# Rated and nominal AC voltage?

1.What is Rated AC voltage? Why we would like to state Rated instead of Nominal?

2.What is Nominal AC voltage?

3.Explain rms value for AC voltage. What is it's relation to Rated/Nominal Voltage?

### 5 Answers

- EE68PELv 61 decade agoFavorite Answer
Rated AC voltage might be the nominal voltage at which a piece of electrical equipment is designed to operate. In the case of a light, heater or motor, the operation at the rated voltage would provide the rated performance. Most equipment can operate at 5 or 10% above or below the rated voltage without much change in performance.

Rated voltage could also be the maximum voltage that a type of wire, plug, socket or circuit breaker is designed for. In that case, the rated voltage may be considerably higher than the nominal voltage.

Nominal voltage is the standard value that is used when referring to a voltage level. If the nominal voltage is 220 volts, the actual voltage might be 5 or 10% higher or lower.

The RMS value of an AC voltage is the effective value. It is the value that is usually stated when refering to an AC voltage. RMS stands for root mean square. RMS is calculated by calculating the square root of the average of the instantanious voltages making up one cycle of the waveform. It can be calculated or measured for any waveform including square waveforms and distorted sine waveforms. For an undistorted sine wave, the RMS voltage is the peak voltage divided by the square root of 2.

Nominal and rated AC voltages are usually RMS values.

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- Anonymous4 years ago
It is common habit to speak of extracting current, but it is misleading, in that it implies the device is acting in a positive fashion. It is more useful to regard the appliance (whether AC or DC) as a passive load, accepting what gets fed to it. The typical device will therefore draw an excessive current when too high a voltage is supplied and too little current to function properly when the voltage supply is too low. It follows from this that the appliance does not "extract" a working voltage from a voltage supply that is too high (unless it has an input stage that is specially designed to achieve this).

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- 4 years ago
"Rated voltage" could also be the maximum voltage that a type of wire, plug, socket or circuit breaker is designed for. In that case, the rated voltage may be considerably higher than the nominal voltage.

"Nominal voltage" is the standard value that is used when referring to a voltage level. If the nominal voltage is 220 volts, the actual voltage might be 5 or 10% higher or lower."

So in French, "rated voltage" is sometimes used for "voltage nominal", but it is also translated as "voltage maximum admis"

I hope this helps ....

Source(s): Alireza hajargasht- Login to reply the answers

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- 5 years ago
The 'rated voltage' is the maximum voltage that the circuit-breaker can interrupt safely and without being damaged by excessive arcing.

The 'nominal voltage' is the voltage for which the circuit-breaker is intended to be used.

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