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Thread: 440, 460, 480 volts

  1. #1
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    440, 460, 480 volts

    Why do some EC's refer to 480 volts as 440 or 460 when it is actually 480? EC's seem to use them interchangably. Also, I've seen panelboards marked 440 and 460 volts. Can anyone explain this? Thanks.

  2. #2
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    With rare exception, electrical equipment has the tolerance to consider these numbers interchangeable, like 110, 115, or 120 volts.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  3. #3
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    I don't usually work with 480 but 110 being changed to 120 some years back is the same ratio as 440 to 480, and 115 X 4 is 460. I'm just using the math to make a guess though.
    Sam, San Francisco Bay Area

  4. #4
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    Officially (according to ANSI) there are two voltage references; Distribution Voltage and Utilization Voltage.

    The Distribution Voltage in the US, for any new service, is supposed to be standardized on 480Y277V 3ph 4wire (in that voltage class of course). But compared to how long Electric Utilities have been in operation here, that is a relatively new occurrence. So because there was no previous national standard, every utility had their own idea as to what the "proper" voltage was for decades. For some it was 440V, others 460V, others 480V and even a few were 550V. Heck, some were 2 phase, some were 25Hz etc, etc. The movement to standardize started a while ago (1970's?), but it would be hellaciously expensive for every existing system to be replaced, so most are left as-is and called "legacy" systems. As their transformers and equipment fail, most are being upgraded to 480Y277V now.

    The Equipment Voltage, which is the design voltage for new motors and other things that use 480V 3 phase, is actually 460V. This serves two purposes; it allows for voltage drop at the motor terminals and it falls within the NEMA MG-1 tolerance specifications (+- 10%) for the legacy systems that are still out there. For example, 440 +10% is 484, 480 - 10% is 432 so 460 falls smack dab in the middle and everyone is happy. The only time you will see 440V on a motor now is either a really old motor or a foreign manufacturrer who has no clue (for example, Chinese knock-off junk peddlers).

    But a lot of people get confused, especially people from other countries where issues of legacy distribution systems are uncommon. So they read 460V is the common motor voltage and go along thinking that is the distribution voltage. Other people learned 440 in school and have a hard time "un-learning" that. But it really isn't that big of a deal; we all know what it means.
    Last edited by Jraef; 01-09-08 at 03:01 AM.

  5. #5
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    Quote Originally Posted by Jraef
    The Distribution Voltage in the US, for any new service, is supposed to be standardized on 480Y277V 3ph 4wire (in that voltage class of course). But compared to how long Electric Utilities have been in operation here, that is a relatively new occurrence. So because there was no previous national standard, every utility had their own idea as to what the "proper" voltage was for decades. For some it was 440V, others 460V, others 480V and even a few were 550V. Heck, some were 2 phase, some were 25Hz etc, etc. The movement to standardize started a while ago (1970's?), but it would be hellaciously expensive for every existing system to be replaced, so most are left as-is and called "legacy" systems. As their transformers and equipment fail, most are being upgraded to 480Y277V now.
    The US has had standardized nominal distribution voltages (ANSI C84.1) since the 1930's. These voltages have changed over the years rising from 440V up to the present 480V.

    People that chose to describe voltage systems at levels such as 115, 230, and 460V are ignoring NEC2005 arcticles 110.4 and 220.5.

    But of course old habits are hard to break.
    Just because you can, doesn't mean you should.

  6. #6
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    Quote Originally Posted by Ken 6789
    Why do some EC's refer to 480 volts as 440 or 460 when it is actually 480? ...
    As others have said, 480v systems use at 460V - the motors are wound for 460V - about a 5% drop. So using 460V reference is reasonable.

    As for the 440V references, it's cause they are sloppy. Unless you are out at an older mine, maybe self generating farm, there hasn't been any 440V around since the 60's. Some seem to wear it as a badge of honor to use the old time reference - I guess it makes them wise old-timers.

    Quote Originally Posted by Ken 6789
    ... Also, I've seen panelboards marked 440 and 460 volts. ...
    Likely old panel boards. Probably no later than the 60's.

    carl
    Using the code for a design guide is a sign of incompetance

  7. #7
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    thanks for the replies. Also, those panelboards marked 460 or 440 volts are from the 40's and 50's era. making sense now.
    Last edited by Ken 6789; 01-09-08 at 12:56 PM.

  8. #8
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    What you call the voltage verses what voltage is actually connected are two different things.

    The nominal (name) voltage is assigned to a range of Voltages (of a circuit) that may be expected to be present.

    Article 100 does a pretty good job explaining the two.
    Bryan P. Holland, MCP

  9. #9
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    I worked at a Textile plant as a Millwright in the early 70's and we had 440 there, at least thats how I remember it.:rolleyes:

  10. #10
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    Quote Originally Posted by wshoard
    I worked at a Textile plant as a Millwright in the early 70's and we had 440 there, at least thats how I remember it.:rolleyes:
    Yeah, 440 very common in the 70's.

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