Earthing design

Earthing Design is a preliminary earthing calculation for the layout you have generated. It works out how many earth pits the plant needs and where they go, which GI strip or Cu cable size each earthing connection needs, whether the plant grid meets its resistance target and the touch-voltage limit, and what all of it adds up to as a bill of quantities. It draws the earthing plan over the plant and exports the plan, the calculation and the quantities.

The design basis is IEC. IS 3043 and IEEE 80 figures are worked out alongside as cross-checks and printed next to the IEC ones, so a reviewer working to either can see both.

Opening it

Two routes open the same window:

• Tools ▸ Earthing Design… on the menu bar. Before a layout exists it answers with Generate first — "Generate a layout first, then open Earthing Design."
• ⚡ Earthing Design, the last of the five buttons in the Studies card on the Tools tab. It is greyed out until a layout exists.

The window works on every plot of the layout that holds tables; water plots and plots with no tables are left out.

The window

Earthing Design opens beside the main window rather than in front of it, so you can keep it open while you work; it can be minimised and maximised. A verdict banner runs across the top. The inputs sit on the left in a scrolling column; the results sit on the right in three tabs, Layout, Calculation and BoQ; the exports are in the footer.

There is no Run button. The window calculates as it opens, and again a moment after you stop changing an input — about a third of a second. Every field applies to every design: fixed tilt or tracker, string or central inverter. The system frequency is taken as 50 Hz.

Inputs

Seven groups, in the order they appear.

Soil & site

With the defaults the design resistivity is 150 Ω·m.

Fault data

Targets

Earth pit (maintenance-free)

Conductors

The size lists take commas or semicolons, × for x, in any case. An entry that cannot be read turns the banner to Check the size lists — "GI strip sizes are width x thickness (e.g. 25x6, 50x10); Cu cable sizes are mm² (e.g. 16, 35)." — greys out the three exports with "Fix the inputs to export", and leaves the results at the last calculation that worked.

Equipment rules

Layout rules

What gets earthed

The network is built plot by plot:

• a GI row runner along every table row — east–west near the south edge on fixed tilt, north–south along the centre line on trackers — broken at gaps wider than Row runner gap split, with cross links between rows within Max cross-link length, and an MMS link allowance for every table;
• a Cu cable from each inverter or SMB to the nearest row runner;
• strip along the MV and AC trenches, when that option is on;
• a ring 1.5 m round each ICR, with pit groups at its corners and transformer-neutral pits south of it — the transformer count comes from the electrical grouping, or the fallback;
• USS and MCR rings with their pits, and the auxiliary-transformer pits; weather-station pits beside the MCR;
• a ring of pits round each lightning arrester;
• fence, gate, CCTV and street-light pits — local pits, not bonded to the grid and not drawn with a strip, each counted with its link allowance;
• L-shaped strips tying any isolated part of the network to the rest;
• on trackers only, a bonding jumper at each pile of the pile pattern, or estimated from the bearing spacing when there is none.

Each strip and cable total is the drawn length plus the allowances, plus Wastage. A site with several plots gets one network and one grid check per plot; the banner reports the worst.

Method and standards

Conductor sizes

Each connection is sized for its fault duty from S = I·√t / k, with k for galvanised steel taken from the initial and final temperatures — 68.7 on the defaults. The required area is the larger of that and 90 mm², plus the corrosion allowance, and the strip chosen is the smallest in your list that meets it and is at least 3 mm thick. There are four duties: Main grid (the ICR and MCR rings, transformer bodies and neutrals, the HT panel, the MV backbone), Array field — LV (row runners, cross links, MMS links, AC-trench strip, central inverters), Lightning arrester, and Fence, gates & poles — the last two at the minimum size. Show HV in report adds an HV switchyard duty to the report only. On the defaults that gives 50x10 for the main grid and 25x6 for the rest.

