What's Differences Between Surge Protective Devices and Circuit Breakers
- Differences Between surge protective devices and Circuit Breakers
1.1 surge protective device
A surge protective device (SPD), also known as a low voltage lightning arrester or low voltage surge arrester, is a device used to limit surges caused by strong transient overvoltages in electrical circuits or communication lines, thereby protecting the equipment. Its working principle is that when a transient overvoltage or overcurrent occurs in the circuit, the surge protective device will quickly conduct, diverting the surge to the ground.
According to the type of equipment being protected, surge protective devices can be divided into two categories: power surge protective devices and signal surge protective devices. Power surge protective devices can be further classified, based on protection capacity, into Type 1, Type 2, Type 3, and Type 4 power surge protective devices. Signal surge protective devices include network signal surge protective devices, video surge protective devices, 3-in-1 surveillance surge protective devices, control signal surge protective devices, and RF (antenna-feeder) signal surge protective devices.
1.2 Circuit Breaker
A circuit breaker, sometimes called an air switch, is a safety device used in electrical systems. It disconnects the circuit automatically when the current goes beyond a set limit. This protects electrical circuits and equipment from issues like short circuits or overloads.
People often use circuit breakers to control power in places like lighting systems or pump rooms. The device works based on heat. When too much current flows through the breaker, it produces heat. This heat causes a metal strip inside the breaker to bend. As a result, the breaker trips and cuts off the power. This prevents damage to the equipment caused by excessive current.
- Differences Between the Two Devices
2.1 The working principles are different: A surge protective device conducts when a transient overvoltage occurs in the circuit, diverting the excess voltage to the ground. In contrast, a circuit breaker automatically disconnects the circuit when the current exceeds the rated limit, thereby protecting electrical equipment.
2.2 The protection functions are different: A surge protective device is designed to safeguard electrical and communication equipment from surge damage within the circuit. A circuit breaker, on the other hand, protects the circuit from faults such as short circuits and overloads.
The protection scopes are different: A surge protective device can protect both power supply systems and communication lines. A circuit breaker is limited to protecting electrical equipment connected to the power circuit.
- Basic Knowledge for Surge Protective Device (SPD) Selection
Key selection factors of surge protective device include the following:
The voltage protection level (Up) should be selected according to the withstand voltage of the protected equipment to ensure that the protection voltage is lower than the insulation withstand level, thus protecting the equipment from damage caused by overvoltage. The Up value should be less than 80% of the insulation withstand voltage of the protected equipment. For example, in the branch distribution box of a residential building, the Up value is usually selected between 1.5kV and 2.5kV. When protecting sensitive electronic equipment such as smart home control systems, a lower Up value should be selected.
The maximum continuous operating voltage (Uc) indicates the maximum AC RMS or DC voltage that the SPD can safely withstand over a long period. It should be greater than the maximum continuous operating voltage that may appear in the system and is generally selected based on the system’s nominal voltage. In a 220V/380V residential power supply system, a Uc value of 385V or 420V is typically selected. In a photovoltaic system, the Uc value of the surge protective device should be selected based on the maximum input voltage of the photovoltaic inverter. When the power supply system has large voltage fluctuations, a higher Uc value should be chosen.
The discharge capacity refers to the maximum surge current that the SPD can withstand in a single surge event. It includes the nominal discharge current (In) and the maximum discharge current (Imax). Selection should be based on the installation location and the potential intensity of lightning surges. For example, at the main distribution box, a larger discharge capacity is required, while at the terminal distribution box, a smaller capacity may suffice. The nominal discharge current (In) represents the level of surge current that the SPD can withstand repeatedly without damage. The selection of In depends on factors such as location, height, surrounding environment, and required lightning protection level. In urban areas with surrounding tall buildings, In may be selected as 20kA; in open areas or regions with frequent lightning activity, In should be 30kA or higher.
The maximum discharge current (Imax) represents the maximum surge current the SPD can withstand in a single event. The selection is similar to In but must also consider the installation environment, the importance of the building, and the value of the equipment. For ordinary residential buildings, Imax may be selected between 40kA and 60kA; for high-end residential buildings or sites with critical equipment, Imax should be 80kA or above.
The response time reflects the SPD’s speed in reacting to lightning surges. The shorter the response time, the better. Generally, it is recommended to choose SPDs with a response time of less than 25ns to ensure fast suppression and discharge of surges, minimizing potential damage to equipment.