What Is Rated Voltage – Rated Voltage VS Nominal Voltage 

Looking for what is rated voltage, how rated voltage is different from Nominal voltage or rated voltage vs nominal voltage? Then you came to the right place.

What Is Rated Voltage 

Rated voltage can be characterized as the most extreme voltage at which the gadget can be operated securely. After additional expanding the voltage, the gadget may neglect to work and might be harmed forever. Thus, Rated voltage is the greatest voltage limit at which the gadget can be operated securely. 

Rated voltage is for the most part characterized by the resistance rate, where resilience is given in rate. The resistance shows the base and greatest reach. For instance, if the rated voltage of the gadget given is 100v with a resistance of 10%. It implies that the greatest will be 110v and the base reach will be 90v. The base reach shows that the gadget will neglect to work underneath 90v. While the most extreme breaking point shows that the gadget will neglect to work after additional expansion. The gadget should be operated in the reach, neither above nor less. The creators of the gadget give an information sheet where the rated voltage is referenced with % resilience. 

What is Nominal Voltage? 

Nominal voltage is worth doled out to a circuit or framework to assign its voltage class conveniently(e.g. 120/240 volts, 300 volts, 480Y/277 volts). The real voltage at which a circuit works can differ from the nominal voltage inside a reach that licenses satisfactory activity of gear. 

“Nominal” signifies “named”. It is not the precise working or rated voltage. for example, a 240-volt circuit may not be precisely 240.0000 volts, and may rather work at 235.4 volts. 

A nominal amount (for example length, breadth, voltage) is by and large the amount as per which something has been named or is, for the most part, alluded to. 

Nominal voltage is utilized as a voltage reference to depict batteries, modules, or electrical frameworks. This is the stock circuit framework voltage to which the unit might be associated. You may think of it as a “rough” or “normal” voltage level (even though it is not actually “normal”). 

Rated Voltage VS Nominal Voltage 

The voltage level of an electrical force framework is known as Nominal Voltage. It is otherwise called framework voltage. In 3-stage frameworks, the voltage between the outside lines is known as the nominal voltage. 

The voltage range for which the gear is intended to work under steady conditions by giving unwavering quality is known as rated voltage. Along these lines, the rated voltage of any electrical hardware is the most elevated voltage at which gear can work inside its warm cutoff without imperiling the existence of the gear. 

When planning the gadget, the planner should take the voltage wellbeing edge into thought for the activity of hardware inside the scope of rated voltage. 

The rated voltage esteem should be more noteworthy than the nominal voltage, for the protected working of the gear. The distinction between the nominal and rated voltages should be sufficiently enormous to contemplate the varieties in the nominal voltage on the electrical cables. 

To have superior knowledge of rated voltage, consider the working of an electrical switch circuit. An electrical switch is an exchanging gadget that can be operated physically and naturally for controlling and ensuring an electrical force framework. Contingent upon the protection arrangement of an electrical switch, the rated voltage of the electrical switch fluctuates. 

The electrical switch is intended to work at the most noteworthy RMS voltage, which is known as the rated greatest voltage of the electrical switch. This worth is over the nominal voltage for which the electrical switch is planned and is as far as possible for activity. The rated voltage is portrayed in kV RMS. 

To put it plainly, the ‘rated voltage’ is the most extreme voltage that the electrical switch can hinder securely and without being harmed by pointless arcing. While the ‘nominal voltage’ is the voltage for which the electrical switch is intended to be utilized.

Advantages of nominal voltage

  • With increasing transmission voltage, the size of the conductors is reduced (the cross-section of the conductors is reduced as the current required for transport is reduced).
  • The reduction in the loss of current load requirements reduces the results in better efficiency.
  • The low current voltage drop will be less as voltage regulation improves.


  • With increasing transmission voltage, the required insulation between the conductors and the grounded tower increases. This increases the cost of the line support.
  • With increasing transmission voltage, more space is required between conductors and ground. Therefore taller towers are required.
  • If the voltage transmission increases, more distance will be required between the conductors, so the crossed arms must belong.

The difference in electric potential

The difference in electric potential is similar to the force required to uncouple electric rates of opposite signs. The tension increases the more they grow total load, distance, and intercurrent resistance forces between loads.

It is defined as the difference between the electric potential of two elements in space to the difference between the potential electric intensity that has an overload in both aspects due to the influx of an electric field, branched by the degree of the same charge.


It could still be said that it is literally the work done for a unitary overload in the scope of one space to another, ups and downs of the sign. It is measured with a voltmeter, integrated and electric meter. The unit of measure for the electric potential difference is the volt (V).

