Nominal voltage is the voltage level of an electrical power system. It is sometimes referred to as system voltage. The voltage between the exterior lines in a three-phase system is known as the nominal voltage. The rated voltage is the voltage range for which the equipment is meant to function under steady conditions, providing reliability. Outside this range, the equipment may not operate properly and could possibly fail.
Nominal current is the amount of electricity that flows through the circuit per unit time. The term "nominal" means "of a given size". So, nominal current is the current capacity of the circuit divided by its cross section. If the load increases, then the current should be increased too. Otherwise, the circuit will be overloaded and might fail.
In household wiring, the term "nominal" refers to the voltage across the hot wires with no lights or appliances plugged in. This is usually 120 volts AC (or 240 volts DC), but it can be any other number depending on the manufacturer or regulator. In fact, the voltage needed to light up most lamps is almost always higher than the "nominal" voltage because some electricity is lost when changing from AC to DC or vice versa. The ratio of peak voltage to average voltage is called the harmonic content. Most electricity in North America has about 40% of its energy at 60 Hz and 20% at 400 Hz; so average voltage is 80% of 120 or 96 volts, and peak voltage is 160 or 200 volts.
When referring to a voltage level, the standard value is referred to as nominal voltage. If the nominal voltage is 220 volts, the real voltage might be 5 or 10% higher or lower. Voltage refers to the force between two objects; therefore, it can be thought of as pressure multiplied by area (or mass). As with other pressures, such as air pressure or water pressure, there will be a maximum value for voltage before something gives way.
Nominal voltage is the name given to the amount of electricity that flows through a circuit even though some of this current may be lost in resistance. The term "nominal" comes from the fact that the actual voltage across any two points in a circuit is never exactly the same. If it was, then these points would have no potential difference between them, which would make them useless for carrying electrical charge or current. Since they do carry current, the voltage at any point is less than that at another point in the circuit. This means that there is more voltage being carried by those parts of the circuit where there are more loads connected, which is why power supplies usually have a rating for their nominal voltage.
The difference between the peak voltage and the average voltage of an electrical signal is called its peak-to-peak voltage.
The nominal voltages of 120 and 240 volts are used to identify a voltage class for residential structures. Other voltages include the high or low voltage ratings of light bulbs, appliances, electronics, and so on. The actual voltage delivered to an appliance may be higher or lower than its listed rating because power consumption varies depending on how it is used. For example, a light bulb can burn out if it is always plugged in even when not needed, so it makes sense that it would want to use as little power as possible when not being viewed directly beneath it.
Nominal voltage is the term used to describe the direct current (DC) supply voltage provided by a power station for distribution over a network. This is usually 125 or 250 volts but can be any value between these limits. The term does not apply to the voltage actually supplied to an individual piece of equipment or circuit, which might be much less if it performs some of its functions during periods when the power source is off or reduced in magnitude.
For example, a household electrical system is said to have a nominal voltage of 120 volts because this is the value of the DC supply at which point further reductions in voltage will not cause dangerous conditions such as electric shock. However, the voltage across any given wire within the house may be significantly less since many circuits require only a small amount of current.