Overvoltage means a voltage in an electrical system which is higher than tolerance range of its nominal voltage. Europe voltage is 230V (plus / minus 23 volts). Some electrical appliances requires 3 phases / 380 (400) Volts.
A lightning strike can cause high overvoltage, damaging some devices and electrical installations.
There are 3 types (classes) of overvoltage protection devices (Surge Protection Device).
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Type 1 SPD
Protects building electrical installations against direct lightning strokes. It can discharge the back-current from lightning spreading from the earth conductor to the network conductors.
Type 1 reduce the overvoltage level to 4 kV or lower. The Type 1 SPD (Surge Protection Device) is recommended in the specific case of service-sector and industrial buildings, protected by a lightning protection system or a meshed cage. Type 1 SPD is characterized by a 10/350 µs current wave.
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Type 2 SPD
The Type 2 SPD is the main protection system for electrical installations inside building. Installed in each electrical switchboard, it prevents the spread of overvoltages in the fixed electrical installations and protects the loads.
Type 2 reduces the overvoltage level at 2.5 kV or lower
Type 2 SPD is characterized by an 8/20 µs current wave.
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Type 3 SPD
SPD (Surge Protection Device) Type 3 have a low discharge capacity. They must be installed as a supplement to existing Type 2 SPD and in the vicinity of sensitive loads.
If the protected device is far from the previous stage overvoltage protection more than 10 m (by cable), protection is needed repeat. Overvoltage induced on a cable that is too long cannot eliminate previous Type 2 SPD, and thus the device is endangered. What the closer the Type 3 SPD is to the protected device, the better the overvoltage protection secured.
This gentle protection ensures that the overvoltage level does not exceed 1.5 kV. It responds to surges from all three stages the fastest. Type 3 SPD is characterized by a combination of voltage waves (1.2/50 μs) and current waves (8/20 μs).
In the context of NETIO products
It can various per device and type of the output, but generally NETIO devices contains Overvoltage protection SPD Type 3. Mostly 125J (8/20us).