Earthing gives fault current a safe path so protective devices can switch off a dangerous circuit quickly. Learn how protective earthing and bonding work, why solar frames and rails are earthed, how inverters detect faults and why only licensed electricians do this work. Earthing is a safety system that gives electricity a deliberate, low-resistance path to follow if something goes wrong, so a fault switches a circuit off instead of leaving metal parts dangerously live. Solar panel frames and mounting rails are earthed or bonded because they are large metal surfaces sitting close to conductors that can carry DC at several hundred volts. If insulation ever fails, the earthing system is what turns a hidden hazard into a fault that protective devices and the inverter can detect.
What protective earthing actually does
Most electrical equipment has exposed conductive parts, such as a metal case, that are not meant to carry current. In normal operation they sit at zero volts. If a live conductor comes loose or insulation breaks down, that metal can become energised. Without an earth connection it may stay live, waiting for someone to touch it and become the path to ground.
Protective earthing connects exposed metal parts, through a green and yellow earth conductor, to the main earthing terminal at the switchboard and from there to an earth electrode driven into the ground. When a fault occurs, current flows through the low-resistance earth path instead of through a person, and the high fault current makes the circuit breaker or fuse operate quickly.
The MEN system and the fault loop
Australian homes use the multiple earthed neutral (MEN) system. At the main switchboard the earth and neutral are joined by a link, and the network also earths its neutral at many points along the street. Together these create a complete, low-impedance loop for fault current:
- A live (active) conductor touches a metal case or frame.
- Current flows through the protective earth conductor back to the main switchboard.
- The MEN link passes that current into the neutral, which returns it to the supply transformer.
- Because the loop resistance is low, the current is large enough to trip the circuit breaker or blow the fuse within a fraction of a second.
Residual current devices, or safety switches, add another layer. They compare current flowing out on the active conductor with current returning on the neutral and trip if the difference suggests current is leaking elsewhere, such as through a person. The protections work together, as the table shows.
| Protection | How it works | Main job |
|---|---|---|
| Protective earthing | Low-resistance path from metal parts to the earthing system | Stops metal parts staying live after a fault |
| Circuit breaker or fuse | Disconnects when current exceeds its rating | Clears high fault currents and overloads |
| Residual current device | Detects imbalance between outgoing and returning current | Cuts supply when current leaks through an unintended path |
| Equipotential bonding | Joins conductive parts so they sit at the same voltage | Prevents dangerous voltage differences between touchable parts |
| Inverter insulation monitoring | Measures DC insulation resistance and leakage current | Detects hidden insulation breakdown in the solar array |
Equipotential bonding in plain terms
Electric shock happens when a voltage difference drives current through the body. If two metal objects you could touch at the same time are at different voltages, touching both completes a circuit. Equipotential bonding connects conductive parts together, and to the earthing system, so they rise and fall together during a fault and no dangerous difference appears between them.
This is why bonding appears around swimming pools, some metal water piping and large metal structures. On a solar array, the aluminium panel frames and rails form an extended metal structure on the roof, often close to metal roofing, gutters and conduit. Bonding them keeps the whole assembly at the same potential and gives any fault a defined path.
Why solar frames and rails are earthed
A solar array is unusual because it cannot simply be switched off at the source. Whenever light reaches the panels they produce voltage, and a residential string commonly operates at several hundred volts DC. Over decades on a roof, cable insulation, connectors and panel materials face ultraviolet light, heat, moisture, wind movement and the occasional animal chewing on cables. If insulation fails where a conductor touches a frame or rail, that metal could become energised. How strings, panels and the inverter fit together is explained in how solar power works.
Australian standards for PV arrays set out when and how frames and mounting structures are earthed or bonded, along with conductor sizes and connection methods. The details matter. Aluminium frames are anodised, and the anodised layer is a good electrical insulator, so earthing hardware is designed to cut through the coating and make a reliable metal-to-metal connection. Fixings must also resist corrosion between different metals, because a connection that corrodes gradually loses its low resistance. Unfamiliar terms are defined in the solar technology glossary.
How inverters watch for earth faults
Grid-connected inverters check the insulation of the DC side, typically before they start each morning, by measuring the resistance between the array conductors and earth. If it is too low, often because of moisture in a connector or damaged cable, the inverter will not connect and reports an insulation or isolation fault. Many inverters also monitor residual current while operating. Australian requirements call for an earth fault alarm so the owner is alerted, commonly through an indicator on the inverter, a monitoring app notification or both. An earth fault message should never be ignored or repeatedly cleared, because it can indicate damaged insulation carrying DC voltage onto metalwork.
Why only licensed electricians work on earthing
In Australia, electrical work must be carried out by a licensed electrician, and solar systems must be designed and installed by an accredited installer. Earthing shows why. A missing or loose earth is invisible in normal operation; everything works until the day a fault occurs. Verifying it requires calibrated instruments and specific tests, including earth continuity, insulation resistance and polarity, performed and recorded at commissioning. For owners, the safe role is observation and reporting:
- Do not touch panel frames, rails or cables if you suspect damage, and stay off the roof.
- Treat any tingle from a tap, appliance or metal fixture as urgent and have a licensed electrician investigate.
- Report earth fault alarms and unexplained safety switch trips to your installer or electrician.
Next steps
If your system is several years old or has shown an earth fault alarm, arrange a professional inspection. The energy market lists an Electrical Safety Inspection at $299, in which a licensed electrician tests isolators, earthing, insulation resistance and RCDs, and Solar Fault Diagnosis at $249; prices are indicative and confirmed after a site assessment. For a new system designed and installed to current standards, request a free assessment from Blue Energy Solar.
Frequently asked questions
Does earthing the panels protect a house from lightning?
Not in the way many people assume. Frame earthing is designed for electrical safety during insulation faults, not to carry a direct lightning strike, which would need a separately engineered lightning protection system. Direct strikes on houses are uncommon, and damage more often comes from surges induced by nearby strikes. Surge protective devices at the switchboard and on solar circuits can reduce that risk where they suit the installation.
Why does a safety switch sometimes trip after heavy rain?
Water can find its way into outdoor power points, isolators, junction boxes or damaged cables, creating a small leakage path that the residual current device detects. The switch is doing its job. Resetting it repeatedly without finding the cause is not safe. Note which circuit trips and when, then have a licensed electrician trace the fault, because moisture-related leakage often worsens over time.
Is the main earth checked when solar is installed?
Electricians test the earthing of the new work they install and connect, and while working at the switchboard they will often notice obvious problems with the existing main earth, such as a loose or corroded connection. A full assessment of an older installation is a separate inspection. If your home has original wiring or several additions over the decades, it is worth requesting that check.
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