The Cu cable is sized from the LV fault with k = 143 and a 6 mm² minimum, and carries no corrosion allowance — 35 mm² on the defaults. If no listed size is big enough for a duty, the report says so and asks for a larger size.

Earth pits

One pit on the defaults comes to 32.45 Ω by the IEC method (34.87 Ω by IS 3043). The Pit rule decides what happens next:

• One pit per point, bonded to grid (the default): each equipment point gets one pit, bonded to the main grid, so the whole-plant value applies at every point. When one pit alone misses Each earth pit, the report notes it and the banner adds "One pit alone is R Ω; bonded to the grid it takes the plant value."
• Add pits until each point meets target: pits are added in a line at each point until it meets Each earth pit on its own — ten pits on the defaults.

Each arrester gets a ring of at least Min. pits per LA, grown until it meets LA earth pit — five pits on the defaults. The report also gives the electrode length one pit would need to meet its target alone, and warns when the electrode is shorter than 2.5 m, the rod thinner than 15 mm, or the pit spacing less than twice the electrode length.

Plant grid and touch voltage

The IEC grid resistance depends only on the plot's area and the design resistivity: adding strip or pits does not lower it. The IEEE 80 figure does respond to the network, and the resistance carried forward is the larger of the two. When the IS 3043 or IEEE 80 figure misses Whole plant, supplementary pits are added along the array until both meet it. When the plot's area alone puts the target out of reach, no pits are added and the report says so, suggesting a grid extended outside the array (counterpoise) or soil treatment.

For touch and step, the grid current is the MV fault current × Split factor × a decrement factor from X/R and the duration; the earth potential rise is that current × the grid resistance. The IEC check passes when the earth potential rise, or failing that the mesh touch voltage, is within the permissible touch voltage — allowing for footwear and the gravel layer.

Results

The verdict banner

The banner reads "n earth pits · plant grid R Ω (target ≤ T Ω)", with the strip lengths by size and the Cu cable length under it. It is green when every plot meets the Whole plant target and passes the IEC touch check, and amber otherwise, adding "The grid misses its IEC target or touch limit — see Calculation." Per-point and arrester targets do not change it; they are marked in the report.

Layout

The earthing plan over the plant — boundary, tables, ICRs, the MCR and the inverters in the background — with the strips coloured by duty (main grid red, array and AC trench blue, arresters purple, fence and poles grey, Cu cable green dashed), a marker for each kind of pit, and a legend with the count of each. The plot toolbar zooms and pans it.

Calculation

The calculation as a report, each check marked ✓ OK or ! Not met, in numbered sections: 1. Design basis, 2. Key inputs, 3. Conductor sizing (GI strip / Cu cable), 4. Earth pit design, 5. Plant earth grid resistance (Ω) (one row per plot), 6. Touch & step voltage (MV earth fault), 7. Where each earthing connection goes, 8. Earth pit count, 9. Bill of quantities, and 10. Notes when there are any.

BoQ

S.No · Description · Qty · Unit · Remark: the maintenance-free earth pit, with the pit count by category in the remark; one row per GI strip size, including wastage; the Cu earthing cable; the MMS earthing connections; the serrated washers; the tracker bonding jumpers, on a tracker plant; and a test joint for each arrester's down conductor.

Exports

After a save the footer reads "Saved <path>".

How it relates to the rest of the application

• Its quantities stay in this window. Earthing materials are not in the bill of materials, the Summary, the Export ▾ menu, the layout DXF, the KMZ or the Word report. Take them from the BoQ tab and its CSV.
• Its inputs are not saved with the project. They are remembered while the application window stays open — reopening Earthing Design brings back your last values — and File ▸ New Project starts them again at the defaults. Note the values you used, or keep the PDF, which prints the key inputs.
• It works on the layout it was opened on. An open window does not follow a later Generate Layout or an edit to the layout, and is not marked out of date. After changing the layout, open Earthing Design again.

Where to go next