What is a Surge Protective Device (SPD)?

A Surge Protective Device (SPD) is an electrical device designed to protect electrical equipment from transient overvoltage. These overvoltages are typically caused by lightning strikes or switching operations and can damage or degrade electrical and electronic systems.

The main purpose of an SPD is to limit the overvoltage to a safer level for the equipment. By doing so, it ensures the longevity and reliability of electronic devices and reduces downtime and maintenance costs.

Surge Protective Devices (SPDs) can be used to help protect an electrical installation and its connected equipment from the potentially harmful effect of transient overvoltages.

There are three common types of SPD:

- Type 1 SPD installed at the origin, for example, main distribution board.
- Type 2 SPD installed at sub-distribution boards.
  (Combined Type 1 and 2 SPDs are available and are usually installed in consumer units.)
- Type 3 SPD installed close to the protected load. These must only be installed as a supplement to a Type 2 SPD.

The History of Surge Protection Devices

Surge protection devices were developed in response to the growing need to protect electrical equipment from voltage spikes. These spikes can be caused by various factors, such as lightning strikes, power outages, or switching operations. The earliest forms of surge protection were basic and often ineffective. However, as technology advanced, so did the sophistication of SPDs.

Early SPDs consisted mainly of simple spark gaps, which provided minimal protection. The introduction of metal oxide varistors (MOVs) in the 1970s marked a significant advancement. MOVs could absorb larger surges, offering better protection for sensitive electronic equipment. Over the years, SPDs have evolved to include features like thermal disconnects and advanced monitoring capabilities, making them more reliable and efficient.

How Does a Surge Protective Device Work?

An SPD operates by diverting or limiting surge current to the ground and clamping the remaining voltage to a level that is safe for the connected devices. It usually consists of components like Metal Oxide Varistors (MOVs), gas discharge tubes, and transient voltage suppression diodes that react to voltage spikes and shunt the surge to the ground or neutral connection.

Key Components:

1. Metal Oxide Varistor (MOV): A non-linear resistor that changes resistance with the applied voltage. It conducts high-voltage surges away from sensitive equipment.

2. Gas Discharge Tubes (GDT): Used to protect against high transient surges by ionizing gas within a sealed container, allowing the surge to pass through.

3. Transient Voltage Suppression (TVS) diodes: Provide a means to clamp or limit the voltage and dissipate the surge energy.

What are transient overvoltages?

Transient overvoltages can be defined as short duration, high magnitude voltage peaks with fast rising edges, commonly referred to as ‘surges’, which can range from a few volts to many thousands of volts on a low-voltage consumer network, for no more than millisecond duration.

These surges occur due to the sudden release of energy previously stored or induced by other means. This energy can then find its way into electrical installations, naturally occurring either indirectly from lightning strokes or directly from lightning strikes, or created by the switching and operation of certain equipment within an installation.

How do transient overvoltages occur?

Transient overvoltages due to atmospheric origin can occur if either the property itself or nearby electrical transmission infrastructure suffers a hit by lightning strokes. These types of transient overvoltages are most likely to happen when a direct lightning stroke on an adjacent overhead power or telephone line causes the transient overvoltage to conduct along the lines into nearby properties, which can cause considerable damage to the electrical installation and associated equipment.

Common Causes:

1. Lightning Strikes: Direct or nearby strikes can induce high voltages.

2. Switching Operations: Sudden changes in the electrical load, such as turning on or off heavy-duty equipment.

3. Electrical Faults: Short circuits or faults within the power distribution system.

4. Electrostatic Discharge (ESD): Discharges from human contact or other electrostatic sources.

External Factors:

— Lightning: The most severe surges are caused by lightning, which can introduce thousands of volts into electrical systems.

— Grid Switching: Changes in the power distribution network, such as load shedding or fault clearing, can induce transient surges.

Internal Factors:

— Motor Start/Stop Cycles: Inductive loads like motors and transformers can cause switching surges.

— Fault Conditions: Arcing and fault clearing within the system can generate transient overvoltages.

Advancements in SPD Technology

Modern SPDs are highly effective, incorporating advanced technologies to enhance their performance. These devices now offer multi-stage protection, combining various components to provide comprehensive coverage against surges. The integration of thermal protection ensures that SPDs can disconnect safely when they overheat, preventing further damage.

Moreover, the development of Type 1, Type 2, and Type 3 SPDs has revolutionized the way electrical systems are protected. Type 1 SPDs are designed to handle direct lightning strikes, making them ideal for industrial and commercial installations. Type 2 SPDs protect against residual surges from indirect strikes and switching operations, while Type 3 SPDs offer local protection for sensitive equipment.

Main Types of SPDs

Surge Protective Devices (SPDs) are categorized into different types based on their installation points and the level of protection they offer. Understanding these types helps in selecting the appropriate SPD for your specific needs. The main types of SPDs are Type 1, Type 2, and Type 3.

