What size earth wire for house wiring in Pakistan?

What does the earth wire in a house actually do?

Every circuit in the house has a live wire that carries current in and a neutral that carries it back. The earth wire carries nothing in normal use. It connects every metal part a person can touch — the geyser tank, the AC chassis, the washing machine body, the earth pin of every socket — to the ground itself. The day insulation fails and a live conductor touches a metal case, the earth gives that fault an easy path away, the current jumps, and the breaker trips in a fraction of a second. Without an earth, the case simply sits at 220 V and waits for a hand.

That is why the earthing cable size in Pakistan is set by the wire it protects, not by the load on the circuit. The earth never carries the appliance's current; it carries the fault current, which for that fraction of a second can be far larger than anything the circuit sees in normal service. So the earth is sized against the live conductor — and the rule for doing it is short enough to memorise.

Earth wire size for house circuits, size by size

In Pakistani house wiring, the minimum earth wire size follows the line conductor it protects. Up to 16 mm², the earth conductor is the same size as the line conductor. From 16 mm² up to 35 mm², a 16 mm² earth is enough, and above 35 mm² the earth may be half the line size. So a 1.5 mm² light circuit takes a 1.5 mm² earth, a 2.5–3 mm² socket circuit — the wire Pakistani shops sell as 7/29 — takes a 2.5–3 mm² earth, a 4 mm² air conditioner circuit takes a 4 mm² earth, and a 25 mm² or 35 mm² submain takes a 16 mm² earth. That is the tabulated convention BS 7671 uses when the earth conductor is the same metal as the line conductor; an electrician can calculate a smaller size from fault current and disconnection time, but the sizes above are the safe default.

Read the third column as a floor, not a target — an earth bigger than the minimum is never a fault, an earth smaller than it always is. And note what the rule implies for shopping: for every final circuit in a house, the earth is simply another core of the same wire, which is why 3-core cable such as 4mm 3 core standard cable solves the question by construction. Choosing the line sizes themselves is the other half of the job — that is the best wire for house wiring guide.

Earthing wire size with breaker rating

A breaker never sizes the earth directly. The breaker protects the live wire, so the live wire must be rated above the breaker; the earth then follows the live wire by the rule above. The chain is breaker → line → earth, and for the circuits a Pakistani house actually has, it lands like this.

Two things follow from the chain. First, when a long run forces the line up a size for voltage drop, the earth goes up with it — the rule tracks the wire actually installed, not the breaker. Second, the table assumes the breaker matches the line in the first place; a 20 A breaker on 1.5 mm² wire is a fault of its own, and the wire size too small guide shows how it ends.

Earth wire or earth rod — which one are you buying?

A house earthing system is two different purchases, and they get confused on the phone daily. The earth wire — green or green/yellow insulated copper — runs with the circuits and gathers every metal part onto one conductor. The earth rod is the electrode: a rod driven into the ground in a pit near the meter, commonly packed with salt and charcoal in Pakistani practice, that gives the fault its final exit into the soil. We manufacture the wire; the rod, the clamp and the pit materials come from the hardware market.

The run from the distribution board to that rod — the main earthing conductor — follows the same sizing rule, applied to the biggest line conductor in the house: the meter tails. Tails of 10 mm² take a 10 mm² earth, tails of 16 mm² take 16 mm², and 25 or 35 mm² tails take 16 mm² under the over-16 rule. Pakistani practice often runs 6 mm² to the rod on a 10 mm² main — an adiabatic calculation can justify it, and the marla cable lists reflect that practice — but the tabulated size is the conservative default. That is why most houses land between 6 and 16 mm² for the rod run, and it is the job our earth cable range — 6, 10 and 16 mm², up to 35 mm² — is drawn for.

A solar array on the roof raises its own earthing questions — panel frames, inverter, the DC side — and has its own guide: solar earthing cable size.

Why does "earth through the conduit" fail?

A shortcut some wiring jobs take: skip the earth core and let the conduit carry the fault — the pipe is metal, the theory goes, and it reaches every box. It fails for reasons visible on any site. Most house conduit in Pakistan is now PVC, which is an insulator: there is no path at all, only the look of one. Where the conduit really is steel, the path depends on every threaded joint staying tight, unpainted and unrusted for the life of the building, and it breaks silently the day a coupling is disturbed or a plastic box is spliced into the run. Nobody tests it afterwards, so nobody knows.

The other version of the shortcut is the empty earth pin — 2-core cable run to a 3-pin socket. The socket looks finished, the earth terminal connects to nothing, and every metal-bodied appliance plugged in there is floating. An earth is a continuous copper conductor of its own, terminated at both ends, all the way from the appliance to the rod. Anything less is a drawing of an earth.

Worked example: what earth does a 7/29 socket circuit need?

Take the commonest circuit in the country: sockets wired in 7/29 — seven strands of 0.029 inch, which computes to about 3.0 mm² and is sold as 2.5–3 mm². The line is under 16 mm², so the earth matches it: 2.5–3 mm², which in practice means the same 7/29 in green/yellow from the general wiring range, or the third core of a 3-core cable.

The size matters because the earth is half of the fault loop. Taking the 2.5 mm² class 2 figures, resistance is 7.41 Ω/km, so a 20 m run puts 20 × 7.41 ÷ 1000 = 0.148 Ω in the live leg and, with a matching earth, the same 0.148 Ω in the return — 0.296 Ω of cable in the loop. Drop the earth one size to 1.5 mm² at 12.1 Ω/km and the return leg alone becomes 20 × 12.1 ÷ 1000 = 0.242 Ω, and the loop rises to 0.390 Ω — a third more. A higher loop resistance means a smaller fault current and a slower trip, and a fast trip is the entire reason the earth exists.

On a rod-earthed house the pit's own resistance sits on top of both figures, and usually dominates them — which is why the pit is maintained, not just dug, and why an RCD or ELCB in the board is worth having alongside the earth, never instead of it.

Earth cable from the Lahore factory

For circuit earths up to 16 mm² the answer is usually already in the cable: take 3-core, or add a green/yellow single from the general wiring range at the same size as the line. For the main earthing conductor — the board-to-rod run — we draw a dedicated earth cable range, 6 to 35 mm², class 2 stranded copper, on the Pilone line in Lahore, from a family in the copper trade since 1992.

The other sizes: 10mm² earth cable and 16mm² earth cable for most house rod runs, 25mm² and 35mm² for panel and industrial earthing.

Frequently asked