In an earthed system, the neutral point of a generator or a transformer is directly connected to earth with no deliberate resistance or reactance between. No buffers, a direct connection. Any fault between phase and earth is instantly apparent to the system, and protective devices such as fuses or circuit breakers can promptly trip to disconnect the problem.

A nice example is a standard 400V three-phase supply to a commercial building in Sydney. The local distribution transformer’s neutral is directly bonded to the earth electrode at the main switchboard, providing a low-impedance path to ground. If there is a fault—i.e., if someone accidentally drills through a wall and into a phase conductor—the circuit breaker will trip virtually instantaneously, switching off power and avoiding danger to humans.

Why We Use It

The attraction of solid neutral earthing is quite straightforward. Faults are easy to identify. When there is a phase-to-earth fault, the fault current is high—typically many kiloamps based on the installation. The large current allows it to be easy to make protective devices act. No sophisticated detection schemes or special equipment needed.

Consider, for example, a shopping centre in Melbourne with a distribution board. Suppose one of the light circuits gets faulty—such as insulation failure in a cable that traverses above the ceiling. The high fault current goes directly to earth through the solidly earthed neutral. The MCB easily trips immediately, avoiding fire or overheating.

How It Helps Maintain Voltage Stability

Another significant benefit is voltage stability. In neutrally earthed systems, the healthy phases do not drop their normal line-to-earth voltage even under fault conditions. This decreases the insulation stress and electrical equipment stress, reducing the chances of cascading failures.

Let’s say we’re dealing with an industrial facility in Perth with multiple three-phase motors. If one phase develops a fault to earth, the other phases won’t suddenly jump in voltage or cause unexpected damage to the motors. The solid earthing stabilises everything while the protection trips out the faulty circuit.

Fast Fault Clearing with Minimal Fuss

One of the major advantages we have from solid neutral earthing is the ease of protection. Overcurrent protective devices such as MCBs and MCCBs can identify faults with ease since the fault current is high and unequivocal. That makes protection device coordination in a distribution system much easier.

That’s precisely what occurs in the majority of domestic installations throughout Australia. The neutral is earthed at supply—typically within the main switchboard via a MEN (Multiple Earthed Neutral) connection. Therefore, if a metal item is inadvertently dropped into a power point and it touches the live conductor, the RCD or circuit breaker will trip instantly. That’s a classic case of robust neutral earthing performing as it should.

Where We Normally Find It

In Australia, we normally find solid neutral earthing in low-voltage installations such as 230/400V distribution boards, control panels, and service mains. It is particularly common in TN-C and TN-S systems, where the neutral is earthed at the source or along the path of distribution.

A good example is a temporary supply of power for a construction project in Brisbane. The temporary switchboard features a distribution transformer solidly earthed at its neutral. This provides stable, safe power to tools and equipment—even in the harsh conditions of a construction site.

But There Are Trade-offs

Now, solid neutral earthing is good and stable, but it’s not flawless. Its greatest drawback is precisely the reason it works so well—those high fault currents.

In the event of a fault, the current can be so high it places heavy mechanical and thermal stress on conductors, switchgear, and busbars. If that equipment isn’t rated correctly or well maintained, that stress might result in early failure.

This may occur in older buildings where switchgear has not been updated to keep up with contemporary demand. Suppose an Adelaide office has a neglected switchboard using old breakers. A minor fault may have more damage than intended, because of the high fault energy of a solidly earthed system.

Touch Voltage and Personnel Safety

Another point we must be mindful of is touch voltage. Under an earth fault, conductive items that are grounded (such as switchboard frames or metal enclosures) will increase in voltage briefly until the fault clears. If the earth path has high resistance, that voltage may be hazardous.

For instance, in a rural station along Wagga Wagga, a faulty earth electrode installation could imply that the fault current fails to flow as it should. That would leave exposed metal components to reach voltages capable of delivering a nasty shock. That’s why earth testing and maintenance are critical in solid earthed systems.

No Fault Ride-Through

One of the reasons we may not use solid earthing is when service continuity is essential. In a solidly earthed system, a phase-to-earth fault causes instantaneous disconnection. That’s the most secure option, but the system is not permitted to “ride through” the fault.

Consider an example like that of a data centre located in Canberra. If uptime is imperative, we wouldn’t want the whole system to shut down due to just one fault in its insulation. Under such circumstances, even though it presents additional complexity and expense, it could better be suited to high-resistance grounding.

Comparing Solid Earthing with Other Methods

For now, let us briefly compare solid earthing with some of the other methods you’ll see in practice.

In a Darwin apartment complex, solid earthing guarantees the reliability of RCDs and disconnects faulty circuits immediately.

At a Western Australian mine site, resistance earthing may be employed to restrict fault currents and minimize arc flash risks underground.

In certain off-grid generator installations way up north, ungrounded or impedance-earthed configurations may be employed to maintain the generator in operation even when there is a single earth fault—since continuity trumps immediate disconnection.

Both approaches are suitable in their own right, but for simplicity’s sake, ease of protection, and low-voltage system safety, solid earthing continues to be the first choice.

Installation Best Practices

To make the most of solid neutral earthing, we must fit it properly. That includes having a solid, corrosion-free neutral-to-earth connection that is easy to inspect. Several earth stakes or an appropriately sized earth grid may be necessary to provide the desired earth resistance levels.

In a commercial warehouse in Hobart, for example, there is an unoccupied earth bar that hooks up direct to multiple copper-clad ground rods that are driven into the soil. Such an arrangement ensures reliable earthing systems that can handle faults safely without introducing voltage rise hazards.

Also, do not forget equipotential bonding. All conductive parts in exposure should be bonded together and to the main earthing terminal. This minimizes the danger of voltage differences that might injure people or damage equipment in case of a fault.