What is Medium Voltage?

[Fchild]

I know that I always concidered anything over 600VAC up to 35KVac as Medium Voltage. Where is this definision? Is there a standard or is this just a ball park description that depends on the person and situation?

 

[dinkelja]

The NEC classifies low voltage as ranging "up to 600 volts nominal", with higher levels being "above 600 volts nominal". No mention of AC or DC I believe. ANSI low voltage range voltage class stops at 600V also. However I generally consider:
Low voltage: 0 to 1000 V
Medium Voltage: 1001 to 72,500V
High: 72.5kV to 242kV
Extra-high voltage above 242kV
Other opinions?

 

[ScottyUK]

The opinion of National Grid Company is that: LV is <250V; MV is 250V - 650V; HV is >650V.

This is quite different to the published regulations which define LV as < 1000V AC or 1500V DC, and HV is >1000V AC or 1500V DC. 'MV' is not longer an officially recognised term over in the UK, although it is frequently used to denote distribution system voltages from 3.3kV up to 66kV as distinct from transmission voltages from 132kV up to 400kV.


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Sometimes I only open my mouth to swap feet...

 

[Fchild]

Thanks for the opinions. I would like to know where in the NEC it discusses this if anyone knows.

 

[davidbeach]

The NEC has one dividing line at 600V although conductors seem to have a divide at 2000V. IEEE/ANSI standards are:
LV-MV divide at 1000V
MV-HV divide at 63kV
HV-EHV divide at 230kV
EHV-UHV divide at 345kV.

That's from memory and a few of the dividing lines may be off by a small amount, but I know the 1000V line is correct.

 

[scottf]

In the US, medium-voltage is normally though of as distribution voltages, which would normally top out at 34.5 kV class (although there is some 46 kV distribution).

46kV and up would be high voltage, i.e. transmission voltage levels. (46 kV and 69 kV are sometimes called sub-transmission voltages)

 

[dpc]

I don't think the NEC has a real definition other than for cable. For cables, NEC defines at 2000 V as David said. A lot of rules change above 600 V.

IEEE definition of 1000V is most common usage I'm aware of.

 

[oldfieldguy]

The electrical power utility I used to work for did it thusly, if I remember correctly:

2300- 13,800: Low voltage
20,000 - 69,000: Medium voltage
138 - 230 kV: High voltage
500 kV: Extra high voltage.

Many of the local industries make the divide their in-plant systems thusly:

<600 volts: Low voltage
2300 - 4160: medium voltage
13,200, 13,800: high voltage

Most of the local heavy commercials define it as:
<300: Low voltage (120, 208, 240, 277)
480: High voltage
>480: call a contractor


old field guy

 

[Zogzog]

IEEE (Red book) for equipment is :

LV 0-600V
MV 601-69kV
HV - 69,001V - 230 kV
EHV - 230,001 - 800kV
UHV ->800kV

NEC states:
LV 0-600V
HV - >600V

 

[Kiribanda]

Fchild,

It sounds like you are from ANSI world.

As per ANSI C84.1,system nominal voltage classes are as follows.

Low voltage : Nominal voltage 1000 Volts or less
Medium voltage : Nominal voltage greater than 1000 and less than 100,000 Volts
High voltage : Nominal voltage equal or greater than 100,000 V and equal or less than 230,000 V
Extra High voltage : Nominal voltage greater than 230,000 Volts

Hope this hepls

Kiri

 

[ters]

In Canada, regardless what the definitions say, it seems that most engineers consider that the upper limit of medium voltage equipment category corresponds with the (wide) availability of standardized pad mounted metal enclosed switchgear and substations. In North America, the highest such standard voltage happens to be 34.5 kV (equipment frequently being rated to 38 kV).

I was recently researching availability of pad mounted metal enclosed substations for 44 kV and concluded that a completive business for such equipment simply doesn’t exists out there. Just very few companies seem to be in the business of custom making metal englosed switchgear or transformers of that voltage rating (44 - 46 kV).

 

[rbulsara]

What Zogzog said.

Kirbanda's info may be more upto date but it does not change really what zogzog said. Highest voltage in use under 100kV is 69kV class (66-69kv) and lowest above 100kV is 115kV (in ANSI world) or 132 kV in IEC world. Same for 1000V limit for LV, highest voltage used below 1000V is really 600V.

I am sure some will prove me wrong by stating a weird voltage system existing somewhere but that would be an exception.

 

[SteveHuck]

I believe the IEEE defines MV as 2001V - 69,000V