Transient and permanent overvoltage protection in small businesses

Small tertiary businesses, like any other sector of economic activity, are increasingly dependent on highly complex equipment, with electrical and electronic components that are very sensitive to transient and permanent surges. Surge protection of installations and equipment is not always performed properly, which has an impact on the safety of people and goods, and entails economic damage that is difficult to assume for a business of these characteristics.

Overvoltages are voltage spikes in the electrical network, measured between two conductors. Depending on their duration, they are classified as transient overvoltages (which are very short, in the order of microseconds) or permanent overvoltages (which last for several cycles).

Transient and permanent surges are very damaging to small tertiary businesses. On the one hand, they can lead to the disruption of connected systems, causing interruption of service and operations, as well as possible data loss and corruption, and other computer failures. Furthermore, they can cause overheating and damage to equipment components (circuit boards and other elements), which could destroy equipment and electrical installations and even cause fires. In other cases, degradation of electronic and electrical components develops unnoticed by the user, but leads to a decrease in the lifetime of the equipment and increases the likelihood of failure.

All of this translates into economic losses, both directly through having to replace damaged elements and indirectly through the interruption of processes. More importantly, overvoltages can also result in risks to people on the site.

For all these reasons, adequate surge protection is required to ensure the proper functioning of equipment and services both in normal circumstances and in situations that generate overvoltages.

We will now explain transient and permanent overvoltages in more detail, with emphasis on the solutions developed by Aplicaciones Tecnológicas S.A. for effective protection of small tertiary businesses.

Transient overvoltages: their causes and the functioning of protective devices

Transient overvoltages can have different origins including lightning, machinery switching processes, occasional voltage surges and electrical harmonics. The most common transient overvoltages are those caused by switching of high-power machinery or from switching and/or faults in the electrical system, while the most destructive are those generated by electrical storms.

Safety regulations require conventional electrical protection to operate for currents above 30 mA to avoid the risk of electrocution. In comparison, lightning current is typically tens of thousands of amperes (a million times greater)1 and can cause death, fire and destruction of equipment.

Although most of the electrical system has safety measures (circuit breakers, MCBs and RCDs) to prevent short circuits and electric shocks to people, their slow activation does not safeguard against transient overvoltages.

Surge protection devices (SPD) are complementary to this conventional protection. Their aim is to maintain continuity of service and to reduce the likelihood of incidents caused by transient overvoltages to a level acceptable for the safety of persons and property.

SPDs are inactive with small signal distortions and mains overloads, but when a transient overvoltage spike occurs they respond immediately (around 20-100 nanoseconds), conducting the current to earth and protecting the connected equipment. After absorbing the surge they return to their inactive state and no longer affect signal operation.

Surge protectors must not only be able to withstand all the current that reaches them, but they must also leave a voltage on the line that is bearable for the equipment connected to it. It is therefore important to know the specifications of the equipment connected to them.

SPDs are selected according to the risk calculation (surge risk of the site and the risk of the connected equipment). Usually several coordinated protectors are used, arranged in several sequential stages to meet the requirements of withstanding the current and leaving residual voltages not harmful to the equipment.

The installation of protectors against overvoltages is desirable on all lines entering and leaving the building, as well as on all lines connected to sensitive equipment, whether power supply, telecommunications or data lines.

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Causes of permanent overvoltages and performance of surge protectors

Permanent overvoltages are voltage increases of more than 20% of the nominal value of the distribution network, maintained for several cycles or permanently. They are caused by phase decompensation due to neutral breakage, faults in the neutral conductor connection, consumption drops or faults in the transformer substations.

Permanent overvoltage protectors disconnect the power system from the grid that is subject to the surge. This disconnection can be carried out by acting on a circuit breaker or differential switch, or on a device with automatic reclosing. In the first case, the protector must include an emission coil, and the reset or reconnection is carried out manually. In the second case, the device can be a contactor, so that the resetting is automatic. This second option is especially recommended for unattended areas.

Aplicaciones Tecnológicas S.A. solutions for overvoltages

Surge protection in the commercial environment is similar to residential protection, but must be adapted to the needs of each business and the characteristics of the facility.

Small businesses in the tertiary sector (e.g. shops, workshops, restaurants, etc.) generally do not have much space for the installation of surge arresters. Therefore, the most suitable solution is the use of combined systems, which integrate protection against transient and permanent surges in the same device. From Aplicaciones Tecnológicas S.A. we recommend the ATCONTROL/R COMPACT series, type 2 surge protector for single-phase connections, KIT ATCONTROL/R, type 2 surge protector for three-phase lines, and ATPLUG CONTROL, type 3 plug-in single-phase surge protector.

The ATCONTROL/R COMPACT series of Aplicaciones Tecnológicas S.A. acts when it detects permanent overvoltages or undervoltages by triggering an internal relay; and automatically reconnects to the grid circuit when these cease. In addition, if it detects a transient overvoltage, it diverts the current to earth and reduces the voltage to a level that is not harmful to the connected equipment.

For three-phase lines, the KIT ATCONTROL/R series cuts the line when it detects a permanent overvoltage or undervoltage, protecting the installed equipment. Like ATCONTROL/R COMPACT, it is also an automatic resettable protector, so that when the permanent overvoltage ceases, the protector reconnects the contactor. It also acts against transient overvoltages.

For sophisticated protection of the most sensitive equipment, the ATPLUG CONTROL series are pluggable, automatically reclosing surge protectors that protect against permanent overvoltage, transient overvoltage and undervoltage. In the event of permanent overvoltage or undervoltage, they disconnect the power supply from the socket. After the overvoltage has ceased, the protector reconnects the power supply to the load. Like ATCONTROL/R COMPACT and KIT ATCONTROL/R, ATPLUG CONTROL surge protectors also protect against transient overvoltages.

Protection against transient and permanent overvoltages is vital to avoid security risks, failures and destruction of equipment, as well as the reduction of their useful life. Aplicaciones Tecnológicas S.A. has the best solutions, tried and tested in official and independent laboratories according to the applicable regulations, to protect small businesses in the tertiary sector.

If you would like more information on which surge protectors to use and where to place them in your business, you can contact us at the following link.


  1. Instituto Nacional de Seguridad e Higiene en el Trabajo. NTP 1084 Prevención De Riesgos Laborales Originados Por La Caída De Rayos. Notas técnicas de prevención (2017).