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A surge arrester is a critical protective device installed in electrical systems to safeguard equipment from voltage spikes. These spikes can originate from multiple sources.
Lightning strikes are the most dramatic source. Approximately 100 lightning strikes hit Earth's surface every second. Even indirect strikes near power lines can induce massive voltage surges.
Switching operations creates surges, too. When large motors start, transformers energise, or circuit breakers operate, they generate transient overvoltages that propagate through the system.
Grid disturbances from faults or equipment failures can send voltage spikes rippling through connected installations.
Studies show that 50-70% of transformer failures are caused by low-side surges. Installing secondary surge arresters can reduce transformer failure rates by an order of magnitude, making them essential for protecting expensive equipment investments.
Surge arresters work by providing a low-resistance path to earth when voltage exceeds safe levels. Once the surge passes, the device returns to its high-resistance state, allowing normal operation to continue.
The difference between a surge arrester and standard circuit protection is response time. Circuit breakers and fuses react to sustained overcurrent in milliseconds. Surge arresters respond to voltage spikes in microseconds, protecting against transients that would pass right through conventional protection.
Modern surge arresters rely on metal oxide varistor (MOV) technology. This is fundamentally different from the gap-type arresters used in older installations.
An MOV acts as a voltage-controlled switch. At normal operating voltage, it presents extremely high resistance, drawing virtually no current. When the voltage exceeds the rated threshold, the resistance drops dramatically, creating a path to earth for surge current.
The MOV block consists of zinc oxide grains bonded together. Each grain junction acts as a microscopic diode. At low voltage, these junctions block current flow. At high voltage, they conduct freely.
This happens in microseconds. From the moment a surge appears until the MOV diverts it to earth, it takes less time than a single cycle of AC power.
MOV arresters have replaced older gap-type designs for several reasons:
Gap-type arresters had spark gaps that required periodic inspection. Environmental contamination could affect their operation. MOV arresters are sealed units requiring no maintenance until replacement.
The voltage protection level (VPL) indicates the maximum voltage that will appear across protected equipment during a surge. Lower VPL values provide better protection. Select arresters with VPL ratings compatible with your equipment's withstand capability.
Surge arresters are classified by application and surge current capacity. Understanding these classifications helps specify the right protection for your installation.
Station class arresters protect substations and major switchgear. These are the highest-rated devices, designed for direct lightning strikes and severe switching surges.
Intermediate arresters bridge the gap between station and distribution class protection. Common in commercial and industrial installations.
Distribution class arresters are the most common type in Australian installations. Found in residential and light commercial applications.
Secondary arresters provide point-of-use protection for sensitive equipment. These are the final line of defence in a coordinated protection scheme.
The terms "surge arrester/surge protection device" and "lightning arrester" are often confused. While related, they serve different purposes in electrical protection.
Lightning arresters, properly called air terminals or lightning rods, are structural protection devices. They provide a preferred path for lightning to strike, directing energy safely to earth via down conductors.
These systems prevent direct strikes to buildings but don't protect electrical equipment from induced surges. That's where surge arresters come in.
Surge arresters/Surge protection devices protect electrical systems from transient overvoltages. They're installed within the electrical distribution system, not on the building structure.
Surge arresters handle both lightning-induced surges and switching transients. Their protection isn't limited to lightning events.
Structurally protected buildings still require surge arresters. Lightning striking a roof-mounted rod induces strong electromagnetic fields inside the building. These fields couple into electrical systems, creating surges that only surge arresters can handle.
AS/NZS 3000:2018 uses the term "surge protection device" (SPD). This aligns with international standards and clearly distinguishes electrical protection from structural lightning protection.
Older documentation may use "surge arrester" or "lightning arrester" interchangeably. In modern practice, SPD is the preferred term for electrical protection devices.
Proper placement of surge arresters is critical for effective protection. A coordinated protection scheme uses multiple arresters at strategic locations.
The primary SPD is installed at the main switchboard, as close as possible to the incoming supply. This protects the entire installation from externally generated surges.
Secondary protection at distribution boards captures surges that pass the main SPD or are generated within the installation.
Final protection installs immediately before critical or sensitive equipment. This provides the tightest voltage clamping for electronics.
Keep all SPD connections as short as possible. Every metre of lead adds inductance, increasing the voltage spike at protected equipment. AS/NZS 3000 specifies maximum lead lengths for SPD installations.
Certain installations require additional attention:
Solar PV Systems: Install SPDs on both DC and AC sides. DC-rated arresters are required for array protection.
