Extra-low Voltage – ELV

Extra-low Voltage

Extra-low voltage ( ELV ) is an electrical voltage that poses a low risk of electric shock. According to the International Electrotechnical Commission (IEC) and the UK IET (BS 7671:2008) extra-low voltage means voltage of 50V or less (AC RMS), or 120V or less (ripple-free DC). But there are various standards that define extra-low voltage. The human can touch the live conductor and which do not harm. But under wet condition, the human can experience a mild shock.

Classification of Voltage Levels

The electric power can be generated, transmitted and utilized in different voltages. We must note that different definitions are used in electric power transmission and distribution, compared with electronics design. In addition, different voltages and different grid frequencies are used in the world. In the United States, the National Electrical Code (NEC) and the National Electrical Manufacturer’s Association (NEMA) have guidelines and standards that cover all voltage classifications. The American National Standards Institute (ANSI) oversees the creation, promulgation, and use of thousands of guidelines and standards that affect businesses.

NOTE:This page is for informational use only. Always consult with a certified professional when designing and working on electrical equipment. Never work on energized circuits or perform duties that you are not qualified for.

Classification of Voltage Levels- ANSI

In the United States, the American National Standards Institute (ANSI) establishes nominal voltage ratings for 60 Hz electric power systems over 100 V. Specifically, ANSI C84.1-2020 defines:

• low voltage as 240 to 600 V
• medium voltage as 2.4 to 69kV
• high voltage as 115 kV to 230 kV, 
• extra-high voltage as 345 kV to 765 kV, 
• and ultra-high voltage as 1,100 kV.

Classification of Voltage Levels – BS 7671

British Standard BS 7671:2008 defines high voltage as any voltage difference between conductors that is higher than 1000 VAC or 1500 V ripple-free DC, or any voltage difference between a conductor and Earth that is higher than 600 VAC or 900 V ripple-free DC.

Classification of Voltage Levels- IEC

In the context of building wiring and the general use of an electrical apparatus, the International Electrotechnical Commission defines:

• high voltage as more than 1,000 volts (V) of alternating current (AC) and above 1,500 V of direct current (DC). 
• low voltage as voltage between 50 – 1,000 volts of alternating current and between 120 – 1,500 V of direct current.
• extra-low voltage as lower than 50 V of alternating current and 120 V of direct current

Typical voltages

To help compare different orders of magnitude, the following list describes typical voltage levels.

• 1.5V (DC) – A common open circuit voltage for non-rechargeable alkaline batteries (e.g. AAA, AA, and C cells). 
• 3.8V (DC) – Almost all smartphone batteries work at 3.8 volts. In order to make current flow from the charger to the battery, there must be a potential difference. Therefore battery chargers or USBs for almost all smartphones provide a voltage of 5V.
• 12V (DC) – A common voltage for automobile batteries is 12 volts (DC).
• 110 – 120V (AC) – The most common electrical outlet in any home. The American continent uses a voltage of 110 to 120 volts (AC) while Europe, Asia, and Africa use 220 to 240 volts (AC). 
• 3kV – Voltage required to generate every 1mm of an electric arc. Air is a very bad conductor of electricity and has high dielectric strength. The dielectric strength of air is nearly 3000V/mm.
• 110kV – The voltage in electric power transmission lines used to distribute electricity from power stations can be several hundred times greater than consumer voltages, typically 110 to >500 kV (AC).
• 300 MV – A typical lightning flash is about 300 million Volts and about 30,000 Amps.