Low, Medium & High Voltage Definition

[spark2]

I'm looking for a qualified definition for Voltage levels ie. Low Voltage < ? Medium Voltage > to < & High Voltage > ? There are various deinitions for these in the NEC & NFPA - Is there a definitive answer for construction, maintenance & utility electricians? Is there a standard and if not why not?

 

[charlie b]

I think not. The "why not" is that it means different things to different sectors of the industry. In my world, "LV" is below 120 VAC, and applies to fire alarm, security, and similar systems. I use "MV" for anything above 480 VAC, up to 25,000 VAC or so, and "HV" for anything higher. But a person who works with fire alarm systems might consider 120 VAC to be "high voltage." So whenever I hear or read someone's use of these terms, I make sure to verify what that person means by the terms, before proceeding.

 

[480sparky]

FWIW, in my 1925 NEC, Low Voltage is 600 volts or less.

High Voltage is 601-5000 volts.

Extra-high voltage is over 5000 volts.

But, that was 83 years ago.....

 

[zog]

Although many use these terms incorrectly, because it seems to be all relitive to what you are used to, they are defined by IEEE for equipment desginations as"

LV - 600V or less
MV 601V-69,000V ( Changed a few years ago)
HV - 69,001V-230,000V
EHV 230,001V-800,000V
UHV >800,000

I feveryone used these properly alot of confusion could be avoided. I get alot of calls for service work and repairs on "High voltage" breakers, when asked if we work on HV breakers my answer is always, some of them, but only up to 115kV, the answer is usually, "I was talking about 4160V" or something like that.

 

[weressl]

I'm looking for a qualified definition for Voltage levels ie. Low Voltage < ? Medium Voltage > to < & High Voltage > ? There are various deinitions for these in the NEC & NFPA - Is there a definitive answer for construction, maintenance & utility electricians? Is there a standard and if not why not?

See attached IEEE-141-1993 Table 3-3

 

[spark2]

Thanks for your input !

 

[iwire]

I notice they don't list any voltage under 120 volts.

Apparently 24 VAC is 'no voltage'.

 

[dnem]

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.

 

[zog]

Huh??? no way is 4160V at all associated with "Transmission".

 

[dnem]

Huh??? no way is 4160V at all associated with "Transmission".

Not associated with substation to substation transmission, I agree. . 4160v from substation to pole mounted kettle transformer is very common in my area. . But much more important is that it is listed as the breaking point between what is considered distribution and what is considered transmission levels in text books.

 

[zog]

Sorry i have to disagree with you and this is exactly what I was refering to as using terms that are relative to what you do being misleading. Both Laszlo and I posted the IEEE definitions of the voltage clases the OP asked about, lets not muddy the waters and say it is relative to what you do.

What you desribed is not a transmission system by any authoritys definition, it is distribution.

 

[dnem]

Sorry i have to disagree with you and this is exactly what I was refering to as using terms that are relative to what you do being misleading. Both Laszlo and I posted the IEEE definitions of the voltage clases the OP asked about, lets not muddy the waters and say it is relative to what you do.

What you desribed is not a transmission system by any authoritys definition, it is distribution.

"lets not muddy the waters and say it is relative to what you do"
OK so now you have your IEEE voltage category limits. . What are you going to do with them ? . Will they help you understand why 250.180 lists over 1000v as high voltage ? . Will they help you understand why 490.2 lists over 600 as high voltage ? . Will the IEEE category limits help you understand the NEC installation requirements for something that is 700v or maybe 800v ?

I know that 700v equipment is categorized as high voltage and must follow the requirements of Article490. . I know that a 700v system is not categorized as high voltage by the NEC and does not have to follow the requirements of Article250 part 10.

Understanding NEC requirements is relative to what I do. . If you bring IEEE voltage categories into an NEC installation answers website, aren't you the one that will "muddy the waters" ?

You seem to think that there is only one answer to the low medium high voltage question. . I know there are many answers and none can claim to be the only right one. . Here on this website, the best answer is the NEC answer.

 

[dnem]

What you desribed is not a transmission system by any authoritys definition, it is distribution.

