# Rated vs Nominal (Electrical Term)

#### MrAbh

##### Senior Member
Good morning to all,
Would you please help me in understanding the difference between Nominal and Rated (Voltage, Frequency, Output etc.).
These two terms, i oftern come across while translating any technical particulars related to Transformers, resistors.
Any help would be greatly appreciated.

Merci d'avance.
Bonne journée!

• If I am right (I sudied electricity engineering), a nominal value is a value such that the device works in ideal conditions; it was designed with the nominal value in mind. For example, a transformer was built for the nominal tension 380 V, nominal frequency 50 Hz; the actual values can be imposed externally. A rated value is some intrinsic property that you measure. At the given nominal tension and frequency, the transformer has a rated impedance of 1 Kilo Ohms.

On second thoughts (I checked in dictionaries), my explanation above is wrong. There doesn't seem to be a difference between "nominal" and "rated". They can denote the normal usage value or the largest bearable value.

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Whenever i searched dictionnaries, i have found the same french word for Rated and Nominal.
I also tried to find out the exact difference between these two from my engineer friends. They told me that Nominal means the normal condition in which an equipment functions, in case of voltage, it is the voltage under normal conditions.
Rated voltage means the highest voltage it could have. Though, i am still not sure.
For rated voltage, i also saw RATED VOLTAGE RMS (Root mean square) some where i found Tension Efficace in French.
Have a nice day!!!

Be careful about using the "RMS" and "Efficace" qualifiers, this is a technical issue. It is independent of "Nominal" and "Rated" properties and is only relevant in alternative current. It rather denotes the way these quantities are defined.

In AC, the tension varies all the time (with a 50/60 Hz frequency), and it is conveninetly expressed by an equivalent DC tension that has the same thermal effect. This is the so called RMS value, Efficace in French.

"Rated voltage" is "tension nominale".
"Rated voltage RMS" is "tension efficace nominale".

If you are maths litterate, RMS means 'the square root of the average over time of the squared value'.

Thanks for these clarifications.
Really, i would have applied the general meaning in all the cases. I would take care of it in future, in fact, i am going to have more of it soon. So, i need to be correct and precise in my translation. Meanwhile, i will keep searching for the good knowledge of these terms.
Thanks YvDa.

Wikipedia is often a good starting point. When you are on a page, sometimes it is avaialble in several languages.

" ominal means the normal condition in which an equipment functions, in case of voltage, it is the voltage under normal conditions."
"Rated voltage means the highest voltage it could have."

I think the above is correct, as explained here :http://answers.yahoo.com/question/index?qid=20071022211737AAV05Y0

"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."

I understand your problem when it comes to understand the difference between "rated" and "nominal", as they are sometimes used as synonyms.
In fact, it all depends on the margins used to design a given piece of equipment.

A simple way to look at it is to compare a family car and a sports car, having maximum (rated) speeds of repectively 140km/h and 250 km/h :
If you consider that both cars have to be used on a highway at 120 km/h (nominal speed), the 'rated speed' of the family car will be very close to its 'nominal speed', while there is a big difference between the 'rated speed' and the 'nominal speed' of the sportscar.

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

I hope this helps ....

I think the above is correct, as explained here :http://answers.yahoo.com/question/index?qid=20071022211737AAV05Y0

"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 ....

Surely, it is of great help. The context i have right now, it is the best i can have as for Nominal Voltage, i have already said Tension Nominale. And there is a separate quote for Maximum Voltage. So, for Rated Voltage, your proposition seems very appropriate to me. Thanks Magonette and YvDa again

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

"voltage" existe en Français mais est peu usité. Préférer "tension".