cable run and the share of the load power it wastes. Open in Elecmetric
• Conductor Resistance vs Temperature: Resistance of a copper or aluminium conductor at its operating temperature. Open in Elecmetric
• Copper vs Aluminium Conductor: Resistance of a copper and an aluminium conductor, and the aluminium size that matches copper. Open in Elecmetric
• Parallel Cable Sets: Number of parallel cables needed for a design current after grouping derating. Open in Elecmetric
• SWG to Diameter and Area: Wire diameter and cross-section from a Standard Wire Gauge (SWG) number. Open in Elecmetric

Conduit and Raceway

• Conduit Fill: Fill percentage of a conduit for a number of equal cables, with the commonly used fill limit. Open in Elecmetric

Testing and Measurement

• Insulation Resistance Temperature Correction: Insulation resistance corrected to a 40 °C reference using the halving-per-10 °C rule of thumb. Open in Elecmetric
• Polarisation Index and Dielectric Absorption Ratio: PI and DAR from timed insulation resistance readings. Open in Elecmetric

What these calculators do not cover

Cross-check: all 17 calculators listed here are compared with 369 reference calculations written separately from the engine. This confirms the arithmetic and selection rules. It does not confirm that a standard table or convention matches your standard or manufacturer data.

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