Voltage Levels – Confused?

By Steven McFadyen on March 23rd, 2009

I was having a conversation the other day about voltage levels. While everyone was in agreement that low voltage was 1000 V and less, there was more confusion on the terms 'Medium Voltage' and 'High Voltage'.

Our attempt to resolve this was to look at IEC60038 "Standard Voltages", 20002. This didn't help in that the standard does not define the terms 'Low Voltage', 'Medium Voltage', etc. However, what the standard does do is group voltages into bands and this is useful.

IEC 60038 Standard

The standard defines the following bands:

band 1 - A.C. systems 100 V to 1000 V
band 2 - A.C and D.C traction systems
band 3 - A.C. systems above 1 kV to 35 kV
band 4 - A.C. systems above 35 kV to 230 kV
band 5 - A.C. systems above 245 kV

A.C. systems 100 V to 1000 V

50 Hz three phase systems 230/400, 400/690 and 1000 V
60 Hz three phase systems 120/208, 240, 277/480, 480, 347/600 and 600 V
60 Hz Single phase three wire systems 120/240 V

Supply voltage range ±10 % at the supply terminals
Supply terminal to final equipment maximum 4% voltage drop

A.C and D.C traction systems

D.C. systems 600, 750, 1500, 3000 V
A.C. systems 6250, 15000, 25000 V

600 V and 6250 V are non preferred and should not be used if possible

A.C. systems above 1 kV to 35 kV

50 Hz systems - a) 3.3, 6.6, 11, 22, 33 kV
50 Hz systems - b) 3, 6, 10, 15, 20, 35 kV
60 Hz systems - c) 4.16, 12.47, 13.2, 13.8, 24.94, 34.5 kV

It is recommended that either (a) or (b) be used, not both

A.C. systems above 35 kV to 230 kV

Series I - 45, 66, 110, 132, 150, 220 kV
Series II - 69, 115, 138, 230 kV

Only one series should be used in each country

A.C. systems above 245 kV

Not being an expert on higher voltages the table was a little confusing to me, so I'm not going to try and summarise it.

Back to the problem

The standard didn't answer the original question, but it did provide useful background. I would now be tempted to classify 'Low Voltage' as less than 1 kV, 'Medium Voltage' as above 1 kV to 35 kV and 'High Voltage' as 35 kV to 230 kV (with ultra high or extra high above 230 kV). Feedback, comments or further insight into this is welcome.

Related Links

Railway Electrification Voltages

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Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

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View 3 Comments (old system)

ManjoloPhiri says:

9/1/2011 2:11 PM

The terms "High Voltage"," Medium Voltage", "Low voltage" are relative terms. Which means you are free to define them according to where you are working. Forexample where I work we have different voltages: 220V, 400V, 550V, 3.3 kV, 11 kV and 33 kV. So we have defined high voltage as anything above 650V, Medium voltage is above 240V up to 650V, low voltage is anything 240V and below. This is working for us.
- Steven says:
  
  9/1/2011 2:11 PM
  
  Electropedia has the following definition for medium voltage: medium voltage (abbreviation: MV) (not used in the UK in this sense, nor in Australia) any set of voltage levels lying between low and high voltage NOTE – The boundaries between medium and high voltage levels overlap and depend on local circumstances and history or common usage. Nevertheless the band 30 kV to 100 kV frequently contains the accepted boundary.
Rhys Jones says:

9/26/2012 3:25 PM

Steven

I tend to take a steer from manufacturers; where it appears (as you have suggested) up to (an including) 1kV=LV; above 1kV upto 35/38kV=MV greater would be HV.

If you look at Schneider, ABB, FKI, Eaton, Siemens et al, this seems to be the common levels for designating voltages against Low/Medium/High.

For higher voltages, there seems to be some discussion as to whether HV or HT should be applied, but then I wouldn't feel qualified to work on anything above 33kV.

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