Using too simplistic of a breakdown of just low, medium, + high voltage doesn't work out very well. . As an inspector, I perfer letting the NEC dictate the breakdown rather than IEEE. . But if your job deals with IEEE standards more often than you deal with the NEC, then I would use IEEE. . The category limits that you use should to provide you with usable categories for your particular job.
In the classes for electrical construction apprentices that I teach, I list these categories:
EQUIPMENT
0-600 . . Standard
601-2000 . . Low Industrial
2001-35,000 . . Medium Industrial
35.001 & up . . High Industrial
The categories come from the NEC + manufacturers.
You'll notice that T310.13(A) writes down what we already knew, that standard insulations are rated up to 600v.
490.2 lists more than 600v as "high voltage" equipment but that category then gets subdivided in other places in the NEC. . Right from the beginning of 490 [490.21(A)(1)(a)], you see wording that shows that the primary application of over 600v is industrial. . For this reason, I find it easier and more compatible with the rest of the code, to call over 600v as "industrial" equipment voltage rather than "high voltage".
328.2 def + 328.10 lays out the middle ground of these "industrial" equipment voltages by designating 2001-35,000 as medium voltage, or as I would say medium industrial. . T310.5 is an example of a code article that applies only to standard, low industrial, + medium industrial equipment voltages. . 310.6 + 310.7 are 2 examples of code articles that apply only to medium + high industrial equipment voltages.
450.21(C) is an example of a code rule applying to high industrial equipment voltage.
Of course, there are exceptions [such as T300.50], but these breaking points between voltages holds for most equipment addressed in the NEC.
SYSTEMS
0-49 . . Low Distribution
50-1000 . . Medium Distribution
1000-4160 . . High Distribution
4160 & up . . Transmission
0-49 . . Low Distribution is covered by 250.20(A)
50-1000 . . Medium Distribution is covered by 250.20(B)
1000-4160 . . High Distribution and 4160 & up . . Transmission are covered by 250.20(C).
4160v is presented in many text books as the breaking point between distribution and transmission [such as Rockis + Mazur Electrical Motor Controls page 288]. . Industrial plants that are supplied by voltages of greater than 4160v to ground are considered as recieving transmission voltage service.
Certainly there are other ways of categorizing voltages. . And I don't know how you could call one way right and another way wrong. . But I'm teaching electrical apprentices and use of the NEC is critical. . I prefer categories that highlight the breaks found in the NEC.
Looking at it this way, you would understand 250.180 as recognizing 1000v as being a break because it's looking at a system category. . It states this limit as a bottom limit for "high voltage". . You would also understand the bottom limit of 600v "high voltage" in 490.2, 230.200, 240.100, + other places as being a break because it's looking at an equipment category.
Whatever limits/categories you choose, make sure that they are useful in categorizing the information that you use everyday.
High Voltage Connection
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What is High Voltage?
HIGH VOLTAGE CONNECTION DEFINITION:
There is no universally accepted definition, although some industry standards do specify various minimum voltages, above which is considered high voltage. These definitions are generally based on safety considerations or the voltage where arcing will occur. It would be convenient if high voltage was universally accepted to start at a nice round number, for example, 1kV. Instead, we've seen voltages as low as 5V referred to as high voltage. In contrast, according to the Bonneville Power Administration, to be considered high voltage, it needs to be 100kV and above! We'd like to define this relative term from a more practical viewpoint instead:
High voltage starts at the point where designers have to consider additional technical issues, and where there are significantly fewer component suppliers to choose from.
Technical Issues: Certainly, for most engineers, high voltage is different voltage. It's no longer engineering-as-usual. Other variables enter into the design and manufacturing processes. You need to take into consideration creepage distance, insulation thickness, corona and geometrical arrangement. It's no longer a good idea to use your finger to see which component is running hot. Components exhibit unexpected behavior, like resistors that change value as a function of applied voltage.
Component Supplier Issues: Designers need to be more careful in vendor selection. That's because there aren't tons of suppliers, and the technology isn't as well known. Thus, there are larger differences in quality and reliability among high voltage manufacturers. For example, if you need a 5V power supply, there are hundreds of companies that will make them. But if you need, say, 100V or 10,000V, there are only a handful. And of that handful, there is only a couple that makes high quality, reliable supplies.
ADDITIONAL DEFINITIONS:
Any voltage greater than 40 volts is generally considered potentially (!) dangerous.
Voltage of 208V and higher.
High voltage is defined by the DOE Electrical Safety Guidelines as over 600 volts.
Generally considered to be a wire or cable with an operating voltage of over 600 volts.
Any electric potential capable of producing breakdown in air at STP, or around 600volts.
A voltage higher than that used for power distribution. The lower limit is usually taken as either 5000V (Bell) or 8700V (National Electrical Safety Code).
10 kV, because that's about where you have to start worrying about corona and it gets harder to find off the shelf components. [Editor’s note: this is a good practical definition, however, other issues besides corona occurs at lower voltages.]
Generally, a wire or cable with an operating voltage of over 25, 000 volts.
An electrical system or cable designed to operate between 46 kV and 230kV.
Descriptive of transmission lines and electrical equipment with voltage levels from 100 kV through 287 kV.
Least useful definition?: Adj. 1. high-voltage - operating on or powered by a high voltage; "a high-voltage generator"
Medium Voltage: Perhaps an alternative way of defining high voltage would be to add a new term, “Medium Voltage.” Then, high voltage could be 1kV and above, and medium voltage would be some lower voltage up to 999V. (Thanks to Paul Oranges of Huettinger who suggested using this term.)
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