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AU conduit capacity calculator & type selector

AS/NZS 3000-compliant conduit fill calculation for Australian installations. Pick conduit type (rigid PVC heavy / medium, corrugated LDPE orange, steel rigid / flex) and size (16–150 mm OD), add cable rows with OD + quantity — get fill % vs the 1-cable (53%) / 2-cable (31%) / 3+ cable (40%) limits with bend de-rating. Reverse-calc: given a cable mix, find the smallest compliant conduit per type. Plus a cable OD reference (Cat 5e/6/6A, TPS, single-core V75/V90, fibre, HDBaseT) and an AS/NZS 2053 type selector for in-slab / direct-buried / exposed / hazardous environments.

This tool is provided as-is, for educational and planning purposes only. Conduit sizing decisions must be verified by a licensed electrician against the current AS/NZS 3000 Wiring Rules, AS/NZS 3008.1.1, AS/NZS 2053, and the cable manufacturer's spec sheet for actual outer diameters (specs vary 0.5–1 mm between brands). The Tech Space makes no warranty and accepts no liability. Full disclaimer →

1. Fill Calculator

Add the cables that need to go through the conduit. Pick the conduit type + nominal OD. Tool computes total cross-section, fill %, and verdict against the AS/NZS 3000 fill rule (1 cable = 53%, 2 cables = 31%, 3+ cables = 40%) with per-bend de-rating.

Cables in this conduit

How the de-rate works AS/NZS 3000 doesn't formally mandate per-bend reduction, but the standard reference is the cable manufacturer's pull-tension limits (typically 60–110 kg for UTP). Each 90° sweep adds roughly 50% effective length to the pull. As a planning rule the tool reduces effective fill capacity by 5% per bend beyond the first — so 0 or 1 bend = full limit, 2 bends = 95%, 3 bends = 90%, 4 bends = 85% (cap at 70%). For runs with 4+ bends, plan a draw box.

2. Recommend a size

Given the cable mix from Section 1, the tool finds the smallest standard conduit OD in each type family that meets the AS/NZS 3000 fill limit (with the same bend de-rate).

3. Conduit type selector

Pick all environment factors that apply — tool recommends the right AS/NZS 2053 conduit type with rationale. Multiple criteria narrow the choice (e.g. direct buried + flexibility needed at termination → heavy-duty corrugated for the run + liquid-tight for the termination).

Where is it going?

Mechanical / environment

Special

4. Cable OD reference

Common Australian cables with manufacturer-typical outer diameters. Brands vary ±0.5–1 mm — for production designs, always check the actual cable's data sheet. Click a row to add it to the Fill Calculator above (qty 1).

TypeDescriptionOD (mm)CSA (mm²)

5. AS/NZS rules reference

AS/NZS 3000 fill limits

Number of cablesMaximum fill % of conduit internal areaWhy
1 cable53%Single cable can use most of the conduit area — no jam ratio risk.
2 cables31%"Jam ratio" — when 3 cables of similar size try to wedge as a triangle in a circular bore.
3+ cables40%Cables rearrange into a stable packed configuration; standard limit.

Per-bend de-rate (planning rule of thumb)

Number of 90° bendsEffective fill capNotes
0 – 1100% of AS/NZS limitStraight or single-sweep run — no de-rating.
295%L-bend type runs. Typical residential / commercial.
390%Complex routing. Consider draw box if pull is > 20 m.
485%Add a draw box. Pull tension on UTP becomes a real risk.
5+70%Draw box MANDATORY. Pull from both ends.

Standard nominal sizes (AS/NZS 2053)

Nominal OD (mm)Rigid HD ID (mm)Rigid MD ID (mm)Corrugated effective ID (mm)

References

  • AS/NZS 3000:2018 Wiring Rules — Section 3 cable installation (clause 3.10 covers conduit fill)
  • AS/NZS 2053 — Conduits and fittings for electrical installations (rigid PVC, corrugated, metal types)
  • AS/NZS 3008.1.1:2017 — Selection of cables, including bunching de-rates
  • AS/NZS 4117 — Surge protection (where conduit choice intersects with electrical protection)
  • AS/NZS 2062 — Electrical installations — hazardous areas (gas) — drives metal conduit requirement in Zone 1/2 areas