Rural Installations: Overhead supply lines are more susceptible to lightning. Multiple protection stages are essential.
Medical Locations: Patient safety areas require careful SPD coordination to maintain supply continuity.
Industrial Sites: Large motor loads generate switching surges. Protect sensitive control equipment separately.
Choosing the correct surge arrester involves several technical considerations. Get it wrong, and you risk either inadequate protection or nuisance tripping.
The surge rating must match your installation's exposure. Urban areas with underground supply can use lower ratings. Rural overhead supplies need higher capacity.
For most domestic supplies in urban environments, a surge rating of 20 kA to 40 kA is adequate. However, it's prudent to install SPDs with higher ratings (65 kA to 100 kA per phase) in areas with frequent lightning activity or overhead supply lines.
Match the arrester poles to your supply configuration:
In TN-S systems, neutral protection may not be required at main switchboards. In TT systems or when neutral integrity is questionable,four-pole protection is recommended.
The continuous operating voltage (Uc) must exceed the maximum continuous voltage the arrester will see. For 230V single-phase systems, select arresters rated at 275V Uc minimum.
For three-phase 400V systems, use arresters rated for 440V Uc or higher to account for voltage variations and neutral displacement.
Multiple SPDs must coordinate to ensure the most capable device handles each surge. This prevents lower-rated devices from failing prematurely.
Manufacturers provide coordination tables showing compatible SPD combinations. Follow these recommendations carefully.
Select arresters with visual indicators or remote status signalling. This allows monitoring without testing.
Replaceable cartridge designs simplify maintenance. The base remains wired, and cartridges can be swapped in seconds.
| Application | SPD Type | Surge Rating | Location |
|---|---|---|---|
| Residential (urban) | Type 2 | 20-40kA | Main switchboard |
| Residential (rural) | Type 1+2 | 65-100kA | Service entrance |
| Commercial | Type 1+2 | 40-65kA | Main + distribution |
| Industrial | Type 1+2+3 | 65-100kA | Multiple stages |
| Sensitive equipment | Type 3 | 8-20kA | Equipment inlet |
These surge protection devices are proven performers in Australian installations. Each product link opens in a new window for your convenience.
NLS 30539 Surge Arrester 1-Pole 20kA 275V provides cost-effective single-phase protection. Ideal for residential applications with underground supply. DIN rail mounting fits standard switchboards.
Clipsal MX9SP140 MAX9 SPD 1P 40kA steps up capacity to 40kA. Suitable for single-phase supplies with overhead lines or high lightning exposure. The visual indicator shows the protection status.
Hager SPB140D 1-Pole 40kA with Replaceable Cartridge offers the same capacity with easier maintenance. Cartridge replacement takes seconds without rewiring.
Clipsal MX9SP40C MAX9 SPD Cartridge fits the Clipsal base units. Keep spares on hand for immediate replacement after surge events.
NLS 30719 3-Pole SPD 40kA protects three-phase installations. Compact design saves switchboard space while providing comprehensive protection.
Clipsal MX9SP340 MAX9 SPD 3P 40kA brings Clipsal quality to three-phase systems. Proven reliability in commercial installations.
Hager SPB165R 1-Pole 65kA handles severe exposure conditions. Use where lightning strike frequency is high, or supply lines are extensive.
Hager SPB408D 4-Pole TN-S/TT 8kA provides complete protection, including neutral protection. Essential for TT earthing systems or where neutral integrity must be assured.
Our technical team can recommend the right surge protection for your installation
View Full RangeSurge arrester installation in Australia must comply with AS/NZS 3000:2018 Electrical Installations (Wiring Rules). While this standard doesn't mandate SPD installation in all cases, it provides comprehensive guidance when SPDs are used.
The Wiring Rules address surge protection in Clause 2.7 and Appendix F. Key requirements include:
Appendix F provides detailed guidance on SPD selection and installation. This informative appendix is not mandatory but represents industry best practice.
AS/NZS 3000:2018 notes that surge protection is not mandated for all installations. However,a risk assessment should determine whether protection is needed.
Factors to consider include:
Where structural lightning protection (lightning rods) is installed, AS/NZS 3000:2018 requires primary surge protection at a minimum. The electromagnetic effects of lightning striking the structure necessitate electrical protection even with proper earthing.
Surge arresters must comply with product standards for safety and performance:
Products certified to these standards ensure proper coordination and compliance with safety standards.
All surge arrester installation work must be performed by licensed electricians. This ensures:
DIY installation voids product warranties and may breach electrical safety regulations.
