Created by: Glen Zhu | Updated Date: March 17th, 2025
Type 3 surge protector is an electrical device used to protect terminal equipment from transient overvoltage (surges) damage. It is commonly referred to as a Point-of-Use SPD because it is directly installed near the equipment, such as sockets, power boards, or power adapters. Type 3 SPDs are mainly used to resist low-energy surges caused by internal disturbances in the power system (such as switch operations, inductive load start-ups) and external disturbances (such as lightning strikes or grid fluctuations).
The main function of Type 3 SPD is to absorb or divert momentary high voltage surges to protect terminal electronic equipment from damage. Specifically, its functions include:
The necessity of surge protection to power distribution boards can never be overstated. Among all protective measures, surge protection devices (SPDs) is an important aspect and is wildly applied in todays’ electric systems.
Modern household appliances and electronic products (such as TVs, computers, smart home devices) are very sensitive, even tiny power surges can cause component damage or shorten lifespan. Type 3 SPD can effectively suppress surge voltage to prevent circuit boards and chips from being impacted.
2. Supplement Type 1 and Type 2 SPD for multi-level protection
In a complete surge protection system, Type 1 SPD is installed at the building’s power entrance to defend against external lightning strikes; Type 2 SPD is installed in the distribution panel to prevent grid surges from entering branch lines.
Type 3 SPD serves as the final line of defense, protecting equipment from residual surges’ effects, ensuring that even if the first two levels of SPD cannot completely eliminate surges, terminal equipment remains safe.
Frequent power surges may lead to instability in electronic devices such as computer data loss, household appliance malfunctions or damage. Type 3 SPD reduces electrical stress by suppressing voltage spikes, making equipment operate more stably.
Excessive surges may cause overheating of equipment, insulation damage or even fires. Type 3 SPD effectively diverts overvoltage to reduce the risk of electrical fires occurring and enhance overall safety.
The main working principle of Type 3 surge protector is to quickly reduce overvoltage when voltage surges are detected, diverting excess energy to ground in order to protect terminal equipment. It typically consists of metal oxide varistors (MOV), gas discharge tubes (GDT), or transient voltage suppression diodes (TVS), which conduct when surge voltages exceed safe thresholds, limiting the voltage within the range that the equipment can withstand.
When the circuit is at normal operating voltage, Type 3 SPD is in a high impedance state and does not affect current flow; however, when surges occur, the SPD instantly switches to a low impedance state, quickly diverting excess energy, and then returns to a high impedance state to ensure the normal operation of the power system.
Type 3 surge protective devices (SPDs) are mainly used for the protection of terminal equipment, capable of absorbing residual surges to ensure the safe operation of electronic devices. Due to their small size and flexible installation, Type 3 SPDs are suitable for a variety of fields including residential, commercial, industrial, and medical. The following are the main application scenarios for Type 3 SPDs:
In modern households, more and more electronic devices are sensitive to voltage fluctuations, such as smart home appliances, entertainment devices, and personal computers. Type 3 SPD protects terminal equipment from damage and performance degradation caused by power surges.
Applicable devices:
TVs and home theater systems – protect LCD TVs and audio systems from lightning strikes or power grid fluctuations.
Smart home devices – such as smart sockets, smart lighting, smart door locks, etc., protect their microelectronic components from surge damage.
Computers and network equipment – protect desktops, laptops, routers, NAS storage devices to prevent data loss or hardware damage.
Kitchen appliances – microwaves, refrigerators, coffee makers etc., these devices have electronic control boards inside that are easily affected by surges.
Installation method: Type 3 SPD is usually integrated into sockets or power extension cords to ensure plug-and-play convenience for protecting household appliances.
In the corporate and commercial environment, Type 3 SPD can protect key office equipment, preventing data loss, equipment damage, or business interruption caused by surges.
Applicable Equipment:
Servers and data storage devices – Protect server rooms, UPS equipment, and storage systems to avoid crashes or data damage caused by power surges.
Office electronic equipment – Copiers, printers, POS machines etc., ensuring long-term stable operation of the devices.
Monitoring and security systems – Protect CCTV surveillance cameras, access control systems from lightning strikes or unstable power grids causing device damage.
Commercial lighting systems – LED lighting, smart lighting control systems etc., avoiding surge-induced lamp damage or accelerated light decay.
Installation method: Type 3 SPD can be directly installed in rack power distribution units (PDUs), independent sockets or power filters to ensure the safety of office equipment.
In industrial environments, devices such as PLCs (Programmable Logic Controllers), variable frequency drives, sensors are often exposed to complex electrical environments and are susceptible to surge impacts. Type 3 SPD can effectively protect these devices, ensuring stable operation of production systems.
Applicable Devices:
PLC control systems – Prevent surge interference in industrial automation control systems, improve production stability.
Variable frequency drives and motor drives – Avoid control failures or equipment damage caused by surges, reduce maintenance costs.
Sensors and measuring instruments – Protect precision measuring instruments, ensure data accuracy and long-term reliability of equipment.
Industrial displays and Human Machine Interfaces (HMI) – Avoid touch screen malfunctions or communication abnormalities caused by surges.
Installation method: Type 3 SPD can be installed at device ports or independent power supply units to reduce the risk of terminal equipment damage.
Electronic devices in medical environments require high power quality. Voltage fluctuations or transient surges may affect the accuracy of medical equipment and even endanger patient safety. Type 3 SPD can effectively protect precision instruments and ensure the normal operation of medical systems.
