Free Earthing Tool

Earthing Conductor Size Calculator

Q: What is the k factor for GI / copper earthing strip?

For a bare conductor from a 30°C initial temperature (IEC 60364-5-54), k for GI / steel is about 50 (150°C final), 58 (200°C), 69 (300°C) and 82 (500°C); for copper it is about 138, 159, 190 and 228 at the same final temperatures. A higher permitted final temperature gives a higher k and so a smaller required cross-section.

Q: Does this calculator include a corrosion allowance?

No. It gives the thermal minimum cross-section by the adiabatic method only. The final selection must also meet the IS 3043 minimum conductor sizes and the corrosion allowance for buried conductors, plus your project specification. Confirm the size with your design engineer.

Size an earthing conductor from the prospective fault current and duration using the adiabatic method (IS 3043 / IEC 60364-5-54), and get the smallest standard GI or copper earthing strip that meets the thermal minimum.

Thermal minimum S (IEC)	—
Recommended strip — IS 3043-safe	—

IS 3043 governs — sized conservatively. This calculator computes the thermal minimum to IEC 60364-5-54, then recommends one standard size up because IS 3043 can require a larger conductor (its minimum conductor sizes, higher ambient basis and the corrosion allowance for buried conductors). Where the tool and IS 3043 disagree, IS 3043 wins. Treat the output as indicative and confirm with your design engineer.

Thermal minimum only. This is the adiabatic cross-section for fault heating. The final selection must also satisfy the IS 3043 minimum conductor sizes and the corrosion allowance for buried conductors, plus your project spec. Confirm with your design engineer.

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Please read. These figures are general projections, not a design. They are estimates based on published formulae, standard weight data and assumed uniform soil conditions — real sites vary, and the numbers here may not be 100% accurate. They are offered as a working aid only. Global Electric Company accepts no liability for decisions taken on the basis of these results: always have them checked and signed off by your site engineer, electrical consultant or a qualified professional, and confirm earth resistance by measurement on site before commissioning. Where these tools and IS 3043 disagree, IS 3043 wins.

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How earthing conductor size is calculated

The minimum cross-section to withstand fault heating is the adiabatic equation from IS 3043 / IEC 60364-5-54:

S = ( I × √t ) ÷ k

where S = minimum cross-section (mm²), I = fault current (A), t = fault duration (s) and k = a material constant for the permitted temperature rise (bare conductor, 30°C initial, IEC 60364-5-54 values). A higher permitted final temperature gives a higher k and a smaller required section. This gives the thermal minimum. Because IS 3043 governs Indian installations and can require a larger conductor, the tool then recommends one standard size above that minimum — conservative rather than optimistic. Where the tool and IS 3043 disagree, IS 3043 wins.

k-factor table (IEC 60364-5-54, bare conductor, 30°C initial)

Material	150°C	200°C	300°C	500°C
Copper	138	159	190	228
GI / Steel	50	58	69	82

Earthing strip cross-sections (mm²)

Strip size (mm)	Cross-section (mm²)
GI / Copper 25 × 3	75
GI / Copper 25 × 6	150
GI 32 × 6	192
GI / Copper 40 × 6	240
GI / Copper 50 × 6	300
GI 75 × 6	450
GI 50 × 10	500
GI 60 × 10	600
GI 75 × 10	750

Copper strips listed up to 50×6 (300 mm²); larger copper sections on request. GI strips beyond 75×10 on request.

Frequently asked questions

How do I size an earthing conductor for fault current?

Use the adiabatic method (the formula is common to both IS 3043 and IEC 60364-5-54): S = (I × √t) / k, with S in mm², I in amperes, t in seconds and k a material constant. Using the IEC 60364-5-54 k value, 25 kA for 1 s in bare GI (k = 58) gives a thermal minimum of about 431 mm² — the smallest IEC strip that meets it is 75×6 (450 mm²). Because IS 3043 governs and can require a larger conductor, size up one standard step to 50×10 (500 mm²). Where the tool and IS 3043 disagree, IS 3043 wins.

What is the k factor for GI / copper earthing strip?

For a bare conductor from 30°C (IEC 60364-5-54): GI / steel k ≈ 50 / 58 / 69 / 82 at 150 / 200 / 300 / 500°C final; copper k ≈ 138 / 159 / 190 / 228 at the same temperatures.

What size GI strip do I need for 25 kA?

At 25 kA for 1 s in bare GI (IEC k = 58, 200°C) the adiabatic thermal minimum is about 431 mm²; the smallest IEC strip that meets it is 75×6 (450 mm²). Because IS 3043 governs and can require a larger conductor, the calculator recommends one standard size up — 50×10 (500 mm²). It changes with fault duration and permitted final temperature.

Does this calculator include a corrosion allowance?

No — it gives the thermal minimum only. The final size must also meet the IS 3043 minimum conductor sizes and the corrosion allowance for buried conductors, plus your project spec. Confirm with your design engineer.