Classification of Surge Protective Devices (SPDs)

The manufacture shall classify the SPDs in accordance with the following parameters.

• One. One-port SPD is surge protective device having no intended series impedance. A one port SPD may have separate input and output connections.
• Two. Two-port SPD is surge protective device having a specific series impedance connected between separate input and output connections.

• Voltage switching. Voltage switching type SPD is SPD that has a high impedance when no surge is present, but can have a sudden change in impedance to a low value in response to a voltage surge. Common examples of components used in voltage switching type SPDs are spark gaps, gas tubes and thyristors. These are sometimes called “crowbar type” components.
• Voltage limiting. Voltage limiting type SPD is SPD that has a high impedance when no surge is present, but will reduce it continuously with increased surge current and voltage. Common examples of components used in voltage limiting type SPDs are varistors and avalanche breakdown diodes. These are sometimes called “clamping type” components.
• Combination. Combination type SPD is surge protective device that incorporates both, voltage switching components and voltage limiting components. The surge protector may exhibit voltage switching, limiting or both.

Information required for class I, class II and class III tests is given in Table 1.

Table 1 – Class I, II and III tests

Notes:

Class I tests are tests carried out with the impulse discharge current I_imp, with an 8/20 current impulse with a crest value equal to the crest value of I_imp, and with a 1,2/50 voltage impulse.

Class II tests are tests carried out with the nominal discharge current I_n, and the 1,2/50 voltage impulse.

Class III tests are tests carried out with the 1,2/50 voltage – 8/20 current combination wave generator.

• Indoor. SPDs intended for use in enclosures and/or inside buildings or shelters. SPDs installed in outdoor enclosures or shelters are considered for indoor use.
• Outdoor. SPDs intended for use without enclosures and outside of buildings or shelters (e.g. on low-voltage overhead lines).

By definition, outdoor means outside closed shelters. Hence, such SPDs are subjected to all external conditions. Indoor means inside closed shelters. Hence, such SPDs are subjected to indoor atmospheric conditions.

• Accessible. An surge protective device which can be fully or partly touched by an unskilled person, without the use of a tool to open any covers or enclosures, once installed.
• Inaccessible (out-of-reach). An surge protective device which cannot be touched by an unskilled person either due to being mounted out of reach (e.g. mounted on overhead lines) or due to being located within enclosures which can only be opened by using a tool, once installed.

Out-of-reach means no access to live parts without the use of tools or other equipment.

• Internal;
• External;
• Both (internal and external).

• Thermal;
• Leakage current;
• Overcurrent;

According to IP code of IEC 60529.

• Normal. Normal range: –5 °C to +40 °C. This range addresses surge protective devices for indoor use in weather-protected locations having neither temperature nor humidity control and corresponds to the characteristics of external influences code AB4 in IEC 60364-5-51.
• Extended. Extended range: –40 °C to +70 °C. This range addresses surge protective devices for outdoor use in non weather protected locations.

• Normal. Normal range: 5 % to 95 %. This range addresses SPDs for indoor use in weather-protected locations having neither temperature nor humidity control and corresponds to the characteristics of external influences code AB4 in IEC 60364-5-51.
• Extended. Extended range: 5 % to 100 %. This range addresses SPDs for outdoor use in non weather protected locations.

• AC between 47 Hz and 63 Hz;
• AC other than the range of 47 Hz to 63 Hz;

This may require additional and/or modified test procedures.

Multipole SPD is a type of surge protective device with more than one mode of protection, or a combination of electrically interconnected SPDs offered as a unit.

• open circuit (standard type SPD);
• short-circuit (short-circuiting type SPD).