Relationship of nominal voltage with hydraulic circuits

When we make comparisons with a hydraulic contour, the difference between two points in the electrical circuit is equal to the difference between two points in the hydraulic circuit.

The potential difference between the poles of the electrical producer is perceived as the difference in the height of the equivalent hydraulic contour calculations and the dissipation of the electrical force as the friction of the liquid with the internal walls of the tube.

In short, the strength of the electric current flowing in the conductor can be put about the speed of the flow of the liquid in the tube.

For example, when it comes to a generating source, the charges move between two points with different potentials and an electrical force.

Open circuit voltage (VOC)

This is the voltage that is read by a voltmeter or multimeter when the module is not connected to any load.

This voltage is used when testing modules fresh out of the box and is used later when performing temperature-corrected VOC calculations in system design.

Corrected VOC temperature

This value is necessary to ensure that when cold temperatures increase the VOC of an array, other connected equipment such as MPPT controllers or Grid-Tie inverters are not damaged.

This calculation is done in one of two ways. The first is to use the table in NEC 690.7. The second way is to do calculations with the temperature voltage coefficient and the coldest local temperature.

The effect of voltage variation in electric motors

Every asynchronous electric motor, whether three-phase or single-phase, has or should have a characteristic data plate. The engine manufacturer provides through this plate, information regarding the brand, model, series, geometry (frame), mechanical power, speed, etc. Regarding the electrical information that should be recorded, the supply voltage and frequency (V / f) stand out. Depending on the design power, these electrical parameters (V / f) set the standard for the development of others such as current, power factor, speed, torque, efficiency, among others.

While it is true that the motor manufacturer indicates a nominal (desired) voltage, the supply voltage available in the network may “differ” or not conform to what is indicated on the data plate. NEMA regulations suggest that this variation does not exceed ± 10%, and IEC regulations ± 5%. For example, for a three-phase motor, a “lagged supply voltage” can present the same value on all three lines or an unbalance between them. The same value on the three 205 VAC lines differs from the 208 VAC desired or indicated on the plate. And an unbalance is exemplified by having 208 VAC, 210 VAC, and 203 VAC in the three-phase supply.

The “lag supply voltage” can be due to external or internal causes, or a combination of both. As an external cause, there is the supply voltage provided by the electric company, in this situation the due claim must be raised to be corrected. As an internal cause, it is often attributed to poor electrical designs, disorderly installation growth, and false contacts in sectioning and switching elements such as circuit breakers, contactors, fuses, etc. 

Before indicating the effects that occur in an electric motor as a function of the voltage variation, it is appropriate to expand with some definitions:

Voltage: It is the difference in electrical potential applicable on the motor connection terminals so that the electrical energy “flows” towards the motor. For this technical document, the effects on a NEMA variation of ± 10% are considered.

Full load current: It is the electric current that flows through a motor when its nominal power is required. For example, when a 5 HP three-phase motor is required that mechanical power and in turn is connected to a nominal voltage of 208 VAC, the electrical current at that time “probably” will be 13.9 A. 

Starting current: It is the electrical current that flows through a motor at the moment just when it starts during milliseconds. Depending on the inertia and size of the motor, this time can be extended to minutes in large motors. Generally around a value of 6 to 7 times the full load current. For the previous example, we would have an approximate value of 97.3 A.

ncr memento temperature: Due to the Joule effect, the electrical resistance conductive materials offer the passage of the current, part of the electrical energy is converted into thermal energy dissipated.

Power factor: It is the relationship that exists between the apparent power (available in the electrical network) and the active power (usable in useful work), neglecting the magnetic effects ( reactive power ). Magnetic flux is required by a motor to establish an inductive effect but this does not add useful work. In addition, this parameter indicates the degree of phase difference that exists between the electric current and the voltage, the greater this phase difference, the lower the power factor, resulting in high reactive power. It oscillates between 0 and 1. A power factor close to 1 indicates a high use of the apparent power.

Efficiency:  It is the relationship between active electrical power and mechanical power output. Remember that active electrical power is transformed into thermal energy (by Joule effect) and motive energy. 

Starting torque: It is the rotational force that a motor must overcome at the moment of starting. The equipment must overcome the static inertial conditions and the load to which it is linked.

Synchronous speed: It is the speed of the rotating magnetic field that develops in the motor’s stator. This speed is proportional to the frequency and inverse to the number of magnetic poles obtained by the stator winding arrangement.

Mechanical speed: It is the speed on the rotor shaft, for asynchronous motors it will always be less than the speed of the rotating magnetic field. This is due to the dispersion of the magnetic flux in the induction process from the stator to the rotor, in which the latter is always “lagged”.

Slip percentage: It is the percentage difference that exists between the synchronous speed and the mechanical speed.

Share your love