nominal voltage

[yukonjack_99674]

Can anyone explain to me what is ment by nominal voltage? If you have a 120/240 service, is your nominal voltage the 120 legs to ground? or the 240? I do not understand how you can get 240 to ground. From what Ive read, the circuit is based on the equipment to be used. In other words, if you have 240volt heaters the circuit is considered 240v nominal yet what would be your reference point. You see nominal voltage all over the code book, I must have a thick head. Thanks

[480sparky]

From Art. 100:

Voltage, Nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.

(blue highlight is mine)

It means a 240-volt circuit may not be exactly 240.00000 volts.

[ray cyr]

Nominal means "named". A 120/240 volt system has that "name" because of the RMS value.

[weressl]

Originally Posted by yukonjack_99674

Can anyone explain to me what is ment by nominal voltage? If you have a 120/240 service, is your nominal voltage the 120 legs to ground? or the 240? I do not understand how you can get 240 to ground. From what Ive read, the circuit is based on the equipment to be used. In other words, if you have 240volt heaters the circuit is considered 240v nominal yet what would be your reference point. You see nominal voltage all over the code book, I must have a thick head. Thanks

Nominal is the system voltage at the distribution point, say 120VAC.
Nominal utilization voltage is the volateg at the user point, that is on the nameplate of the equipment, say 115VAC.

Voltage ranges are the defined highs and lows around the above numbers thata re expoected to be maintained, so the systems and supplies are to be designed to comply with those limitations.

Range A:
Max. Utilization and Service: 126VAC
Min. Service: 114VAC
Min. Utilzation: 110VAC

Range B:
Max. Utilization and Service: 127VAC
Min. Service: 110VAC
Min. Utilzation: 106VAC

So the ranges define the acceptable limits around the nominal.

[LarryFine]

Expected, average, normal.

[Pierre C Belarge]

Originally Posted by yukonjack_99674

Can anyone explain to me what is ment by nominal voltage? If you have a 120/240 service, is your nominal voltage the 120 legs to ground? or the 240? I do not understand how you can get 240 to ground. From what Ive read, the circuit is based on the equipment to be used. In other words, if you have 240volt heaters the circuit is considered 240v nominal yet what would be your reference point. You see nominal voltage all over the code book, I must have a thick head. Thanks

Nominal voltages are like the standard voltages that are produced by the utility company.
Such as 120/240, 120/208, 277/480, 347/600.

Lets say the nominal voltage to the building is 120/240. The Actual Voltage may be 115/235 or something like. The different in actual voltage and Nominal voltage can be caused by many things, such as voltage drop or the transformer tap, etc...The actual voltage can even be higher in value than the nominal voltage.

And then there is voltage to ground. That would be the measurement taken from an ungrounded conductor to the equipment ground.

See Article 100,
Voltage(of a circuit)
Voltage, Nominal
Voltage to Ground

See 220.5(A)Voltages.

[yukonjack_99674]

Thank you everyone for the help, I think I have it now. Was'ent that hard after all (once it was explained) thanks