6.11Determining need for power surge protection devices#
Surge protection devices are not required under AS/NZS 3000; however, designing with SPDs may come under the requirements of the Electrical Safety Act 2002 for the minimisation of risk. The need for SPDs will depend on the likelihood of surges occurring, the consequences if the equipment is damaged by a surge, and whether the equipment is already protected by an internal SPD. Consequently, a risk assessment should be carried out for particular installations. Assessment and management of risk due to lightning and an analysis of the need for protection is covered in AS/NZS 1768. The Excel™ spreadsheet Risk Assessment for Lightning Protection accompanying AS/NZS 1768 should be referred to as a guide to the need for surge protection.
Where any of the following conditions exist, consideration should be given to the risks involved to the electrical / electronic installation:
- high prevalence of lightning and thunderstorm activity
- location at end of extensive electrical overhead lines
- location in industrial areas where power disturbances are frequent
- exposed or isolated site
- expensive, critical and / or sensitive electronic equipment is within the installation, and
- surge generators located within the installation.
If protection is required, it should be installed at the entries to the installation. Where equipment likely to cause surge are installed within the installation, additional protection may be necessary close to critical equipment. When equipment to be protected is located close to the main switchboard, or when it has sufficient overvoltage withstand, one SPD at the switchboard may be sufficient. Where the voltage protection level (Up₁) (which is the maximum voltage expected across the terminals of the SPD) of the entry SPD is less than 80% of the withstand voltage (Uw) of the equipment to be protected, no additional protection is usually necessary close to the equipment. Additional protection close to the equipment may be necessary where:
- sensitive electronic equipment is present
- distance between the entrance SPD and equipment to be protected is greater than 10 m, and/or
- electromagnetic fields are generated within the structure.
If Up₁ is greater than 80% of the withstand voltage (Uw) of the equipment to be protected, additional protection may be necessary close to the equipment. The voltage protection level (Up₂) of this second SPD should be less than 80% of the equipment withstand voltage. In summary: Protection installed at the installation entry is generally sufficient if
𝑈𝑝1 < 0.8 𝑈𝑤#
Protection installed at the installation entry and addition protection is generally required if
For the additional protection
𝑈𝑝2 < 0.8 𝑈𝑤#
where Up₁= voltage protection level of the entry SPD Up₂ = voltage protection level of SPD adjacent to equipment to be protected Uw = equipment withstand voltage
Consideration should also be given to the attenuation of waveforms by the internal cabling of the structure.
