The Surge protector device is an appliance or device intended to protect electrical devices from voltage spikes in alternating current (AC) circuits. It is important to protect the electrical safety for our equipment.

Three rules of thumb for choosing surge protection

1.    Familiarize yourself with types of SPDs.

2.    How to choose different function SPD

3.    Use the right devices to protect the surge protection itself.

Protection types of SPD

The first level of power protection:

According to the requirements of the national standard: a surge protector of Class I test should be installed at the main distribution box where the power supply is introduced. The voltage protection level of the surge protector should be less than or equal to 2.5 kV. When the impulse current value Iimp of each protection mode cannot be determined, the impulse current should be equal to or greater than 12.5 kA. Therefore, the first-level surge protector needs to choose products with T1 test (10/350μs test waveform) parameters, and the impulse current Iimp≥12.5kA.

The second level of power protection:

The second level selects products with T2 test (8/20μs test waveform) parameters, the maximum current capacity (Imax): 40~100kA, the nominal current capacity (In): 20~50kA.

The third level of power protection:

The third level is generally a single-phase power surge protector. The third level selects products with T2 test (8/20μs test waveform) parameters. The maximum current capacity (Imax) is 20kA, the nominal current capacity (In), and the maximum continuous Working voltage 275VAC, protection level Up: 1.2kV

How to choose different function SPD?

The working principle of voltage switch type surge protector

      When there is no instantaneous overvoltage, it appears as high impedance. Once it responds to lightning and alternating current instantaneous overvoltage, its impedance suddenly changes to a low value, allowing large currents to pass. Because of its large lightning discharge energy, it is usually installed at the entrance of a building. When used as such devices, the components generally include: discharge gap, gas discharge tube and thyristor, etc.

Working principle of voltage-limiting surge protector

         It is high impedance when there is no instantaneous overvoltage, but with the increase of surge current and voltage, its impedance will continue to decrease, and its current-voltage characteristics are strongly nonlinear. Although its lightning discharge energy is small, its overvoltage suppression capability is good, which is used to limit the excessive voltage generated in the subsequent stage after the lightning current of the previous stage is discharged. The devices used in such devices are: varistors, suppressor diodes, and avalanche diodes.

Risk assessment

Assessing risk is generally a complex, painstaking process. A good starting point is to think about what kinds of areas are most and least at risk. You can then consider the type of SPD best suited to the kind of building you’re planning to protect – if it has a single service entry switchboard.

One or two tips for risk assessment

Use European HD 60364-5-53, for example. Some countries make it compulsory to use this standard when considering surge protection for big and/or highly sensitive buildings like industrial facilities, hospitals, and data centers.

Otherwise, bear this rule of thumb in mind: always install a Type 2 surge protection. If the distance between the surge protector and the equipment to be protected is greater than 10 meters, then add a Type 2 or Type 3 SPD, close to the load to be protected.

Use the right devices to protect the surge protection itself

Usually 63A fuse is used in circuit to protect SPD of Type 2 or Type 1+Type2, but if the whole line use only Type 1 SPD, we need to revised control fuse to 125A in case of any risk in damage of surge protective device.

How to fix the SPD when it was damaged?

The SPD is combined with insert core (MOV) inside and socket. When the SPD is damaged, the indicator on the SPD will change the color from green to color, that means we need cut off the circuit to change a new insert core.