After installation, verify SPD operation:
Regular inspection ensures continued protection. Replace SPDs according to manufacturer recommendations or after major surge events.
Learn more by watching our NLS 30539 | Surge Arrestor 1 Pole 20ka 275V | SPD1R video
Learn more by watching our Clipsal MX9SP140 | MAX9 SPD 1P 40kA Surge Protection Device video
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We all spend a fortune insuring our home and vehicles. Installing a surge protection device is great insurance and affordable when you consider it protects thousands of dollars of electronic equipment (TV's, Entertainment equipment, Oven, Dishwasher, Washing Machine, Items such as phones & devices connected to chargers) within your home -should a surge in voltage occur.
I bought products from Sparky Direct several times. Every time the products were shipped fast and I had no issues. I like the website with its easy navigation. Pricing is also good
Can't beat Hager products, better to be safe then sorry
Browse our complete range of surge arresters from Clipsal, Hager ,and NLS
Shop Surge ArrestersGet Technical AdviceFor urban areas with underground supply, 20-40kA SPDs are adequate. Rural properties with overhead lines require 65-100kA surge protection. Industrial sites and lightning-prone areas need 100kA rated devices.
Type 1 SPDs (65kA+) install at service entrance for direct lightning protection.
Type 2 SPDs (20-40kA) protect distribution boards from switching surges.
Type 3 SPDs (8-20kA) provide point-of-use protection for sensitive equipment.
Replace SPDs immediately after major surge events or when status indicators show failure. Devices with visual indicators should be inspected quarterly. Manufacturers typically recommend replacement every 5-10 years depending on surge exposure and usage.
Yes, one properly rated SPD installed at a distribution board protects all circuits downstream from that board.
However, sensitive equipment benefits from additional dedicated SPDs installed at the equipment location.
Yes, solar PV installations require surge protection on both DC (array side) and AC (grid side) circuits. Use DC-rated SPDs for array protection and standard AC SPDs for the grid connection.
Solar photovoltaic systems are particularly vulnerable to lightning and switching surges. The large array area acts as a lightning collector, while the inverter contains sensitive electronics.
AS/NZS 3000:2018 does not mandate SPDs for all installations but requires them when structural lightning protection exists.
A risk assessment determines whether protection is needed based on lightning exposure, supply configuration, and equipment value.
Australian Wiring Rules take a risk-based approach to surge protection rather than universal mandatory installation.
AS/NZS 3000:2018 covers SPD installation in Clause 2.7 and Appendix F.
Key requirements include connecting to the main earthing terminal, minimising lead lengths, providing disconnection means, and coordinating overcurrent protection with SPD ratings.
The Wiring Rules provide comprehensive guidance on surge protection device installation.
Clause 2.7.3 - Basic Requirements:
Appendix F - Detailed Guidance:
Installation Location:
Overcurrent Protection:
Lead Length Critical:
Status Indication:
Labeling:
Connection Points:
Yes, all surge protection device installation must be performed by licensed electricians in Australia.
SPD work involves main switchboard connections, overcurrent device coordination, and compliance with AS/NZS 3000:2018 - all requiring electrical licensing.
Unlicensed electrical work carries significant penalties:
All three brands meet Australian Standards.
Clipsal offers an extensive product range and Club Clipsal rewards.
Hager provides replaceable cartridge designs for easier maintenance.
NLS delivers cost-effective protection for budget-conscious projects.
Choose based on specific features, budget, and maintenance preferences.
Replaceable cartridge SPDs have a permanent base unit and a removable protection element.
When the SPD fails, replace only the cartridge (30 seconds) rather than rewiring the entire device (15 minutes).
This reduces maintenance time by 95% and labour costs significantly.
SPDs have visual indicators that indicate the protection status.
Green typically means operational, red indicates failure.
Some models include remote alarm contacts.
Failed SPDs may also show physical signs like discolouration, melting, or a burning odour.
No, properly installed SPDs should not cause nuisance RCD tripping.
Install SPDs after the main switch but before RCDs as specified in AS/NZS 3000:2018.
If an RCD trips, check for earth leakage at the SPD or for incorrect installation.
Yes, surge protection provides excellent ROI.
A $350 residential SPD installation protects thousands of dollars in electronics.
Commercial installations save tens of thousands in equipment replacement and downtime costs.
Insurance claims and equipment warranties often require surge protection.
Yes, Sparky Direct provides free technical support for surge protection selection.
Our team helps licensed electricians choose appropriate SPD ratings, brands, and configurations.
Contact us for project-specific recommendations, coordination guidance, and product availability.
