What size is the ground wire?

The home's grounding electrode conductor is copper of at least 10 sq.mm, sized up with the main wire. The per-circuit ground is chosen by breaker rating (e.g. ≤20 A → 2.5 sq.mm, ≤40 A → 4 sq.mm) per the EIT table; for larger ratings, have an electrician pick from the full table.

If I have an RCD, do I still need a ground wire?

Yes — they complement each other. Grounding is the drain for leakage; the RCD is the watchdog that cuts power on an imbalance. Having a ground makes the RCD act faster and more reliably. An RCD does not replace grounding.

How deep is the ground rod, and what earth value passes?

A standard rod is at least 2.4 m long and at least 16 mm across, driven into the soil, with a total earth resistance of no more than 5 ohms. In dry soil where the value is too high, several rods or an earth-resistance-reducing compound may be needed.

Can I install grounding myself?

You can do basic checks (use genuine three-pin outlets, plug in three-pin appliances, never cut the earth pin), but installing the system, driving the rod and measuring the earth value should be done by a licensed electrician, since conductors must be sized from the EIT table and the utility inspects before energising — ask MEA 1130 / PEA 1129.

There's voltage on my ground wire — is it dangerous, and what should I do?

Yes — a ground wire should normally carry no voltage relative to earth. Typical causes are swapped wiring, a floating ground that never reaches an earth rod, or a leaking appliance combined with high earth resistance. Stop using that socket/appliance, switch the circuit off and have a licensed electrician inspect. A faint glow on a test screwdriver can come from induction, so it screens but cannot confirm.

Is a "ground wire" the same as an earth wire? What size is it?

Yes. "Ground" (also "earth") is the same green-and-yellow conductor to earth, so the same sizing applies as in the table on this page: at least 10 sq.mm for a typical home's grounding electrode conductor, and circuit grounds sized by breaker rating (≤ 20 A → 2.5 sq.mm, ≤ 40 A → 4 sq.mm) per the EIT standard.

Home Electrical Safety

What Is a Ground Wire, and Do You Need It? What Size, and How to Connect

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A ground wire (the green-yellow one) bonds an appliance's metal body to earth so any leakage current flows safely to ground instead of through a person who touches it. This page answers what a ground wire is, why it matters (especially for water heaters and washing machines), how dangerous it is to go without one, what size to use, how deep a ground rod is driven, and how grounding differs from an RCD (earth-leakage breaker) — based on EIT and utility standards.

7 min readLast updated: 4 October 2026Standard: EIT standard · MEA/PEA

A ground wire is the (green-yellow) conductor that bonds an appliance's metal body and the home's electrical system down to a “ground rod” driven into the earth. Its job: if current leaks to the metal casing, it flows to earth through the ground wire and makes the breaker / earth-leakage device trip, instead of waiting to pass through the person who touches it. It is essential — especially for water heaters, washing machines and metal-bodied appliances in wet areas. Typical sizes: the home's grounding electrode conductor is at least 10 sq.mm (chosen by main-wire size per the EIT table), the ground rod is at least 2.4 m long, and the earth resistance must be no more than 5 ohms. Actual installation should be done by a licensed electrician and inspected by the utility before use.

In Short: What a Ground Wire Is, Which Size, and Whether You Need One

The five core questions in one table (all figures come from the EIT reference table further down — the actual size is chosen on site by an electrician):

In Short: What a Ground Wire Is, Which Size, and Whether You Need One
Question	Answer
What is it?	The green-and-yellow conductor (also called the ground or earth wire) that connects appliance metal casings and socket earth terminals to an earth rod driven into the ground.
What does it do?	It gives leakage current a path to earth instead of through a person, and helps the protective device disconnect the circuit.
Which size?	Grounding electrode conductor for a typical home ≥ 10 sq.mm · circuit ground: breaker ≤ 20 A → 2.5 sq.mm, ≤ 40 A → 4 sq.mm (larger per the EIT table).
Earth rod	Copper or copper-clad steel, ≥ 16 mm diameter, ≥ 2.4 m long, earth resistance ≤ 5 Ω.
Do I need it?	Yes — especially for water heaters, washing machines and metal-bodied appliances in wet areas — and it should work together with an RCD, not instead of one.

