Voltage Ratings: 110/115/120, 220/230/240 or 440/460/480

Merry Christmas

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
This subject comes up a LOT in this and other forums, so I thought it would be a good idea to make it a "Sticky" that can be found and referred to easily when it comes up.

There are two "standards" for voltage in North America depending on which END of the wire you are looking at; "Distribution Voltage" (also called "Service Voltage") and "Utilization Voltage", both set forth in ANSI (American National Standards Institute) Standard number C84.1, backed up by IEEE (Institute of Electrical and Electronics Engineers).

The official Distribution Voltage standard for single phase is 120 and 240V, for 3 phase it is 208, 240, 480 and 600. It has been this way since the 1930s after the REA (Rural Electrification Act) during the Great Depression went to bring electricity to farms and rural areas, because the Utilities all did what they wanted to and they didn't see enough profit in it. But because each utility was different at the time, (i.e. 110, 115, 117, 120, 125, etc. etc.), and the REA didn't want to have their service trucks carry around multiple voltage ratings, they picked a "middle ground" of 120/240V and called that the standard. It has been that way since. Later on, standards for the Utility industry came along and added that no matter what they give you, it has to be within +-5%. So for a 120V system, that is between 114V and 126V; for 240V it is 228 to 252V, etc. etc. However many of the older systems still deliver what they used to deliver, regardless of what it is officially called, so yes, there are still pockets of 110V, 220V and 440V out there.

For that reason, industry organizations for manufacturers, such as NEMA (National Electrical Manufacturers Assoc.) developed their OWN standards for the devices that use electricity, and their standard was +-10%, but based on a LOWER voltage, because there is an expected voltage drop from the Service Entrance to where the device connects. So for 120V Distribution, the Utilization voltage is 115V; for 240V it is 230V, for 208V it is 200V, for 480V it is 460V and for 600V it is 575V.

So how that works out is that a MOTOR for example will be built for 230V, +-10%, so it can accept anything from 207 to 253, and because the Distribution Voltage is 228 to 252V, it fits right in. But also if the Utility was still putting out 220V instead of 240V, the LOW end of their range would be 220-5%, so 209V, still within the acceptable range of the Utilization standard.

People however are not swift on the change though, so LOTS of people still refer to residential as being 110/220, or 115/230 or 120/240 (inset joke from the movie "The Money Pit" where Michel Keaton says "220/221.whatever it takes..."). But OFFICIALLY, it is supposed to be 120/240V.

While we are on the subject of "officialdom"; When describing distribution systems that have more than one voltage available, there is a "convention" in the description that should be used to help avoid confusion.
  • If the subject is SINGLE PHASE, the LOWER voltage is listed first, followed by the higher . So a residential single phase system is described as "120/240V".
  • If the subject is THREE PHASE, the HIGHER voltage is listed first, followed by the lower. So 480/277V would be correct, 277/480V would not. This is especially important because we have 240/120V 3 phase 4 wire systems available. So by calling it 240/120V you are differentiating it as three phase, compared to 120/240V being single phase.
 

bwat

EE
Location
NC
Occupation
EE
I'm half-tempted to turn in my PE license for only knowing about 10% of this.

Seriously though, great info. Thanks for taking the time to post.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
  • If the subject is THREE PHASE, the HIGHER voltage is listed first, followed by the lower. So 480/277V would be correct, 277/480V would not. This is especially important because we have 240/120V 3 phase 4 wire systems available. So by calling it 240/120V you are differentiating it as three phase, compared to 120/240V being single phase.
Don't they usually include Y or D, such as in 480Y/277 or 240D/120?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
REA crews traveled through the American countryside, bringing teams of electricians along with them. The electricians added wiring to houses and barns to utilize the newly available power provided by the line crews. A standard REA installation in a house (post World War II) consisted of:

  • A 60 amp, 230 volt fuse panel, with:
  1. A 60 amp range circuit
  2. A 20 amp kitchen circuit
  3. Two or three 15 amp lighting circuits

A ceiling-mounted light fixture was installed in each room, usually controlled by a single switch mounted near a door. At most, one outlet was installed per room, since plug-connected appliances were expensive and uncommon.
Wiring was performed using type NM (nonmetallic
sheathed cable), insulated with asbestos-reinforced rubber covered with jute and tar.


