Commonly used AC voltage levels

AC voltage levels:

0.316V The most common nominal level for consumer audio equipment is -10 dBV, 0.316 volts root mean square (VRMS).

0.7746V The reference voltage for the decibel unloaded (0 dBu) is the voltage required to produce 1 mW of power across a 600 ohms load (approximately 0.7746 VRMS)

1V  The reference voltage for the decibel volt (0 dBV) is 1 VRMS, which is the voltage required to produce 1 milliwatt of power across a 1 kilo-ohm load

1.228V The most common nominal level for professional equipment is 4 dBu. A signal at +4 dBu is equivalent to a sine wave signal with a peak amplitude of approximately 1.737 volts,or any general signal at approximately 1.228 VRMS.

12V A low voltage lighting system usually operates on 12 or 24 volts.

24V A low voltage lighting system usually operates on 12 or 24 volts.

24V Used for controlling relay coils in some automation and control systems.

50V Extra-low voltage high limit is 50V AC


50V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500V DC

75V Typical telephone line ring voltage is 75 V a.c.(20 or 25 Hz), it could be between 40 and 150 Volts (15-68 Hz)

100V Mains voltage in Japan. Reference voltage level used on electrical power stations measurements (100V = nominal high voltage on line being measured)

110V Mains power in USA, the voltage you expect to get from mains outlet
115V Mains power in USA, the voltage you expect to get from mains outlet
120V Mains power in USA, the output voltage on the distribution transformer

200V If the voltage is less than 200 V, then the human skin is the main contributor to the impedance of the body in the case of a macroshock—the passing of current between two contact points on the skin.

208V The voltage you expect to get between two phases in USA in case our apartment
gets two phase wires from three phase transformer (208/120V)

220V Old European nominal voltage, harmonized to 230V

230V Electricity supplies within the European Union are now nominally 230 V ± 6% at 50 Hz

240V the voltage you expect get between two hots in USA on your hous
240V Old nominal mails voltage used in UK, harmonized to 230V
240V the voltage you get between two hots in USA on the distribution transformer

277V Voltage between phase and neutral on 277/480V three phase system, used in USA for example lighting loads on big buildings

380V Voltage between phases on 220/380V three phase system (old European system)

400V Voltage between phases on 230/400V three phase system (modern European system)

415V Voltage between phases on 240/415V three phase system (old UK system)

450V If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs

480V Voltage between phases in USA in commonly used 3 phase distribution

600V Three phase power voltage

690V Three phase power voltage used in industry for larger electrical motors (Europe)


1000V Isolation test voltage for 130V rated working voltage basic isolation (IEC950)

1000V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c
1000V There phase power voltage used on 1 kV power distribution (in use in Finland)

1350V Basic insulation of 1350V rms is needed for test-and-measurement instruments rated at 250V (IEC 61010-1)

1500V Basic insulation of 1500V rms is needed for information-technology products rated at 250V (IEC 60950-1)

1500V Isolation test voltage for 230V rated working voltage (IEC950) (basic isolation)

2100V Isolation test rating for reinforced isolation for 130V rated devices

2300V Use 2300V rms or 3250V dc test voltage for dielectric-withstand test for double insulation

7.2kV Common distribution voltage in USA

10kV Common distribution voltage in Finland

11kV Common distribution voltage in UK, New Zealand and Australia

12.47kV Common distribution voltage in USA

20kV Common distribution voltage in Finland

25kV Electrical trains use 25kV 50Hz power in Finland

33kV Common distribution voltage in UK, New Zealand and Australia

34.5kV Common distribution voltage in USA

110kV Commonly used voltage level on long distance electrical transportation lines

220kV Commonly used voltage level on long distance electrical transportation lines

400kV Commonly used voltage level on long distance electrical transportation lines


  1. pompa submersibila says:

    Your blog is so naturally informative

  2. RJL Electrical Ltd. Electrician Ottawa says:

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    [...]Commonly used AC voltage levels « Tomi Engdahl’s ePanorama blog[...]…

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  5. jumpjack says:

    I think there is an error:

    400V Voltage between phases on 220/400V three phase system (old European system)

    415V Voltage between phases on 230/415V three system (modern European system)

    220/380V before
    230/400V now

    • tomi says:

      Thank you for your feedback.
      You found an error in my article, and that for correction.
      I just updated the corrected information to the article:

      380V Voltage between phases on 220/380V three phase system (old European system)

      400V Voltage between phases on 230/400V three phase system (modern European system)

      415V Voltage between phases on 240/415V three phase system (old UK system)

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  7. Carlos says:

    13.8 kV Common distribution voltage in Brazil

    • Tomi Engdahl says:

      Thank you for addition.

      I was slightly wondering where does this specific voltage come from and I have a theory.

      In Europe (50 Hz power) we have on three phase power voltage is typically 400V and medium voltage of 10kV or 11 kV (sometimes 20 kV but that’d different story).

      In USA (60Hz) the three phase power is typically 480V, which is actually 20% higher than in Europe just like the frequency.
      For example many transformers and motors designed 400V 50Hz can work acceptably at 480V 60 Hz (or is pretty trivial to design one that does both).