What Is a Ground Wire and Why Have One?

A ground (earth) wire creates a “short path to earth” for any current that escapes the normal circuit. In practice it runs from the earth pin of outlets and the metal body of appliances, to the ground bus in the main panel, then down to a ground rod driven into the soil. When insulation inside a device degrades and current leaks onto the casing, the ground wire carries it straight to earth, making the protective device (breaker / RCD) cut the power so the casing never rises to a dangerous voltage — which is why grounding is a “life-safety system,” not something that makes the appliance run better.

Is a Ground Wire Necessary? What Happens Without One?

Very necessary — and even more so anywhere with water or damp. Without a ground wire, when current leaks to a metal casing these problems follow:

The casing stays live, waiting to be touched: the metal body becomes a conductor holding a voltage; anyone who touches it (especially with wet hands or on a wet floor) becomes the path to earth — an electric shock that can be fatal.

The protective device may not trip, or trip late: an ordinary breaker is built to trip on overcurrent or a short circuit. With no ground path to complete the leakage circuit, the leak current may be too small to trip it — so the casing stays energised.

A chronic leak wastes power and risks fire: a leak that never gets cut keeps flowing, raising the bill and creating a heat-buildup / fire risk (for leakage and the electricity bill, see the electrical-leakage page).

What Size / Number Is the Ground Wire?

There isn't one single size — it is chosen by function and system size per the EIT standard: the grounding electrode conductor (from the main panel to the ground rod) for a typical home is copper at least 10 sq.mm, sized up with the main wire. The equipment grounding conductor (the ground in each circuit/outlet) is chosen by that circuit's breaker rating. Reference values in the table:

Reference ground-wire and ground-rod sizes per EIT / utility standards
Item	Standard value
Ground rod — diameter	≥ 16 mm (5/8 in)
Ground rod — length	≥ 2.4 m
Earth resistance (after driving)	≤ 5 ohms
Grounding electrode conductor (typical home)	≥ 10 sq.mm (by main-wire size)
Equipment ground · breaker ≤ 20 A	2.5 sq.mm
Equipment ground · breaker ≤ 40 A	4 sq.mm
Equipment ground · larger breakers	per full EIT table — have an electrician size it

The table values are reference figures from the EIT standard for typical homes; the real size depends on the main wire, breaker rating and installation detail — have a licensed electrician pick from the full table rather than guessing (for main-wire/meter sizing see the meter & main-wire size page).

How Deep Is the Ground Rod, and How Is It Connected?

The ground rod is a copper (or copper-clad steel) rod at least 16 mm across and at least 2.4 m long, driven fully into the ground; the grounding electrode conductor then runs from the ground bus in the main panel to the rod head via a standard clamp/connector. The target is a total earth resistance of no more than 5 ohms. In dry or sandy soil the value can exceed that, so several rods or an earth-resistance-reducing compound may be needed. Every joint must be tight and rust-free — and do not use a water pipe in place of a ground rod, since these are mostly PVC today.

Most housing estates and condos already provide a building grounding system; the homeowner's job is to use genuine three-pin outlets with a live earth pin and plug in three-pin appliances — never cutting off the earth pin or using a 3-to-2-pin adapter.

Voltage on the Ground Wire (Tester Lights Up on the Earth Pin): Causes and Danger

Normally a correctly grounded earth terminal or casing should have no voltage relative to earth. If a test screwdriver lights up clearly on a socket's earth hole or an appliance casing, treat it as abnormal and dangerous until an electrician checks it. Possible causes:

Voltage on the Ground Wire (Tester Lights Up on the Earth Pin): Causes and Danger
Possible cause	What it means
Wires swapped	The live wire (L) has been connected to the earth terminal of a socket or plug by mistake — very dangerous: the appliance casing becomes live the moment it is plugged in.
A "floating" ground with no real earth connection	The socket has three holes but the earth wire never reaches an earth rod, so when one appliance leaks, the voltage sits on the whole circuit's earth system.
A leaking appliance + high earth resistance	Leakage from an appliance flows into the earth wire, but the earth resistance is too high for it to drain away properly.
Tester glows only faintly	A test screwdriver can glow faintly from induction, so it can screen but cannot confirm — have an electrician measure with a proper instrument.

