- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I always love when this subject comes up. In college, I had to do a term paper on this very subject, partially as "penance" for some back-talk to the professor. I thought at the time tht this was a slice of information that would be entirely useless to my future, yet I cannot now even count the times this subject has come up for me. You never know...
There are two main reasons why ANSI has two different voltage level "standards"; Distribution Voltage and Utilization Voltage. The first was already touched on; expected voltage drop at the load. The other one has a lot to do with history and politics.
In the 30s when the REA was established, electric utilities were still far flung and completely disparate, meaning there was no central authority strong enough to make them all adhere to a common standard. So for example using this subject, we had utilities that used 440V, 460V, 480V and 500V all over the map. Household voltage levels of course followed suit, 110, 115, 120, 125V etc etc. When the REA came in to bring power out to the farms (primarily), their workers had problems with carrying equipment that would be OK with whatever the local utilities supplied. So ANSI and other standards organizations came up with the compromised utilization standards we use today. A motor rated 460V is required to work equally well at 440V as it does at 480V (500V became an outlier because it was rare and has since disappeared). NEMA adopted these standards and they are still in use. The Distribution Voltage standard came later, but only applies to NEW systems being designed and installed, because it would be prohibitively expensive for non-conforming systems to be changed. So nearly everything that already existed was grandfathered in and to this day we still have different utility voltages in different areas, in fact we have different voltages in the SAME areas in some places as new systems overlap old ones.
There are two main reasons why ANSI has two different voltage level "standards"; Distribution Voltage and Utilization Voltage. The first was already touched on; expected voltage drop at the load. The other one has a lot to do with history and politics.
In the 30s when the REA was established, electric utilities were still far flung and completely disparate, meaning there was no central authority strong enough to make them all adhere to a common standard. So for example using this subject, we had utilities that used 440V, 460V, 480V and 500V all over the map. Household voltage levels of course followed suit, 110, 115, 120, 125V etc etc. When the REA came in to bring power out to the farms (primarily), their workers had problems with carrying equipment that would be OK with whatever the local utilities supplied. So ANSI and other standards organizations came up with the compromised utilization standards we use today. A motor rated 460V is required to work equally well at 440V as it does at 480V (500V became an outlier because it was rare and has since disappeared). NEMA adopted these standards and they are still in use. The Distribution Voltage standard came later, but only applies to NEW systems being designed and installed, because it would be prohibitively expensive for non-conforming systems to be changed. So nearly everything that already existed was grandfathered in and to this day we still have different utility voltages in different areas, in fact we have different voltages in the SAME areas in some places as new systems overlap old ones.