🔌 Electrical

IS Cable Sizing Calculator

Size electrical cables per Indian Standards (IS 732, IS 1554). Calculate conductor cross-section for current, voltage drop, and short-circuit requirements.

📐 Standard: IS 732 / IS 1554
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IS Cable Sizing Calculator Calculator
Reference: IS 732 / IS 1554
🔌 Electrical
Size electrical cables per Indian Standards (IS 732, IS 1554). Calculate conductor cross-section for current, voltage drop, and short-circuit requirements.
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ℹ️ About This Calculator

The IS cable sizing calculator applies Indian Standard IS 732 (Code of Practice for Electrical Wiring Installations) and IS 1554 (PVC-insulated cables) to determine the correct conductor cross-section. The calculation follows IS 732 derating tables, current capacity tables, and voltage drop limits specifically calibrated for Indian installation conditions (ambient temperatures, soil conditions).

IS 732 and IS 1554 are the fundamental Indian Standards for cable sizing and selection in LV installations. Key difference from IEC 60364/BS 7671: IS 732 uses slightly different base ambient temperature assumptions suited to Indian climate (30°C base vs 30°C in BS 7671; but Indian installations often reach 40–50°C ambient in cable runs). CPWD specifications require IS 732 compliance for all government building electrical work. IS 1554 covers PVC-insulated cables; IS 7098 covers XLPE cables.

📐 IS 732 Cable Sizing Procedure

IS 732 / IS 1554

Design Current:
  I_b = P / (√3 × V × cosφ) [three-phase]
  I_b = P / (V × cosφ)      [single-phase]

Tabulated Current:
  I_t ≥ I_b / (Ca × Cg × Cc)
  Ca = temperature derating (IS 732 Table C1)
  Cg = grouping factor (IS 732 Table C2)
  Cc = conduit/trunking factor

IS 732 Ambient Temperature Derating:
  30°C: Ca=1.08 (PVC); 40°C: Ca=0.91; 45°C: Ca=0.82; 50°C: Ca=0.71

Voltage Drop:
  mV/A/m values from IS 1554 cable data → ΔV% ≤ 5% total

🧮 Worked Example

Example: A three-phase 415V load of 25 kW at 0.85 power factor gives design current I_b = 25000/(√3 × 415 × 0.85) ≈ 41 A. The cable runs in a roof cable tray reaching 45°C ambient (Ca = 0.82) grouped with 3 other circuits (Cg = 0.70), with no conduit factor applied.

Required tabulated current: I_t ≥ 41/(0.82 × 0.70) ≈ 71.4 A, which an IS 1554 16 mm² copper cable can satisfy. Checking voltage drop over a 35 m run at the cable's rated mV/A/m of 2.8: ΔV = 41 × 35 × 2.8/1000 ≈ 4.0 V, or 1.7% - comfortably within the 3% IS 732 limit for final circuits.

❓ Frequently Asked Questions

What ambient temperature should I use for cable derating in India? +
IS 732 base temperature: 30°C (cables in air). In practice: roof cable trays in Indian summers reach 50–55°C (severe derating required); cables in wall conduits in non-air-conditioned areas: 40–45°C; cables in air-conditioned spaces: 30°C. Use 40°C as a conservative default for most Indian buildings unless the installation is specifically in a cooled environment. Never use the IS 732 table values at face value without checking the actual ambient.
What is the difference between IS 1554 and IS 7098 cables? +
IS 1554: PVC-insulated cables (type designation PVC/PVC). Max conductor temperature 70°C. IS 7098: XLPE-insulated cables. Max conductor temperature 90°C (continuous), 250°C (short circuit). XLPE cables carry about 25–30% more current than equivalent IS 1554 cables. For any cable run over 30 m or any cable in a hot environment: IS 7098 XLPE cables provide significant savings in conductor size while meeting the same current requirement.
Does the Indian standard require 3 or 4 core cables for three-phase circuits? +
IS 732: a 3-phase circuit in a balanced system can use a 3-core cable (phases only) if the neutral is not required or the neutral is shared (TN-C earthing not common in India). In practice: all sub-circuit wiring uses 4-core cable (3 phases + neutral) for TN-S systems. 3.5-core cable (full phases + half-size neutral) is used when neutral current is expected to be less than phase current. Earth is provided separately per IS 3043.
What is the maximum permitted voltage drop per IS 732? +
IS 732 limits: 3% for final circuits (from distribution board to socket/load); 5% total from utility meter to the final point of use. For motor circuits: additional allowance – motor can withstand up to 10% voltage variation at terminals, but protection and efficiency suffer above 5%. For IT equipment (computers, servers): keep voltage drop below 2.5% to protect sensitive electronics from voltage sags.
How do I apply the grouping derating factor for cables in a trunking? +
IS 732 Table C2: grouping factor for cables touching each other. 2 circuits: 0.80; 3 circuits: 0.70; 4 circuits: 0.65; 5–6: 0.57; 7–9: 0.50; 10–12: 0.45; 16–20: 0.38. Cables in separate conduits (not touching): no grouping derating. Cables on cable trays with spacing ≥ 1 cable diameter: reduced derating. The IS 732 grouping factors are more conservative than IEC 60364 – always use IS 732 values for Indian projects.

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