A voltage rating is an evaluation based on research and experimentation that help determine how much voltage can be safely utilized by a particular device or form of wiring over the life of the device or wiring. For electrical and electronic devices, this rating is determined during product development and testing by increasing the voltage levels until the devices break down or begin malfunctioning. The voltage rating is not the maximum at which breakdown occurs, it is a percentage of the maximum and is intended to be a safe level for extended use. For wiring, the voltage takes into consideration the materials used to construct the wiring, the thickness of wires and the intended use of the wiring. A voltage rating scale has been established for all forms of electrical wires.
The main purpose of a voltage rating is to ensure that the user of the wiring or the device can reasonably expect to use the material for its intended purposes and not encounter danger to the user or damage the device. From this perspective, the rating will specify how much electrical current can safely be carried through the wiring, and it will define the type of current that can be safely conducted through the wire. Following the standard set by the voltage rating greatly diminishes the chances of overheating and electrical fires.
There is no commercially manufactured device that has not been tested and certified with a voltage rating. Depending on the construction and intended use of the device's wiring, the rating could vary greatly. For example, voltage ratings for mineral-insulated (MI) copper cable usually is close to 1,000 volts. The wiring for table lamps and other small household appliances usually is much lower.
By setting a rating that specifies the highest voltage that the wiring can carry and still operate within acceptable safety limits, governments and other organizations can set standards for wiring depending on its applications. Wiring that is used in the electrical system of a residential home, for example, typically must meet specific standards and be within a certain range. The same is true for wiring in public buildings. Many types of machinery used in the production of goods and services must also contain wiring that meets standards and have a voltage rating that is considered reasonable for the level of current that the machine will need to function properly over the long term.