Low, Medium & High Voltage: Definitions and Ranges
Sep 15, 2026
Low voltage (LV), medium voltage (MV), and high voltage (HV) are industry terms for grouping electrical systems by nominal voltage. There is no single global table that everyone uses-the boundaries depend on which standard, which country, and whether you mean system voltage or equipment rating.
Always state the nominal voltage in kV (e.g., 11 kV, 33 kV, 132 kV) instead of relying on vague labels alone.
Why definitions differ
| Context | What changes |
|---|---|
|
Geography |
IEC (international/Europe) vs ANSI/NEMA (North America) |
|
Standard |
IEC 60038 (voltage levels) vs IEC 62271 (switchgear) vs NEMA C84.1 (system classes) |
|
Discipline |
Power utility vs industrial plant vs building electrical (NEC) |
|
Equipment vs system |
A 415 V motor is LV; a 400 kV transmission line is EHV |
A control engineer may call 50 V "high voltage." A utility lineman may reserve "high voltage" for 69 kV and above. Both can be correct in their field.
IEC definitions (IEC 60038)
IEC 60038 defines standard voltage levels for power systems:
Low voltage (LV)
Nominal voltage up to 1,000 V AC or up to 1,500 V DC
Common LV nominal voltages:
230/400 V (Europe, three-phase)
120/208 V, 120/240 V (North America)
690 V (industrial motors)
Used for: final distribution, commercial buildings, industrial panels, motor control.
High voltage (HV) - IEC general sense
Voltage levels in excess of low voltage
IEC does not formally define "medium voltage" in 60038-but MV is universally used in industry as a subdivision of the HV domain.
Medium voltage (MV) - industry practice (IEC 62271-1)
IEC 62271-1 (high-voltage switchgear) notes:
Equipment with rated voltage above 1,000 V is high-voltage switchgear. The term medium voltage is commonly used for distribution systems above 1 kV and generally up to and including 52 kV.
Typical MV nominal voltages:
| Voltage | Common use |
|---|---|
|
3.3 kV, 6.6 kV |
Industrial plants, mining |
|
11 kV, 13.8 kV, 15 kV |
Urban/suburban distribution |
|
20 kV, 22 kV, 33 kV |
Primary distribution feeders |
|
45 kV, 52 kV |
Upper MV range, large substations |
Used for: primary distribution, large industrial substations, underground cables, ring main units.
Extra-high voltage (EHV) and ultra-high voltage (UHV)
Above MV, transmission uses higher classes (terminology varies by region):
| Class | Typical range | Application |
|---|---|---|
|
HV (transmission) |
66 kV – 230 kV |
Regional transmission |
|
EHV |
230 kV – 765 kV |
Bulk power transmission |
|
UHV |
≥ 1,000 kV AC |
Long-distance bulk transfer (China, India, etc.) |
Common transmission voltages: 66 kV, 110 kV, 132 kV, 220 kV, 400 kV, 500 kV, 765 kV, 1,000 kV.
North American definitions (ANSI/NEMA C84.1)
Referenced by NEC Article 100, NEMA C84.1 defines system voltage classes:
| Class | Nominal system voltage |
|---|---|
|
Low Voltage (LV) |
1,000 V or less |
|
Medium Voltage (MV) |
Greater than 1 kV and less than 100 kV |
|
High Voltage (HV) |
100 kV to 230 kV |
|
Extra-High Voltage (EHV) |
Greater than 230 kV and less than 1,000 kV |
|
Ultra-High Voltage (UHV) |
1,000 kV or greater |
Note: Under C84.1, 15 kV and 35 kV distribution are medium voltage-not "high voltage" as a lineman might say.
Side-by-side: IEC vs ANSI
| Term | IEC (common practice) | ANSI/NEMA C84.1 |
|---|---|---|
|
Low voltage (LV) |
≤ 1 kV AC / ≤ 1.5 kV DC |
≤ 1 kV |
|
Medium voltage (MV) |
> 1 kV, typically ≤ 35–52 kV |
> 1 kV and < 100 kV |
|
High voltage (HV) |
> 1 kV (equipment); transmission context higher |
100 kV – 230 kV |
|
EHV |
Varies |
230 kV – 1,000 kV |
|
UHV |
≥ 800 kV – 1,000 kV+ |
≥ 1,000 kV |
Other voltage categories you may hear
| Term | Typical range | Standard / use |
|---|---|---|
|
Extra-low voltage (ELV) |
≤ 50 V AC / ≤ 120 V DC |
IEC 61140 - safety extra-low voltage (SELV) |
|
Low voltage (building) |
≤ 1,000 V |
NEC - most chapters split at 1,000 V |
|
Control voltage |
24 V, 48 V, 110 V DC |
Not power-system MV/HV - instrumentation |
What voltage class means for equipment and testing
Voltage class determines equipment design, clearances, test methods, and safety rules:
| Voltage class | Typical equipment | Test implications |
|---|---|---|
|
LV |
MCC, LV switchgear, transformers ≤ 1 kV |
IR test 500 V–1 kV; BDV on oil optional |
|
MV |
MV switchgear, cables, transformers 11–33 kV |
IR 2.5–5 kV; VLF on cables; SF6 GIS |
|
HV/EHV |
Transmission breakers, large power transformers |
5–10 kV+ IR; tan delta; PD monitoring; specialized hipot |
Huazheng test equipment spans these classes-from LV megohmmeters and transformer loss testers to 5 kV–15 kV IR testers, VLF hipot systems, and SF6 analyzers for MV/HV substations.
Common nominal voltages worldwide
| Region | LV | MV (distribution) | HV (transmission) |
|---|---|---|---|
|
Europe / IEC |
400 V |
10 kV, 20 kV, 30 kV |
110 kV, 220 kV, 380 kV |
|
UK |
400 V |
11 kV, 33 kV |
132 kV, 275 kV, 400 kV |
|
North America |
480 V, 600 V |
4.16 kV, 12.47 kV, 13.8 kV, 34.5 kV |
69 kV, 115 kV, 138 kV, 230 kV, 345 kV, 500 kV |
|
China / Asia |
380 V |
10 kV, 35 kV |
110 kV, 220 kV, 500 kV, 1,000 kV UHV |
Always confirm line-to-line vs line-to-ground nominal when comparing international systems.
Practical rules for engineers and buyers
Name the kV - say "11 kV distribution" instead of only "medium voltage."
Cite the standard - "MV per IEC 62271-1" or "MV per NEMA C84.1."
Distinguish equipment rating from system class - a 33 kV-rated cable on an 11 kV system is still MV equipment.
Match test equipment to voltage class - megger voltage, VLF level, and hipot rating must align with asset rating.
Safety training differs by class - MV and HV work require different qualifications, PPE, and clearance rules.
