Cable & Wire Sizing Calculator

Supply Type

Current Type

AC 1-Phase

AC 3-Phase

System Voltage (V)

Load Parameters

Input Method

Current (A)

Power (kW)

Design Current (A)

Power Factor

Load Type / Notes

Cable Parameters

Cable Length One Way (m)

Conductor Material

Copper

Aluminium

Insulation Type

Max Permissible Voltage Drop (%)

Installation & Derating

Installation Method (IS 3961)

Ambient Temperature (°C)

Number of Cables / Circuits Grouped

Additional Safety Margin (%)

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Recommended Cross-Section

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IS 3961 / IS 694

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Design Current (A)

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Derated Capacity (A)

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Voltage Drop (%)

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Derating Factor

Calculation Details & Breakdown

Method	Description	Relative Factor	Best For
A1	Conduit in thermally insulating wall	0.77	Building wiring (insulated wall)
A2	Multi-core cable in conduit in wall	0.82	Building wiring (cavity wall)
B1	Single cable in conduit on wall	1.00 (reference)	Industrial / standard
B2	Multi-core cable in conduit on wall	0.94	Industrial / standard
C	Clipped direct to wall / cable tray	1.00	Industrial plants
D	Direct buried / underground duct	0.97	HT / LT underground
E	In free air — horizontal tray	1.18	Overhead bus-duct, open racks
F	In free air — vertical tray	1.18	Riser shafts, vertical drops

Applicable Indian Standards

IS 3961 — Current Ratings for Cables (Parts 1–5)
IS 694 — PVC Insulated Cables (up to 1100 V)
IS 1554 — PVC Sheathed Heavy Duty Cables
IS 7098 — XLPE Insulated Cables (Parts 1–3)
NBC 2016 Part 8 — Electrical Installations
IE Rules 1956 (Amended 2010)
IS 11171 — Short Circuit Rating of Cables
IEC 60364 (reference)

Voltage Drop Limits (Typical)

LT supply up to 1 kV — 5% max (IE Rules)
Motor circuits — 3% at full load
Motor starting — up to 15% permissible (momentary)
Lighting circuits — 3% max (NBC 2016)
Sensitive / electronic loads — 2–3%
Sub-mains from panel — 1.5% typical
DC systems (24 V / 48 V) — 2–3%
Long rural feeders — consult utility / DISCOMs

Selection Criteria (Priority Order)

1. Current carrying capacity (Iz ≥ Ib / derating)
2. Voltage drop within permissible limit
3. Short circuit rating (check fault level)
4. Mechanical protection requirements
5. Starting current / inrush (for motors)
6. Future load growth (add 20–25% buffer)
7. Economics — cost vs. life-cycle losses
Always select the larger size if criteria conflict

Material Properties (IS)

Copper resistivity: 0.0172 Ω·mm²/m @ 20°C
Aluminium resistivity: 0.0280 Ω·mm²/m @ 20°C
Copper temp correction to 70°C: ×1.26
Copper temp correction to 90°C: ×1.38
Aluminium temp correction to 70°C: ×1.26
DC: multiply resistance by 2 (both conductors)
AC 1-Phase: multiply resistance by 2
AC 3-Phase: multiply resistance by √3 ≈ 1.732

Key Formulas Used

Design Current

Ib (AC 1Ph) = P / (V × PF)

Ib (AC 3Ph) = P / (√3 × V × PF)

Ib (DC) = P / V

Derating

Total Derating = Ct (temp) × Cg (grouping)

Required Iz = Ib / Total Derating

Cable Resistance

R/m = ρ₂₀ × Ktemp / A [Ω/m, where A is mm²]

Voltage Drop

VD (1Ph / DC) = 2 × Ib × R/m × L (V)

VD (3Ph) = √3 × Ib × R/m × L (V)

VD% = VD / V × 100

Disclaimer: This calculator is for preliminary sizing purposes. All cable selections must be verified by a qualified electrical engineer against actual IS 3961 tables, fault level calculations (IS 11171), and site-specific conditions before implementation. Results are indicative and based on tabulated IS 3961 data for standard PVC/XLPE copper and aluminium cables.