Cable & conductor sizing

Cable Sizing Calculator

Size a cable by ampacity, voltage drop and short-circuit withstand — to IEC 60364-5-52 or NEC Table 310.16.

IEC 60364 NEC 310.16

For low-voltage installations up to 1000 V AC. Not for medium- or high-voltage cable (which uses IEC 60287).

Inputs

System

Design current (Ib)

Full-load / design current of the circuit.

System voltage

Line-to-line for 3-phase; supply voltage for 1-phase.

Conductor material

Insulation

Installation method

IEC 60364-5-52 reference installation method.

Conductor temperature rating

Terminations often limit this to 60 or 75 °C (NEC 110.14(C)).

Run length (one way)

Cable route length in one direction.

Voltage-drop limit

Typical: 3% final circuits, 5% total.

Ambient temperature

°C

Grouping

Number of grouped circuits (1 = a single circuit).

Short-circuit withstand (optional)

Prospective fault current

Leave blank to skip this check.

Protection clearing time

Disconnection time of the protective device.

Results update automatically as you enter values.

Result

Enter your circuit details — the recommended conductor size appears here.

How this size is chosen

A conductor must pass three checks, and the size is set by whichever is strictest:

1. Ampacity — the cable's current-carrying capacity, after derating for ambient temperature and grouping, must be at least the design current. 2. Voltage drop — the drop over the run must stay under your limit (often 3–5%). Long runs are usually decided here, not by ampacity. 3. Short-circuit withstand — during a fault, the conductor must not overheat before the protection clears (adiabatic check, IEC 60364-5-54).

The course walks through why each check exists and how to defend the final size in a design review.