Variation in mains voltage, why does it occur?

The electrical networks are susceptible to several problems that can damage the equipment of the installations, such as the drops and variations in voltage, which occur frequently. In this article, we will address why these voltage fluctuations, how voltage variation can be corrected, which voltage variation value is acceptable, how to proceed in these cases, and the effects that constant voltage changes can cause.

The electrical and electronic equipment so that they can function properly depends on a constant voltage and frequency, with few variations in their values, this is one of the reasons why electric power utilities have a duty to deliver a good voltage and frequency. quality, within the specifications required by the standards.

Causes for variations and voltage drops.

Falls and variations in electrical voltage can occur due to several factors, including consumption during the day, some factors are:

During the entire length of a distribution network, it is not possible to maintain the same voltage in all installations, because over all of them there will be a voltage drop, however small, so at the end of the network it will be a considerable difference from the beginning.

Another factor that can cause the voltage drop in the network is the distance, due to the resistance of the cables, causing the voltage to fall progressively from the generating source, which in the case of electrical distribution is the transformer. The same can happen inside the installation if the distances between the QDC and the loads are large.

Sine wave, voltage variation.

Washing machines, microwaves, air conditioners, vacuum cleaners, among other equipment used in homes can cause an increase in current when they are activated, which consequently changes the voltage value, however, when this variation reaches its highest value it ends up being a very short period of time.

There are situations in which the voltage inside the installation is low, but this value can occur due to the source that comes from the concessionaire, which can be identified by the direct voltage on the concessionaire’s meter.

Effects of voltage variation.

Voltage fluctuations and drops can undoubtedly be detrimental to the electrical and electronic equipment in the installations, but small variations, not in most equipment, do not cause problems, because most equipment is designed to withstand a variation in its voltage of up to a maximum of 10 %.

It is important to point out that many pieces of equipment are bivoltine, that is, it works on 127V or 220V, and some have an external selector switch, while others make this change internally automatically.

Equipment that is exposed to a voltage above its limit, for which it was designed, suffers an overload and it is in this situation that the equipment is lost, as its internal circuit is damaged and ends up “burning”.

However, in cases where the devices are being connected to a voltage below their limit, the possibilities of “burning” are rarer, but it does not mean that they have no problems.

Some appliances to keep them running on a low power end up being forced, like those with motors, because the starting voltage is not enough, so without being able to start, the motor has a very low impedance, which ends up requiring a much greater current than necessary, with the operation remaining that way, in the motors mainly, there is heating that is harmful to the devices.


There are devices that are able to protect electronic equipment from possible damage due to variations and voltage drops, such as breaks. exit, in addition, to avoid burning the equipment.

When buying this device, be aware of the power that the UPS supports, as each equipment dissipates different power.
Please note that the protection devices mentioned above do not solve the problem of voltage variation or drop in the electrical installation.

When the voltage is not within the conditions that the concessionaire has to guarantee, that is, maximum and minimum voltage values, available in the energy bill and which may vary according to each region, the first step to be taken is to ascertain the voltage straight into the pattern, where the energy is coming from.

If the problem is being straightforward in the standard the responsibility is of the concessionaire, who must be notified, from then on the necessary measures will be taken.

If variations or voltage drops are occurring within the installation, tests and measurements must be made for all circuits, in this situation an electrician must be called in to identify the problem.