Dan Sprute
New member
Many, many folks, especially old folks, refer to nominal voltage as 110 220 and 440 Volts.
According to the 2005 NEC Voltage, nominal will be 120, 240 and 480 Volts.
? Article 100 Voltage, nominal (definition)
? 220.5 Calculations and
? Annex D Examples
This is a good call because 120V times the square root of 3 equals 208V rounded, and 480V divided by the square root of 3 equals roughly 277V. That doesn?t work out if you use 110V or 115V or 440V or 460V. So the NEC specifies the proper voltage levels so that calculations work out mathematically accurate for wye connected systems.
This was not true of the NEC previous to 1984. If you look at Article 900 B (Examples) in the 1981 NEC, Voltage, nominal to be used for calculations was specified as 115V and 230V.
I have copies of the NEC going back to 1953 and the same is true back to that point. I have reviewed the first NEC circa 1889 which is/was posted on Mike Holts web site. It makes no mention of specific nominal voltages.
My question is at what point, if ever, did the NEC last specify nominal voltage to be 110V and 220V. Do you know? Or if not, do you know where there would be an archive of past NEC books, available for review. It is interesting to review the older codes. They can help you understand the design that went into wiring older existing structures. For instance I would also like to review the codes that required bathroom light switches to be located on the outside of the bathroom entry, and the requirement for kitchen appliance circuits when only one was required per kitchen. Knowing when the article was first changed would clue an electrician in on what to expect in a home or commercial building determined by the year that it was built.
According to the 2005 NEC Voltage, nominal will be 120, 240 and 480 Volts.
? Article 100 Voltage, nominal (definition)
? 220.5 Calculations and
? Annex D Examples
This is a good call because 120V times the square root of 3 equals 208V rounded, and 480V divided by the square root of 3 equals roughly 277V. That doesn?t work out if you use 110V or 115V or 440V or 460V. So the NEC specifies the proper voltage levels so that calculations work out mathematically accurate for wye connected systems.
This was not true of the NEC previous to 1984. If you look at Article 900 B (Examples) in the 1981 NEC, Voltage, nominal to be used for calculations was specified as 115V and 230V.
I have copies of the NEC going back to 1953 and the same is true back to that point. I have reviewed the first NEC circa 1889 which is/was posted on Mike Holts web site. It makes no mention of specific nominal voltages.
My question is at what point, if ever, did the NEC last specify nominal voltage to be 110V and 220V. Do you know? Or if not, do you know where there would be an archive of past NEC books, available for review. It is interesting to review the older codes. They can help you understand the design that went into wiring older existing structures. For instance I would also like to review the codes that required bathroom light switches to be located on the outside of the bathroom entry, and the requirement for kitchen appliance circuits when only one was required per kitchen. Knowing when the article was first changed would clue an electrician in on what to expect in a home or commercial building determined by the year that it was built.