Applicable equipment:
CT, MRI, and ultrasound equipment – Avoid damage from surges to ensure diagnostic accuracy.
Life monitoring equipment – Protect ECG machines, blood pressure monitors, etc., to prevent data loss or false alarms due to surges.
Laboratory instruments – Ensure the long-term stable operation of biochemical analyzers, electron microscopes, and other equipment.
Operating room equipment – Prevent surges from affecting the normal operation of key equipment such as surgical lights, anesthesia machines, and electric operating tables.
Installation method: Type 3 SPD can be built into the power module of medical devices or connected to external power stabilizers to improve device stability.
Modern buildings widely adopt intelligent control systems, such as Building Management Systems (BMS) and Internet of Things (IoT) sensor devices. Type 3 SPD ensures the stability of these systems, preventing signal loss or equipment damage caused by surges.
Applicable devices:
Intelligent lighting control system – Ensures that building intelligent lighting systems can operate normally even in stormy weather.
Building Management System (BMS) – Protects elevator controls, air conditioning systems, security monitoring, etc., ensuring the stability of building automation systems.
Internet of Things (IoT) devices – Protects smart sensors, wireless controllers, data gateways, etc., preventing communication failures or data loss caused by power surges.
Installation method: Type 3 SPD is typically installed at the power interface of the device or in Power over Ethernet (PoE) equipment to ensure data and power safety.
Type 3 SPD is mainly used for terminal equipment protection, so different application scenarios require selecting the appropriate model.
Type 3 SPDs need to match the voltage level of the operating environment to ensure compatibility and protection effectiveness.
| Application equipment | Nominal voltage（Un） | Recommended SPD rated voltage |
| Home electronic devices | 120V / 230V | 150V / 255V SPD |
| Business office equipment | 120V / 230V | 150V / 255V SPD |
| Industrial control equipment | 24V / 48V / 60V DC | 30V / 60V / 75V SPD |
Make sure that the rated voltage of the SPD is equal to or higher than the operating voltage of the equipment to avoid misoperation or protection failure.
Type 3 Surge Protector TLP-150
Uc (Maximum Continuous Operating Voltage) is the maximum voltage that an SPD can withstand for a long period of time.
Up (Voltage Protection Level) is the limiting voltage of SPD when surges occur, the lower the value, the better protection for equipment.
Different Type 3 SPDs use different connection methods, affecting their applicability.
SPD types | Installation method | Applicable devices |
Socket type SPD | Directly plug into the socket | Household appliances, office equipment |
DIN rail type SPD | Installation inside the distribution box | Industrial equipment, smart buildings |
Power cord with built-in SPD | Built-in PDU, UPS | Server, medical equipment |
PoE network SPD | Protect network interface | Surveillance equipment, IoT devices |
High-quality Type 3 SPD must comply with international safety standards, such as:
There is a significant price difference for Type 3 SPDs on the market, but cheap SPDs may use
1. Install Type 3 Surge Protector
A. Pre-installation preparation
1. Disconnect power: Before starting any installation work, be sure to turn off the relevant power supply. Ensure that the power is completely turned off to avoid electric shock hazards.
2. Check equipment and tools: Make sure you have the appropriate tools, such as a multimeter, cable stripping pliers, insulated screwdriver, grounding wire, etc., to ensure safety and installation quality.
B. Installation steps
1. Socket-type SPD installation (for home and office equipment)
2. DIN rail-mounted SPD installation (for distribution boxes, industrial equipment)
3. PoE / data line SPD installation (for network devices)
A. Regular Inspection and Maintenance
To ensure that Type 3 SPD continues to effectively protect equipment, it is necessary to regularly inspect its operational status.
1. Inspect every 6 months
2. Clean installation location
B. Test and Evaluate SPD Performance
A. When to replace
To ensure that the Type 3 SPD is working properly, you can test it using the following methods:
1. Check indicator lights: Most Type 3 SPDs come with indicator lights (such as green for normal, red for damaged), observe the status of the indicator lights to determine if the SPD is working properly.
2. Use a multimeter for testing: Use a multimeter to check if there is excessive residual voltage at the output terminal of the SPD, a normal Type 3 SPD will clamp surge voltages within a safe range.
3. Check grounding: Use a multimeter to check if the SPD is well connected, ground resistance should be less than 10Ω. Poor grounding system may cause the SPD to not work effectively.
Yes, Type 3 SPDs need to be checked regularly and replaced according to usage. You may need to replace the SPD if:
1. The indicator light is abnormal: When the indicator light turns red or completely goes out, it means the SPD has failed and needs to be replaced.
2. It has experienced multiple surge events: As the number of surges increases, the protective ability of the SPD will decrease, so it should be replaced promptly after prolonged exposure to excessive surges.
3. Equipment malfunctions: If connected devices are damaged and no other cause can be found, it may be due to a damaged SPD causing surge protection failure.
The lifespan of a Type 3 SPD usually depends on its frequency of use, the number of surges it experiences, and the load conditions of the electrical system. Generally, the lifespan of an SPD can reach 3-5 years, but if it frequently encounters lightning strikes or strong surge events, the lifespan may be shortened.
1. High-frequency surge events: If the device often experiences lightning strikes or voltage surges, the SPD will gradually fail.
2. Standard environmental use: In normal environments and without frequent exposure to high-intensity surges, an SPD’s lifespan can be maintained for 5 years or even longer.
LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!
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