What is Overvoltage?
When the voltage in a circuit or part of it is raised above its upper design limit, this is known as overvoltage. The conditions may be hazardous. Depending on its duration, the overvoltage event can be transient—a voltage spike or permanent, leading to a power surge.
What is Undervoltage?
Undervoltage occurs when the average voltage of a three-phase power system drops below the intended levels and is sometimes referred to as a brown-out. Operating in undervoltage conditions can drastically reduce the life of the electronic equipment and lead to premature failure.
Undervoltage conditions are usually caused by undersized or overloaded utility and facility transformers. During peak demand periods and/or when the utility is experiencing problems, the demand for power exceeds the capability of the transformer and as a result, the voltage drops.
The top five causes of Overvoltage.
Power system surges. Due to poor regulation of the power source or power utility company, voltage fluctuations, either over or under, may occur. This may cause serious damage, especially to electronic or computer-controlled equipment. In this case, special attention should be given to this equipment to ensure safe usage.
Insulation Failure. The most common form of insulation failure is when there is grounding of the conductor. Failure takes place when there is no insulation between the line and the ground. So, the part of the conductor that is grounded to the earth allows the current to flow downward.
Arcing Ground. This happens when there is a presence of a sporadic arc in line-to-ground fault belonging to a three-phase system. Here, short-lived oscillations are produced in the system due to some changes in the voltage and the current load. This phenomenon may lead to serious problems like a breakdown of the insulation and may harm equipment connected to the power system.
Resonance. This occurs when the value of the inductive resistance in the power system becomes equal with the value of capacitive resistance.
External causes. Although many cases of over-voltage result from the internal causes as listed above, the highest surges are still contributed by some external causes. Lightning is one good example, which has already been cited as responsible for the high magnitude of surges, leading to very serious failures. An external factor such as lightning is capable of increasing the voltage by many times higher than the normal value. This is the reason why power systems and appliances should be protected with voltage protectors.
Causes of Undervoltage
Undervoltage comes from a drop in power supply voltage during surges. The easiest solution is to set the undervoltage parameter to a lower value and use a power supply that doesn't shut down or drop to near zero under power surges.
In order to test low voltage DC power, you must turn your multimeter to the proper setting on the range selector switch and put the test lead in the proper jack.