- Nominal Voltage Definition: Nominal voltage is the assigned voltage class of a circuit or system, used as a reference point for electrical systems.
- Rated Voltage vs Nominal Voltage: Rated voltage is the highest voltage equipment can safely handle, while nominal voltage is the designed operating voltage.
- Operating Voltage: Operating voltage is the actual voltage applied at equipment terminals, crucial for reliable equipment performance.
- Nominal Voltage in Batteries: A battery’s nominal voltage is a standard reference value, differing from its actual voltage depending on charge level.
- Importance of Voltage Safety Margins: Designers must consider safety margins to ensure equipment operates safely within the rated voltage range.
What is Nominal Voltage?
Nominal voltage is defined as the value assigned to a circuit or system to conveniently indicate its voltage class (e.g., 120/240 volts, 300 volts, 480Y/277 volts). The actual operating voltage can vary slightly from the nominal voltage while still allowing the equipment to work properly.
The word “nominal” means “named”. It is not the precise operating or rated voltage. i.e. a 240-volt circuit may not be precisely 240.0000 volts, and may instead operate at 235.4 volts.
A nominal quantity, such as length, diameter, or voltage, is the standard value used to name or refer to an item.
Nominal voltage serves as a reference for batteries, modules, or electrical systems, indicating the supply circuit system voltage to which a unit may be connected. It can be considered an “approximate” or “average” voltage level, though it is not technically the average.
Nominal Voltage vs Rated Voltage
Nominal voltage, also called system voltage, is the voltage level of an electrical power system. In three-phase systems, the voltage between the external lines is referred to as the nominal voltage.
The voltage range for which the equipment is designed to operate under the stable condition by giving reliability is known as rated voltage. Thus the rated voltage of any electrical equipment is the highest voltage at which equipment can function within its thermal limit without endangering the life of the equipment.
When designing the device, the designer should take the voltage safety margin into consideration for operation of equipment within the range of rated voltage.
The rated voltage must be higher than the nominal voltage to ensure the safe operation of the equipment. The difference should be sufficient to account for variations in nominal voltage on the power lines.
To have a better insight on rated voltage, consider the working of a circuit breaker circuit. An electrical circuit breaker is a switching device which can be operated manually and automatically for controlling and protecting an electrical power system. Depending on the insulation system of a circuit breaker, the rated voltage of the circuit breaker varies.
The circuit breaker is designed to operate at the highest RMS voltage, which is known as the rated maximum voltage of the circuit breaker. This value is above the nominal voltage for which the circuit breaker is designed and is the upper limits for operation. The rated voltage is depicted in kV RMS.
In short, the ‘rated voltage’ is the maximum voltage that the circuit-breaker can interrupt safely and without being damaged by unnecessary arcing. Whereas the ‘nominal voltage’ is the voltage for which the circuit-breaker is designed to be used.
Nominal Voltage vs Operating Voltage
The voltage at which equipment is being operated is known as operating voltage. For reliable working of equipment, it must be operated within the range of rated voltage. The operating voltage is the actual voltage applied at the equipment terminal.
A multimeter is used to measure the voltage at the equipment terminal. If the applied voltage is greater or lower than its rated voltage, the performance of the equipment is affected.
As a concluding example for 132 kV power system, a circuit breaker is installed with the following specifications. When the operating voltage is not within the range of rated voltage, equipment operation is affected.
Nominal Voltage – 132 kV
Rated Voltage – 132 kV +/- 10 % [118.8 – 145.2 kV ]
Operating Voltage – Can be in the range of 118.8 to 145.2 kV.
What is the Nominal Voltage of a Battery?
A battery is an electrochemical device which generates a voltage potential when placing metals of various affinities in an acid solution.
For example, a battery that has an actual voltage of 1.62 V but commonly it is referred to as a “1.5-volt battery”, which means that the battery has a nominal voltage of 1.5 V. Another example is the term “DC 12V” describes a 12V battery, regardless of whether it is fully charged (13.7 Vdc) or discharged (10Vdc).
