Sizing Guide
GI Earthing Strip Sizes: What IS 3043 Actually Requires
When specifying GI strip sizes for earthing, the default approach for many is to simply copy the last project's Bill of Quantities. But getting your IS 3043 GI patti specifications correct means understanding the actual thermal minimums your system must handle during a fault.
This sizing guide covers how strip sizing actually works, the full range of standard sizes stocked, and the mistakes that leave a BOQ short.
The Method
How IS 3043 sizing actually works
Sizing an earthing conductor isn't guesswork; it is determined by the prospective fault current and the duration of that fault. Engineers use the adiabatic method: it assumes that during a short circuit, the temperature rise happens so fast that no heat escapes the conductor. The metal must have enough cross-sectional area to absorb all that fault energy without degrading before the breaker trips.
The formula is S = I√t / k, where the required cross-section (S) depends on the fault current (I), the duration (t), and a material constant (k).
While international standards like IEC 60364-5-54 provide specific k-factors for adiabatic sizing, IS 3043 uses different constants — and because of that difference, IS 3043 can require a larger conductor than the IEC maths suggests.
To run these projections, use our Conductor Size Calculator. It computes the IEC 60364-5-54 minimum cross-section and recommends a standard GI or copper strip. These are projections, not a final design; where the tools and IS 3043 disagree, IS 3043 wins.
The Size Chart
The size chart: every size we stock
The base steel for our flats is manufactured to IS 2062, hot-dip galvanised for corrosion resistance underground. All eight standard sizes are stocked in Bengaluru:
| Size (mm) | Cross-section | Typical use |
|---|---|---|
| 25 × 3 | 75 mm² | Light residential, sub-mains earthing |
| 25 × 6 | 150 mm² | Apartments, villas, commercial buildings — the standard default |
| 32 × 6 | 192 mm² | Mid-size commercial, hospitals |
| 40 × 6 | 240 mm² | Large commercial, industrial earthing |
| 50 × 6 | 300 mm² | HT substations, large industrial plants |
| 50 × 10 | 500 mm² | Heavy industrial, transformer earthing |
| 60 × 10 | 600 mm² | Power plants, heavy industry |
| 75 × 12 | 900 mm² | EHV substations, grid-scale infrastructure |
When you weigh a sizing decision — say 25×6 vs 50×6 — you are comparing the cross-sectional area available to absorb the fault. A 50×6 strip carries twice the section of a 25×6, so twice the thermal capacity. The 25×6 remains the standard default for most residential and mid-rise commercial buildings; larger sections belong to higher fault levels, not to "better safe than sorry" padding — oversizing wastes money the BOQ never gets back. See the full product page for specifications and MTC details.
Weight & Galvanising
Calculating weight — and the galvanising reality
A common procurement issue is converting the specified strip into tonnage. Custom sizes can be computed from theoretical density — 7.85 g/cm³ for bare steel. But hot-dip galvanising adds a layer of zinc, so trade chart values for GI sit about 2% above bare-steel theory. Our standard sizes use the Global Electric Company weight chart, which accounts for the zinc — it is the trade quoting basis and the exact figures we invoice against.
Convert metres to kilograms (or back) with the Strip Weight Calculator before you ask for a rate.
Watch For
Common mistakes in specification
- Relying on theoretical mass. Trade weights run above bare-steel theory. Using 7.85 g/cm³ for galvanised material leaves your BOQ short on tonnage.
- Assuming IEC constants map to Indian Standards. IS 3043 can require a larger conductor. Always have the sizing checked and signed off by a site engineer or electrical consultant.
- Copying the last project's BOQ. Fault levels differ between sites; the size that passed the last inspection is not automatically correct for this one.
When To Ask Us
When to ask us
Once your design is signed off, getting a rate is simple — we quote today's actual rate, not a stale list price. Include all three and you'll usually get the number in one reply:
- Size — e.g. 50×6 mm GI strip (GI patti)
- Quantity — in kg, or in metres and we'll convert
- Delivery location — the Bengaluru site or godown
WhatsApp us your size, quantity and delivery location — today's rate back, usually within the hour. Material Test Certificate with every order.
Related Guides
Related guides
- What Goes in an Earth Pit — the five components of an IS 3043 earth pit.
- Copper vs GI Earthing — when GI is enough, and when copper earns its premium.
- How to Read an MTC — what a test certificate proves — and what it can’t.
Get Today's Rate on Your Size
Send your size, quantity and delivery location. We quote against today's steel market, with a Material Test Certificate on every order.