Overheating can cause electrical and electronic components (e.g., circuit boards) to fail prematurely if the voltage is too high. The voltage level provided can reach a threshold where it is so high that it damages a motor, however this level is significantly greater than that for electronics. For example, a 7-volt supply will not damage most motors, but a 14-volt supply will be far beyond what most devices are designed to handle.
What causes voltage levels to increase in an electrical system? There are two main factors that can cause voltage levels to rise: load and power source. Load refers to anything that uses energy from the power source -- including the equipment being used to generate electricity. Power source means the device generating the power (such as a generator or battery).
If load increases on a system then so does the voltage required. This is because the only thing keeping voltage levels down is the resistance of the conductors feeding power into the load. As long as this resistance remains constant, then voltage will always rise when more load is placed on the system. For example, if you were using a 12-volt car battery to start an engine using a wire with 100 ohms of resistance, then the voltage would rise to 13 volts before dropping back down to 12 volts when the engine stopped running. However, if you added another motor to the system which used some of the battery power, then both motors would get 13 volts even though only one was running.
In general, the variation between the greatest and lowest voltages should not be greater than 4% of the lowest voltage. Increased imbalances may result in overheating of components, particularly motors, and occasional shutdown of motor controllers. An imbalance as low as 2% has been reported for large motors driven by inverters.
An imbalance of 6V or more indicates a defective meter or poor wiring practices. Imbalance due to one load being higher than another will cause both loads to run longer than they should, which could lead to damage to the equipment if it isn't done regularly. This type of imbalance can only be detected by a properly functioning voltage meter.
Imbalance due to one circuit being shorter than another will cause that circuit to deliver more current than it should, which could also lead to damage of the equipment if it isn't done regularly. For example, if one branch of an electric heater circuit is shorter than another, then that circuit will try to deliver more current than the other, which could overload the breaker that controls power to the whole circuit. This type of imbalance can only be detected by looking at the voltage readings on a voltage meter.
If you are unsure whether an imbalance is harmful, contact a qualified electrical contractor for advice. He or she will be able to tell you how serious the imbalance is and what needs to be done about it.
If there was no risk from the voltage, no one would ever print and show warnings that said: DANGER—HIGH VOLTAGE! As a result, there is a risk of excessive voltage, which can produce enough current to cause harm or death. In contrast, if a body has a greater resistance, less current will flow for any given voltage. So, a sign saying CAUTION—LOW RESISTANCE will not be as effective at warning people away from dangerous situations.
The reason signs with these phrases are required by law is because power lines need to be kept clear of vegetation so that they can conduct electricity properly. If they come into contact with trees, bushes, or other high-resistance materials, then they can cause erosion, damage to property, and even death.
Power companies must also keep an eye out for animals like cows, pigs, and sheep that might decide to wander onto their land. If a cow or pig gets shocked by a power line, it could potentially suffer a fatal heart attack. Power companies need to know about these animals so they can take measures to prevent this from happening. For example, they may want to put up fences or clear vegetation away from power lines if these animals are likely to come into contact with them.
Finally, power companies must make sure that nobody tries to steal their electricity by climbing onto their towers with the intention of putting themselves in contact with the lines.
Increasing the voltage over an appliance's typical working voltage can induce an electrical current arc within the appliance, and the heat generated by the arc can destroy the electronic circuit boards and other electrical components. Applying excessive voltages to appliances with low electrical resistance (such as light bulbs) may cause the bulb to explode.
The maximum allowable voltage for household use is 120 volts AC (60 volts DC). Appliances that are designed to operate on lower voltages should not be used with voltages greater than they were designed for. An electric heater, for example, is likely to burn out if its voltage is increased without a corresponding change in its power supply. A fuse or circuit breaker must be used to protect wiring from overheating and damage caused by arcing. Wiring should be allowed to cool before being touched by hand. If an appliance has been powered down then it should be re-tested after any repairs have been made.
High voltage comes in two forms: line voltage and transformer voltage. Line voltage is the normal voltage of the power distribution system, usually 120 volts or 240 volts. Transformer voltage is the voltage produced by a transformer. Transformers take the voltage supplied by the utility company and reduce it for use with smaller equipment. For example, a transformer on an air conditioner reduces the high voltage of the utility company from 240 volts to 12 volts.