1. Type 1 SPD

Type 1 SPDs are designed to protect against high-energy surges, primarily caused by direct lightning strikes or high-voltage events. They are typically installed before the main distribution board, either at the service entrance or integrated into the primary breaker panel. These devices can handle the brunt of the surge, channelling the excess energy safely to the ground.

— Industrial: Vital for factories and large-scale operations where the risk of lightning-induced surges is significant.

— Commercial: Implemented in commercial buildings, especially those with external lightning protection systems (LPS).

— Residential: Necessary for homes in areas with frequent lightning activity or those having external antennas or other metal structures.

Benefits:

– Offers the highest level of surge protection directly connected to the incoming power supply.

– Significant energy absorption capacity.

– First line of defense against large surges.

Example Applications:

– Electrical service entrances

– Main distribution boards in commercial complexes

– Buildings with external lightning protection systems

2. Type 2 SPD

Type 2 SPDs are designed to protect against residual surges that have passed through Type 1 SPDs or those indirectly coupled surges. They are installed at the main distribution panel or sub-panels within the building. Type 2 SPDs are essential for safeguarding against surges originating from switching operations and ensuring continuous protection across the electrical system.

— Residential: Commonly installed in homes to provide a secondary layer of defense after Type 1 SPDs.

— Commercial: Used in office buildings, retail establishments, and other commercial settings to protect against internal surges.

— Industrial: Installed in electrical sub-panels within manufacturing plants and other industrial setups to provide localized protection.

Benefits:

– Provides robust protection against residual surges.

– Enhances the efficiency of the overall surge protection system by addressing internally generated surges.

– Prevents damage to sensitive equipment connected to distribution panels.

Example Applications:

– Main and sub-distribution panels in residential properties

– Commercial building electrical systems

– Industrial machinery and equipment panels

3. Type 3 SPD

Type 3 SPDs are designed to protect against low-energy surges and are installed close to sensitive electronic equipment. These devices provide localized protection and are typically used to protect appliances, electronic devices, and other end-user equipment. Type 3 SPDs are the last line of defense in the surge protection hierarchy.

— Residential: Protects household appliances, entertainment systems, computers, and other sensitive electronics.

— Commercial: Used for office equipment, point-of-sale systems, and other critical electronic devices.

— Industrial: Provides protection for control systems, sensors, and other sensitive industrial electronics.

Benefits:

– Offers fine-grained protection for sensitive electronic devices.

– Protects against surges that may pass through type 1 and type 2 SPDs.

– Ensures the durability and reliability of end-user equipment.

Example Applications:

– Plug-in surge protectors for home electronics

– Office equipment surge protectors

– Dedicated surge protectors for industrial control systems

Should I Install an SPD?

Benefits of Installing SPD:

1. Protection: Safeguards sensitive electronic equipment from damage.

2. Longevity: Extends the life of electrical systems and appliances by mitigating surge-related wear and tear.

3. Safety: Reduces the risk of fire caused by electrical surges.

4. Cost Savings: Lowers maintenance and replacement costs due to surge-related damage.

Factors to Consider:

1. Environment: Areas prone to lightning or heavy electrical equipment should prioritize SPDs.

2. Equipment Sensitivity: Devices with high sensitivity to voltage fluctuations, like computers, telecom equipment, and medical devices, benefit significantly from SPDs.

3. Compliance: Ensure the SPD meets local electrical codes and industry standards.

Expert Recommendations:

Consult with a licensed electrician to assess your specific needs and recommend the appropriate type and rating of SPD for your installation. Regular maintenance and periodic testing of installed SPDs are also essential to ensure optimal performance.

Installation and Maintenance of SPDs

Proper installation and maintenance of SPDs are crucial for ensuring their effectiveness. SPDs should be installed by qualified professionals, following the manufacturer’s guidelines and the requirements of the 18th edition wiring regulations. Regular inspections and maintenance are also essential to ensure that SPDs are functioning correctly and providing the necessary protection.

During installation, it is important to ensure that SPDs are connected in parallel with the electrical system, allowing them to divert excess voltage to the ground. This setup ensures that SPDs can protect the entire system without interfering with normal operations. Additionally, SPDs should be installed as close to the protected equipment as possible, minimizing the distance that surge energy must travel.

Regular maintenance of SPDs involves checking for signs of damage or wear, ensuring that all connections are secure, and replacing any devices that have been compromised by previous surges. Many modern SPDs include status indicators that provide real-time information about the device’s condition, making it easier to identify when maintenance is needed.

Surge Protective Devices play a vital role in protecting electrical and electronic equipment from transient overvoltage. By understanding their working principles, types, and benefits, you can make informed decisions about safeguarding your electrical systems. Proper installation and maintenance of SPDs can lead to enhanced safety, reliability, and longevity of your equipment, making them an indispensable component of modern electrical installations.

Remember, the investment in SPDs can save significant costs and stress by preventing damage from unexpected voltage surges. Whether for residential, commercial, or industrial applications, ensuring your system is protected with the right SPD is a wise and necessary choice.