Earthing, lightning and surge protectors (SPD) for Malaysian homes: what the rules say and what to check

Malaysia gets a lot of lightning, and the questions in electrical groups follow the storms. Why does the house trip whenever there’s thunder? Should I add a surge protector? Is my earthing good enough? The short answers: a house’s shock protection depends on a working earth and RCCBs; a surge protection device (SPD) at the board helps against surges, but it’s one part of a system, not a cure on its own; and an earth is judged by a measured resistance in ohms, not by how many rods are in the ground.

What a home earthing system must include

The Energy Commission’s domestic wiring guideline sets out the basics:

• Malaysian homes use the TT system: TNB’s earth isn’t extended to your house, so the house has its own earth electrode, a copper-jacketed steel rod in a concrete or PVC earth chamber.
• The main bonding conductor is at least 10mm², and each circuit’s protective (earth) conductor matches the live conductor’s size up to 16mm².
• Exposed metal must be earthed: the wiring’s metal conduit and boxes, and also grilles, fences and metal roof structures. An unearthed metal frame can become live from a damaged cable without anything tripping.
• The earth electrode’s resistance must be below 200 ohms for a house protected by RCCBs, and below 10 ohms where a lightning protection system (rooftop air terminals and down conductors) is fitted.

Why is 200 ohms enough? In a TT house, an earth fault usually doesn’t draw enough current to trip an MCB, so the RCCB is what protects you. With a 200-ohm earth and a 100mA RCCB, the voltage on faulty metalwork stays around 20V before it trips. The resistance is measured with an earth-resistance tester, using spikes driven 10 and 20 metres from the rod. That’s a contractor’s job, not something a multimeter can do.

Keep the earth chamber accessible and marked so renovation work doesn’t dig through it, and never disconnect the earth cable from the rod.

Surge protectors (SPD)

An SPD sits in the DB and diverts sudden voltage spikes, such as those from nearby lightning arriving through the power cable, to earth. It doesn’t protect against a direct strike, and surges can also enter through other cables such as phone, TV and autogate wiring. ST’s guideline expects homes to be fitted with SPDs according to a lightning risk assessment under the Malaysian standard MS IEC 62305. A consulting engineer or an electrical contractor registered with the Energy Commission carries out that assessment, and it decides whether and what kind of protection is needed. In ST’s example layouts, the SPD sits after the main switch and before the RCCBs. Where a house gets one, it is usually a Type 2 SPD at the DB: 1P+N for a single-phase supply, 3P+N for three-phase. For what’s on sale in Malaysia, including types, ratings, prices and how to spot listings without a proper reference, see our SPD category page, which compares the Schneider Acti9 iPRD, Maxguard and Hager ranges.

Electricians in the groups add a practical condition: an SPD needs a good earth to discharge into. In a widely-read thread about a new house without one, the most-liked reply said they aim for an earth reading under 10 ohms before fitting an SPD. That’s a practitioner rule of thumb, stricter than the 200-ohm requirement for RCD protection, and not the same thing as ST’s 10-ohm figure for lightning protection systems. Others in the same thread pushed back: getting below 10 ohms can be expensive, they treated new-house SPDs as near-decoration, and they would put a 10mA device for the water heater first. How well an SPD works also depends on the right type and short connecting leads, not just the earth reading. The sensible order is to get the earth tested, then decide on the SPD with the contractor. Other upgrades worth doing at the same time include separate RCCBs for lighting (100mA) and sockets (30mA), and 10mA protection for water heaters (water heater guide).

“It trips every time there’s lightning”

This comes up constantly, and the experienced answer is to test before you dig. One owner had already measured their earth at about 8 ohms and added a second earth pit, yet still lost an autogate and some lights in a storm. The replies pushed for an insulation test and an RCD test rather than more earthing. Lightning-related trips can come from a surge, a corroded earth connection, small leakages that appear when things get damp, or an RCCB that has become over-sensitive. Placement matters too: an SPD wired after an RCCB sends surge current through it and can trip it in storms, which is one reason the example layout puts the SPD ahead of the RCCBs. Our RCCB tripping guide goes through how electricians narrow faults down.

How a missing earth is found

It happens more than you’d expect. One electrician found a house with no earth at all after 12 years, even though two technicians had added sockets in that time; another mentioned a three-phase house with none.

• A cheap plug-in socket tester is a useful first screen, but commenters warn they’re not always reliable, since the earth pin may not make good contact. Treat a result as a reason to call an electrician, not as proof either way.
• An electrician checks voltages and continuity. With a healthy earth there’s roughly the full supply voltage (about 230V) between live and earth and only a few volts between neutral and earth. A missing or erratic live-to-earth reading points to a missing earth. They also test the earth resistance with the proper tester. Don’t open the DB to measure it yourself.
• Tingles or small shocks from appliances mean current is leaking and its path to earth is missing or broken. Stop using the item. In one case the cause was an extension lead the owner had lengthened, with a damaged earth wire. Without an earth, leakage isn’t picked up until someone touches the metal.

A common belief in the groups is that if the RCCB’s test button doesn’t trip, the house has no earth. That’s not how it works. The test button trips the device through an internal circuit whether or not there’s an earth. A button that doesn’t trip means the RCCB is faulty or has no supply, and it should be replaced. Even a working button only shows the mechanism moves; ST’s guideline notes it can’t confirm the trip sensitivity or time, which needs an RCD tester.

If you live in a flat or apartment, the building’s lightning protection and its main earthing belong to the management corporation, so report problems there. Wiring and faults inside your unit, from your DB to your sockets, are usually the owner’s or landlord’s to fix. One resident described cutting an earth wire because it was “live”. Never do this: a live earth conductor is a fault to report, not a wire to remove.

Should a sub-DB have its own earth?

When a long house gets a second DB, for example for the kitchen, some wiremen suggest a separate earth pit for it, while others share the main earth. The groups don’t agree. One technical point from the discussion helps: an RCCB responds to the imbalance between live and neutral, not to which earth pit current flows into, so a separate earth on its own doesn’t stop trips spreading; giving the sub-DB its own RCD does. If a second electrode is used, an electrician should make sure it’s bonded or tested to meet the earth limit, so that metalwork in different parts of the house can’t sit at different voltages.