Surge Protection Units
Surge Protection Devices (SPDs) are essential components designed to safeguard electrical systems and equipment from surge events. These devices play a crucial role in limiting transient voltages and diverting surge currents, protecting against both external sources like lightning and internal sources such as the switching of electrical loads.
Without proper surge protection, transient events can cause harm to electronic equipment and result in costly downtime. To understand the importance of surge protection devices, it's essential to delve into how they work and the key factors that contribute to their performance.
How Does an SPD Work?
At its core, an SPD limits transient voltages and diverts the current back to its source or ground when a transient voltage occurs on the protected circuit. This process involves the use of non-linear components that transition between high and low impedance states.
Under normal operating conditions, SPDs remain in a high-impedance state and do not affect the system. However, when a transient voltage occurs, the SPD switches to a low-impedance state, diverting the surge current and clamping the voltage to a safer level. After the transient is diverted, the SPD automatically resets back to its high-impedance state.
SPD Categories or Types
There are two main types of SPDs: voltage limiting and voltage switching components. Voltage limiting components, such as metal oxide varistors (MOVs) and transient voltage suppression (TVS) diodes, change in impedance as voltages rise, effectively clamping the transient voltage. On the other hand, voltage switching components, like gas discharge tubes (GDTs) and spark gaps, "turn on" once a threshold voltage is exceeded and quickly drop to a low impedance state.
Most modern systems incorporate a combination of both voltage limiting and voltage switching components to maximise protection. This hybrid approach allows the strengths of each component type to be leveraged while minimising their weaknesses.
Comparing SPD Categories
When comparing surge protection components, several factors come into play:
Response Time: This refers to how quickly a component reacts when the surge threshold is surpassed. Voltage limiting components like TVS diodes have faster response times compared to voltage switching components like spark gaps and GDTs.
Follow-On Current: This phenomenon is specific to voltage switching devices. Follow-on current occurs when an SPD fails to return to a high-impedance state following a transient event, allowing current to continue flowing during normal operation. While less of a concern in AC systems, it requires consideration in DC systems using voltage-switching devices.
Let-Through Voltage: Let-through voltage is the amount of voltage that a component allows to reach the connected equipment during a surge. Diodes excel in limiting voltage and keeping it low, but their effectiveness diminishes when handling larger surge currents. MOVs, on the other hand, are considered serviceable in all categories but not the best in any single one.
It's important to note that most SPD products on the market today are hybrid designs that combine multiple surge components. These products offer balanced protection against various types of surges by leveraging the strengths of each individual component.
Surge Protective Device Performance Features
When selecting an SPD, it's essential to consider its performance features. Key aspects to evaluate include:
Maximum Continuous Operating Voltage (MCOV): The MCOV represents the maximum voltage that the device can withstand while continuing to operate effectively. Typically, the MCOV should be at least 25% above the nominal supply voltage, although specific standards may dictate different requirements.
Voltage Protection Rating (VPR) or Voltage Protection Level (Up): These ratings relate to the let-through voltage of the device and are defined by UL and IEC standards. They measure the voltage allowed to pass through the device when subjected to a specific test waveform.
Nominal Discharge Current (In) Rating: This rating indicates the peak value of current that the SPD can conduct while still functioning after a specific number of applied surges. Manufacturers select a nominal discharge current from a predefined list for this test.
Indication Status: An indication status feature, such as a mechanical indicator, LED, or remote alarm, provides a simple Go/No-Go indicator, allowing users to easily determine if the SPD is operational.
While surge rating is often considered a crucial factor, it's important to note that surge current capacity or maximum surge ratings are not defined by UL or IEEE standards. Each manufacturer may have their own testing requirements, making these ratings less reliable indicators of performance.
SPD Classes or Types
SPDs are categorised by type (UL) or test class (IEC) according to relevant standards. These classifications help determine the appropriate SPD for specific applications. The three main types are:
Type 1 SPDs: These devices are designed to discharge partial lightning currents and are typically installed at the origin of the electrical installation. Type 1 SPDs are often used in conjunction with Type 2 devices to provide comprehensive protection.
Type 2 SPDs: Type 2 SPDs prevent the spread of overvoltage within electrical installations and protect connected equipment. They are commonly installed in sub-distribution boards and can be used as the primary device when Type 1 protection is not required.
Type 3 SPDs: Type 3 SPDs have a lower discharge capacity and are used as supplementary protection alongside Type 2 SPDs. They are typically installed in close proximity to sensitive loads.
Understanding the terminologies associated with SPDs can further aid in selecting the appropriate device:
Iimp: Impulse current associated with Type 1 SPDs.
In: Surge current associated with Type 2 SPDs.
Up: Residual voltage measured across the terminal of the SPD when In is applied.
Uc: Maximum voltage that can be continuously applied to the SPD without it conducting.
Surge Protection Consumer Units
To attain the most formiddable level of circuit protection look no further than the highly rated FuseBox range. Fitted with a T2 SPD and mains switch, they offer unparalleled protection and all at a very reasonable price. FuseBox surge protection consumer units use RCBOs as their outgoing devices which provides individual overload and residual protection for each circuit.
Maintenance and FAQs
Most SPDs feature indication windows that display their operational status. Green indicates proper protection, while red signifies the end of the device's service life, indicating the need for replacement. Some SPDs have replaceable cartridges, making the replacement process simple and efficient.
Here are answers to common questions about surge protection:
What does surge protection do?
Surge protection devices safeguard electrical equipment from voltage spikes and surges, preventing damage and ensuring the longevity of the connected devices.
Are surge protection devices necessary?
Yes, surge protection devices are essential, especially in environments where surges can lead to serious consequences like injury, data loss, or financial loss. The 18th edition wiring regulations mandate surge protection in such cases.
What types of facilities require surge protection devices?
Facilities housing critical equipment like medical devices, data centres, industrial control systems, and commercial establishments should have surge protection devices in place to ensure uninterrupted operations and prevent damage.
By implementing surge protection devices in accordance with regulations and selecting the right SPDs for specific applications, organisations can safeguard their electrical systems, protect valuable equipment, and ensure business continuity.