The break between system transmission and system distribution voltage [4160v] is the only one on my chart that doesn't come from the NEC and therefore can readily be disputed. . I have no way to argue in favor of the text book and I won't try to. . I'll use a diffferent voltage level breaking point if I can find one.

 

[zog]

You seem to think that there is only one answer to the low medium high voltage question. . I know there are many answers and none can claim to be the only right one. . Here on this website, the best answer is the NEC answer.

Did you even read the OP?

"I'm looking for a qualified definition for Voltage levels ie. Low Voltage < ? Medium Voltage > to < & High Voltage > ? There are various deinitions for these in the NEC & NFPA - Is there a definitive answer for construction, maintenance & utility electricians? Is there a standard and if not why not?"

Is there a standard for maint and utility electricians, the answer is [/b] YES, the IEEE [/b] definitions posted by 2 people in this forum that are thinking outside the NEC as the OP asked.

 

[dnem]

I think I see a good solution to the conflict between the NEC and IEEE.

Start with dropping the text book mention of 4160v because none of these text books are an authority nor do they provide practical help in answering the question of voltage.

The NEC covers everything under 90.2(A) and offers the following categories:

EQUIPMENT
0-600 . . Standard
601-2000 . . Low Industrial
2001-35,000 . . Medium Industrial
35,001 & up . . High Industrial

SYSTEMS
0-49 . . Low Distribution
50-1000 . . Medium Distribution
1000 & up . . High Distribution

When we get into 90.2(B) [which repeatedly refers to utilities], IEEE categories would be useful.

TRANSMISSION
0-600 . . Low
601-69,000 . . Medium
69,001-230,000 . . High
230,001-800,000 . . Extra High
800,000 & up . . Ultra High

Pick from among the 3 applicable lists depending on the specific application that might arise.

 

[dnem]

Did you even read the OP?

Yes, did you ?

"I'm looking for a qualified definition for Voltage levels ie. Low Voltage < ? Medium Voltage > to < & High Voltage > ? There are various deinitions for these in the NEC & NFPA - Is there a definitive answer for construction, maintenance & utility electricians? Is there a standard and if not why not?"

Is there a standard for maint and utility electricians, the answer is [/b] YES, the IEEE [/b] definitions posted by 2 people in this forum that are thinking outside the NEC as the OP asked.

"construction, maintenance & utility electricians"
The standard for construction, maintenance & utility electricians is different but you're too busy telling everybody that you have all of the answers to stop and listen to anybody else.

Construction and maintenance is the NEC
Utility might very well be IEEE, I don't know that for sure

What I do know is that a construction or maintenance electrician needs to understand NEC categories above all else. . Thinking outside of the NEC isn't of much value for construction and maintenance.

There is no one right answer to this question.

Stop being so sure of yourself and be willing to listen to logic.

 

[zog]

Yes, did you ?

Yep, the difference is I answered it

What I do know is that a construction or maintenance electrician needs to understand NEC categories above all else. . Thinking outside of the NEC isn't of much value for construction and maintenance.

only is those systems are covered by the NEC

Stop being so sure of yourself and be willing to listen to logic.

Ditto

 

[charlie]

What is the problem?

What is the problem?

These are the ones that I have always used and they match the IEEE voltages except for the ultra-high voltage.

LV = Voltage levels that are less than or equal to 1 kV

MV = Voltage levels that are greater than 1 kV, but less than or equal to 69 kV

HV = Voltage levels that are greater than 69 kV, but less than or equal to 230 kV

EHV = Voltage levels that are greater than 230 kV, but less than or equal to 800 kV

UHV = Voltage levels that are greater than 800 kV

I am having a problem with the reason this is such a great consternation since you would use the scale of the code you are working with. The IEEE scale would fit with the NESC since the IEEE publishes the NESC. Use the scale that the NEC uses when using the NEC.

 

[iwire]

I am having a problem with the reason this is such a great consternation since you would use the scale of the code you are working with. The IEEE scale would fit with the NESC since the IEEE publishes the NESC. Use the scale that the NEC uses when using the NEC.

It should be that easy but egos get in the way.:grin:

 

[zog]

It is that easy, if you read the OP's question.