Do this now: stop using that socket/appliance, switch off the related circuit breaker, never touch metal casings with wet hands, and have a licensed electrician inspect. If leakage is the cause, read earth leakage & high bills, and for leakage vs short circuit see what causes a short circuit.

Grounding vs an RCD (Earth-Leakage Breaker): What's the Difference, Do I Need Both?

They do different, complementary jobs: grounding is the “drain” that lets leakage flow safely to earth, while an RCD/RCBO (residual-current device) is the “watchdog” that checks whether the current going out equals the current coming back — if they differ, current is leaking somewhere and it cuts power within a fraction of a second. You should have both — grounding lets the RCD act faster and more reliably, and if a person touches a live part directly, the RCD is the layer that trips in time. An RCD is not a substitute for grounding, and grounding alone does not cut the power without an RCD/breaker alongside it.

Note: this page is about the grounding system itself. For how to “check whether there is a leak” and how leakage inflates the bill, see the electrical-leakage page; and if the problem is voltage sag/surge (a different topic from leakage), see the home voltage sag & surge page.

How to Tell if Your House Really Has a Ground (4 Look-Don't-Touch Checks)

All four are visual screening checks — never open the consumer unit or touch terminals yourself:

How to Tell if Your House Really Has a Ground (4 Look-Don't-Touch Checks)
Where to look	What tells you
Sockets	Three holes (the third is earth) — but three holes do not prove a real ground: some older homes swapped in 3-hole sockets without running an earth wire.
Consumer unit (through the cover)	An earth bar with several green-and-yellow wires landed on it, and one heavier conductor leaving the unit.
Earth rod outside	A rod head at ground level near the meter or main panel, with a conductor from the panel clamped to it.
Plug-in socket tester	A plug-in device with indicator lights that screens whether earth is connected or wires are swapped — confirm any abnormal result with an electrician's measurement.

Confirming that the grounding system actually works (including measuring earth resistance) needs a licensed electrician's measurement — utilities: MEA 1130 / PEA 1129.

Can I Install a Ground Wire Myself?

You can understand the principle and do basic checks yourself (e.g. confirm an outlet's earth pin is genuinely connected, use three-pin plugs), but installing the grounding system, driving the ground rod and measuring earth resistance should be done by a licensed electrician — it requires sizing conductors from the EIT table, making standard-grade tight joints, and getting the earth value within limits. The utility also inspects wiring before energising a new meter, so bad connections or a failing earth value are both unsafe and likely to fail inspection — ask MEA 1130 / PEA 1129.

About the Author

Compiled by the CapSolar team under Frank Lee (Founder). CapSolar is a commercial & industrial solar EPC/PPA provider in Thailand that distils electrical standards and safety guidance from official sources (EIT / the utilities). This article is general information — real grounding installation should be done by a licensed electrician.

FAQ

Yes — especially for water heaters, washing machines and metal-bodied appliances in wet areas. With no ground and a leak to the casing, the person who touches it becomes the path to earth — a shock. Have a licensed electrician install grounding and add an RCD.

Wire Colour Code (TIS 11-2553)

The ground is the green-yellow wire.

Electrical Leakage & High Bill

How to check a leak & who pays.

Home Voltage Sag & Surge

Voltage problems — a different topic.

Water Heater Electricity Cost

The appliance that must always be grounded.

Standard Wiring & Grounding: the Base of Safe Solar

Factories and commercial buildings adding solar need standard-compliant grounding and wiring before grid connection. CapSolar designs and installs to EIT / utility standards, with a free assessment from your actual electricity bill.

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