Learning voltage level is necessary when talking about power grid distribution or power system transmission. We need to differ each voltage level in order to decide how we handle them. Below is the list of voltage levels, their explanation comes later.
- Rated voltage
- Nominal voltage
- Extra low voltage
- Low voltage
- Medium voltage
- High voltage
- Extra high voltage
Rated voltage is the maximum voltage at which the device can be operated safely. If we increase the voltage further, the device may break or not function properly. Simpler to say, rated voltage is the maximum voltage limit of a device.
Rated voltage is not only presented by a number, we will find its tolerance rate. This number uses percentage to show the minimum and maximum range of the rated voltage. For example if a device has 50V as rated voltage and 10% as its tolerance, the minimum voltage will be 45V and the maximum voltage will be 55V.
This 45V indicates that this device won’t work properly if the voltage is less than 45V. The 55V indicates that this device will be damaged or failed to operate if the voltage is more than 55V. This device must be supplied with voltage between 45V and 55V, no less and no more.
Nominal means ‘named’. Nominal voltage is how we name a voltage source into a category. This number indicates the output of a voltage source. But remember that the output doesn’t have to be exactly the same as written. For example, a 12V battery will produce voltage around 12V, it can be any voltage around 12V.
This nominal voltage is often found in electrical power systems; they are named according to their voltage output. A power system with nominal voltage 10kV will have voltage near and around 10kV. Nominal voltage can be found in every electrical system. There are some most used nominal voltages: 440 V, 690 V, 3.3 kV, 6.6 kV, 11kV, 33 kV, 66 kV, 132 kV, 220 kV, 400 kV, and 765 kV.
Extra Low Voltage Level
Extra low voltage or ELV is the part of low voltage level range. This is the lowest voltage level we will encounter. From its name implies, this voltage range does not have up to low risk of electrical shock. Even though this voltage range is only at low risk of shock, there are different standards for every voltage level including extra low voltage (ELV).
Observe the standards below about extra low voltage:
- EU Standard EN 61140 = voltage level less than 50V AC or 120V DC (no ripple).
- General Product Safety Directive (2001/95/EC) = electrical equipment with voltage below 50V AC or 75V DC.
IEC (International Electrotechnical Commission)
- IEC 61140:2016, Basic Safety Publication = voltage less than 50V AC (rms) or 120V DC (no ripple).
- IEC 60364-4-41:2017, Group Safety Publication = voltage less than 50V AC (rms) or 120V DC (no ripple).
Australia and New Zealand
- AS/NZS 3000 = voltage less than 50V AC and 120V DC (no ripple)
- AS/ACIF S009 Clause 188.8.131.52 Extra-Low Voltage (ELV) = voltage level less than 42.4V peak or 60V DC (AS/NZS 60950.1:2003).
Regulatory Standard no.10, Brazilian Ministry of Labor and Employment = voltage less than 50V AC or 120V DC.
Low Voltage Level
Low voltage level has higher risk than the ELV even though it is still considered as a low voltage. We can’t touch the live low voltage wire bare-handed because it will give dangerous shocks and worse when it is wet.
IEC (International Electrotechnical Commission)
- IEC 61140:2016 = low voltage ranges from 0 to 1000V AC (rms) or 0 to 1500V DC.
- IEC 60038, IEC Standard Voltages = low voltage supply system ranges from 50 to 1000V AC or 120 to 1500V DC
British Standard, BS 7671, Requirements for Electrical Installations. IET Wiring Regulations = low voltage supply system ranges from 50 to 1000 V AC or 120 to 1500V DC between conductors, or 600V AC or 900V DC between conductors and earth.
United States National Electrical Code (NEC)
- NEC, NFPA 70, article 725 (2005) = the low distribution system voltage (LDSV) ranges from 0 to 49V.
- NFPA standard 70E article 130, 2021 = energized electrical conductors and circuit parts = less than 50V from safety operation requirement of electrical hazards.
- UL standard 508A article 43 (table 43.1) = 0 to 20V peak with 5A or 20.1 to 42.4V peak with 100VA as low voltage circuit.
Medium Voltage Level
United States – American National Standard Institute (ANSI)
- ANSI C84.1 = medium voltage ranges from 1000V to 100kV.
- IEEE 141, Red Book = put the ANSI C84.1 as the MV voltage reference, from 1000V to 100kV.
- NEC voltage standards = medium voltage distribution ranges from 50 to 1000V
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High Voltage Level
High voltage can possibly produce spark in the air and poses a high risk of electrical shock by contact or proximity.
International Electrotechnical Commission
- IEC along with its national partners (IET, IEEE, VDE, etc) = high voltage ranges above 1000V AC or 1500V DC.
National Electrical Manufacturers Association (NEMA) = high voltage ranges from 100V to 230kV.
British Standard BS 7671:2008 = high voltage level between conductors above 1000V AC or 1500V DC (no ripple); or voltage between conductor and ground above 600V AC or 900V DC (no ripple).
Extra High Voltage Level
Extra High Voltage (EHV) depends on where we find or use it.
- Electric power transmission, extra high voltage ranges between 345kV to 765kV.
- Power supply for electronics (EHV power supply) = voltage above 275kV.