The voltage surges are elevations in voltage that can occur in electrical distribution, data communications and telephony lines resulting in a premature aging of components and / or damage to the equipment connected to the network.

Overvoltages caused by direct lightning, indirect, disconnection of inductive loads (coils, motors, etc ...), network switches and / or defects in them.

Overvoltage surges are large spikes have with a slope and are short-lived, yet the strong effects on sensitive electronic equipment are devastating.

The level of the voltage that can appear on the network is a function of isoceraúnico area level (lightning / year • Km2), the type of attack, aerial or underground, and the proximity of the MV / LV transformer.

For proper protection of the equipment against power surges, a system must perform grounding of low ohmic value and connect equipotentialy with an external protection system. Moreover, you should install protection against surges on supply lines (power, telephone, data, etc.).

Installation of external lightning protection (according to IEC 62305-3) and surge arresters (according to IEC 62305-4) significantly reduces the risk of damage caused by lightning in structures, equipment and people (calculation risks according to IEC 62305-2).

surge categories

The categories indicate what the value of voltage shock wave to withstand for the equipment and determine the maximum value of residual voltage Up which should have surge protectors in each area.

The purpose of installing surge protectors is to avoid the devastating effects of surges on electrical and / or electronic equipment, cutting these peaks to permissible values as per RBT ITC-23, depending on the category that has the equipment want to be protected

selection of surge protectors

Surge protectors are connected between an active conductor (phase) and ground, upstream of the equipment they protect.

Normal impedance is high, but when the voltage exceeds the threshold voltage, the protector becomes a low-impedance ground to dissipate the surge, protecting the equipment.

To select which protector to install, we must consider:

  • Nominal line voltage.
  • Number of phases to be protected.
  • Type of network (TT, TN, TNC, SCNT).
  • Category of equipment to be protected.
  • Level of exposure to surges (Imax).


Surge protection devices must conform to the following standards:

  • UNE EN 61643-11:2013 Low voltage surge protection devices.
  • IEC 62305 series – Lightning protection:
    • IEC 62305-1: Protection against lightning - General principles.
    • IEC 62305-2: Protection against lightning –Risk management.
    • IEC 62305-3: Protection against lightning – Physical damage to structure and life hazard.
    • IEC 62305-4: Protection against lightning – Electrical and electronic systems within structures.
  • UNE 21186:2011 /NF C 17-102:2011 Protection against lightning: Lightning rods with early stream emitters.
  • UNE EN 60664-1 Isolation coordination for low voltage equipment systems (networks).