I also like to use this chart:
372CB66F-BAA5-4FAA-8C6A-9F92F33C15C0.png
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
REA crews traveled through the American countryside, bringing teams of electricians along with them. The electricians added wiring to houses and barns to utilize the newly available power provided by the line crews. A standard REA installation in a house (post World War II) consisted of:

  • A 60 amp, 230 volt fuse panel, with:
  1. A 60 amp range circuit
  2. A 20 amp kitchen circuit
  3. Two or three 15 amp lighting circuits

A ceiling-mounted light fixture was installed in each room, usually controlled by a single switch mounted near a door. At most, one outlet was installed per room, since plug-connected appliances were expensive and uncommon.
Wiring was performed using type NM (nonmetallic
sheathed cable), insulated with asbestos-reinforced rubber covered with jute and tar.


I also like to use this chart:
View attachment 2557797
Man that was fancy, around here you got a pull chain light and one receptacle per room! LOL!
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
...

The official Distribution Voltage standard for single phase is 120 and 240V, for 3 phase it is 208, 240, 480 and 600. It has been this way since the 1930s after the REA (Rural Electrification Act) during the Great Depression went to bring electricity to farms and rural areas, because the Utilities all did what they wanted to and they didn't see enough profit in it....
I thought it was a lot more recent than that. Motors still had nameplates of 440 volts for a 460 volt system in the 60s.
 
Last edited:

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Don't they usually include Y or D, such as in 480Y/277 or 240D/120?
No.
The ANSI standard is to include the Y, but it ignores the D. It is common for utilities to ignore the ANSI standard naming convention entirely.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
This subject comes up a LOT in this and other forums, so I thought it would be a good idea to make it a "Sticky" that can be found and referred to easily when it comes up.

There are two "standards" for voltage in North America depending on which END of the wire you are looking at; "Distribution Voltage" (also called "Service Voltage") and "Utilization Voltage", both set forth in ANSI (American National Standards Institute) Standard number C84.1, backed up by IEEE (Institute of Electrical and Electronics Engineers).

The official Distribution Voltage standard for single phase is 120 and 240V, for 3 phase it is 208, 240, 480 and 600. It has been this way since the 1930s after the REA (Rural Electrification Act) during the Great Depression went to bring electricity to farms and rural areas, because the Utilities all did what they wanted to and they didn't see enough profit in it. But because each utility was different at the time, (i.e. 110, 115, 117, 120, 125, etc. etc.), and the REA didn't want to have their service trucks carry around multiple voltage ratings, they picked a "middle ground" of 120/240V and called that the standard. It has been that way since. Later on, standards for the Utility industry came along and added that no matter what they give you, it has to be within +-5%. So for a 120V system, that is between 114V and 126V; for 240V it is 228 to 252V, etc. etc. However many of the older systems still deliver what they used to deliver, regardless of what it is officially called, so yes, there are still pockets of 110V, 220V and 440V out there.

For that reason, industry organizations for manufacturers, such as NEMA (National Electrical Manufacturers Assoc.) developed their OWN standards for the devices that use electricity, and their standard was +-10%, but based on a LOWER voltage, because there is an expected voltage drop from the Service Entrance to where the device connects. So for 120V Distribution, the Utilization voltage is 115V; for 240V it is 230V, for 208V it is 200V, for 480V it is 460V and for 600V it is 575V.

So how that works out is that a MOTOR for example will be built for 230V, +-10%, so it can accept anything from 207 to 253, and because the Distribution Voltage is 228 to 252V, it fits right in. But also if the Utility was still putting out 220V instead of 240V, the LOW end of their range would be 220-5%, so 209V, still within the acceptable range of the Utilization standard.

