Surge Protective Devices (SPD) are designed to protect electrical installations from transient overvoltages caused by lightning strikes or switching operations in the power network. By diverting surge currents safely to earth, SPDs reduce the voltage to a level that electrical equipment can safely withstand.

According to international standards, three main types of SPDs are used in low-voltage electrical systems: Type 1, Type 2, and Type 3.
The appropriate type depends on the installation environment, system configuration, and the level of protection required.

• Type 1 SPD

Type 1 surge protective devices are typically installed at the main electrical distribution board of buildings equipped with lightning protection systems. They are designed to discharge large lightning currents entering from the power supply and prevent them from damaging the electrical installation. Type 1 SPDs are generally used together with Type 2 devices to provide complete protection.

• Type 2 SPD

Type 2 SPDs are installed in sub-distribution panels to protect electrical circuits from residual lightning surges and switching overvoltages. They provide effective surge protection for most electrical installations and are widely used in residential, commercial, and industrial systems.

• Type 3 SPD

Type 3 SPDs provide fine protection for sensitive equipment such as electronic devices, communication systems, and control equipment. They are usually installed close to the protected equipment and are used in combination with upstream Type 2 SPDs to ensure optimal protection.