People however are not swift on the change though, so LOTS of people still refer to residential as being 110/220, or 115/230 or 120/240 (inset joke from the movie "The Money Pit" where Michel Keaton says "220/221.whatever it takes..."). But OFFICIALLY, it is supposed to be 120/240V.

While we are on the subject of "officialdom"; When describing distribution systems that have more than one voltage available, there is a "convention" in the description that should be used to help avoid confusion.
  • If the subject is SINGLE PHASE, the LOWER voltage is listed first, followed by the higher . So a residential single phase system is described as "120/240V".
  • If the subject is THREE PHASE, the HIGHER voltage is listed first, followed by the lower. So 480/277V would be correct, 277/480V would not. This is especially important because we have 240/120V 3 phase 4 wire systems available. So by calling it 240/120V you are differentiating it as three phase, compared to 120/240V being single phase.
Figure I would add the ANSI C84.1 tables for reference.

1631743664230.png
1631743774223.png
1631743794421.png
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I don't see how there could be 240/120V three phase delta.
This is the description for a delta with one center tapped winding. These are often called wild or high leg systems, because it produces two line to neutral voltage of 120V and one line to neutral voltage of 208V.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
This is the description for a delta with one center tapped winding. These are often called wild or high leg systems, because it produces two line to neutral voltage of 120V and one line to neutral voltage of 208V.
I am familiar with high leg services, but I have not seen them denoted as 240D/120.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I am familiar with high leg services, but I have not seen them denoted as 240D/120.
It is only 240/120, the D is not used.

Per the ANSI naming convention three phase systems should have the L-L voltage then the L-N voltage, while single phase are the opposite way.
Many utilities do not follow this convention, so it can be confusing. For years I have tried to include the number of phases and the number of wires when I use voltages in a discussion, particularly with 240V.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
It is only 240/120, the D is not used.

Per the ANSI naming convention three phase systems should have the L-L voltage then the L-N voltage, while single phase are the opposite way.
Many utilities do not follow this convention, so it can be confusing. For years I have tried to include the number of phases and the number of wires when I use voltages in a discussion, particularly with 240V.
So 240/120 for three phase with a high leg and 120/240 for single phase? That seems easy to misunderstand; I will always include "high leg" in the descriptor if that's what it is.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Great post, this standard at one point was going to be used by almost all the Americas but now its shrank back to just the US.
and all of our neighbors to the south pretty much follow something similar except one thing
they use 220Y/127 instead of 208Y/120.
It would be cool to see the equivalent chart/ standards that they use south of us say in Mexico or Brazil.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I'm half-tempted to turn in my PE license for only knowing about 10% of this.

Seriously though, great info. Thanks for taking the time to post.
Don’t feel bad. I worked in this industry for 20+ years before I found out there was a standard conventional nomenclature for that. It’s not taught well. Many of the PEs I have seen use it incorrectly were stunned to find out this standard existed. Years ago when I had SKM power system software right after it first came out, I noticed they had it wrong (referring to 277Y480) and when I pointed it out to them, they wanted to argue that there was no standard. They fixed it.
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
Good post. I sort of knew much of this but not so much detail. I tell many lay people about 120 with its low & high ranges & same for 240.

I ran power to a soft drink box years ago. It’s nameplate specified 120 but had a footnote I never saw anywhere else. It stated that the appliance would operate from a minimum of 90 volts to a maximum of 130 volts.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
This is the description for a delta with one center tapped winding. These are often called wild or high leg systems, because it produces two line to neutral voltage of 120V and one line to neutral voltage of 208V.
And note that having initially defined neutral in a way that does not work in this situation (equal potential difference to all ungrounded wires) the NEC gives the center tap wire of the high leg delta the courtesy title of neutral. Without that I am sure electricians would never have been comfortable with any alternative terminology. :)
 
Top