      That 13.8 kV is around 20% higher than 11 kV… And Brazil is 60 Hz country.

  8. Tomi Engdahl says:

    AC/DC Power Supplies: Four Questions to Ask

    1. Can you connect the power supplies in parallel to provide higher output power or configure them to provide multi-phase or split phase outputs?

    2. What voltages and currents can I expect from modern power supplies?

    Voltage ranges have increased, particularly in military/avionics applications. Examples include:

    Standard avionics power plant simulation, which currently runs from 360 Hz to about 800 Hz.
    Simulation of next-generation avionics power plants already requires 1200 Hz and that will increase. Power at these frequencies is needed to test the electronics that will connected to those power plants.
    Torpedo alternator simulation, 3 kHz-4kHz, is needed to test the downstream power converters and electronics that will be connected to those alternators.

    Instead of the traditional 150 and 300 VAC ranges, the latest generation of AC/DC supplies now produce voltage ranges of 200 and 400 VAC, as well as DC voltages of 250 VDC and 500 VDC. These higher DC voltages come in handy in many applications. For example, MIL-STD-704, Test Method HDC302 requires voltage transients up to 475 VDC.

    3. I need to test my equipment at multiple ranges. What do I need?

    4. What features should I look for?
    Many of today’s AC/DC power sources have features that make testing easier and more effective. These include touchscreen displays dashboards and control panels where you can save your GPIB address or set your RS-232 parameters, or set up your LAN connection.

  9. Jon says:


    12v – car battery

    16volt – door bells

    24v – PLC controls, Boiler Controls

    110v- single phase – PLC Controls

    120/240volt – single phase residential power, Lighting Panel in Commercial and Industrial

    120/208volt- Single phase taken from 3 phase in small commercial apps

    120/208volt- three phase small commercial apps or Lighting Panel in Commercial and Industrial

    240volt three phase – three phase old industrial sites (generally no neutral, etc delta) sometimes wild

    240/480volt – single phase – not used much anymore

    240/416volt- three phase very old commercial, or what we connect to euro equipment, while still supplying 60hz

    277/480- three phase old larger commercial apps

    480volts three phase (generally no true neutral, could have high resistance grounding) -older industrial, and oilfield sites

    347/600volt -three phase large commercial, schools, and hospitals

    600 volt – three phase (generally no neutral, could be high resistance grounding) new larger industrial, some Oilfield

    2300v- three phase larger motors

    4160volt – three phase big industrial, larger motors

    2300/4160 three phase, big industrial, and oilfield

    7.2kv – single phase voltage REA overhead lines

    13.8kv – three phase Generator stations, at big industrial sites, Oilfield, and Power Company

    14.4kv- single phase – residential underground to pad transformers, on Earth Return neutral overhead power poles

    14.4/25kv- three phase , big industrial sites, some Oilfield, Power Company Grid on Distribution side of subs

    69kv- three phase transmission (substations)

    132kv three phase transmission (to Substations from Generator Stations) usually towers city to town, around larger cites to subs

    230kv- three phase transmission to larger substaions from Generator Stations) usually H frames city to city

    500kvdc – DC Power Big Power, Generation Stations to Big Cities

  10. Tomi Engdahl says:

    Why doesn’t the US use 220V like everyone else in the world?
    Common question about household electrical power supply

    It’s a common question tied to a couple of common misconceptions. First is the idea that the United States is the only country in the world to use the 120V 60Hz standard. The fact of the matter is that there are many other countries that primarily use 120V. To this end, there is no “everyone else in the world”. Some countries use 240V, some 230V, others 220V, and so on.

    To answer the question, though—the US does have a higher power supply. Nearly all homes in the US have 240V alternating current lines at the service entrance to the household as well as select locations within the home. The reason it’s 240V is because that’s the power line that has been standardized over here. Some European countries use 220V, while some specify 230V; most appliances will accept 220-240V however.

    The appliances hooked up to this higher power supply (generally speaking) include more energy dependent machines like ovens and laundry machines. Regular appliances like lamps, laptops, and phones do not need access to this power.

    For those who are surprised to hear households have 240V coming into the home, the way it works is as follows: right prior to the residence entry, the line transformer secondaries are center-trapped so as to provide split-phase 240V on two hot legs (1 and 2) and neutral at the center tap (which is referenced to Earth at the breaker box). For most home outlets, either leg 1 or leg 2 is used with the neutral line to provide 120V alternating current to power small appliances with a plug-in cord.

    For larger appliances, as in the case of the aforementioned oven and laundry machine, they will use leg 1 to leg 2 voltage, which is a straight shot of 240V line to line out of special outlets, or otherwise specially hardwired to specific areas of the home. While larger appliances generally draw approximately 1800 watts (15 amps at 120V), these special outlets / hardwired spots can take up to 7200 W (30A at 240V).

    Now, historically speaking, one of the main reasons why the US stuck with 120V as its standard power supply largely has to do with the fact that it was initially tied to carbon filament lighting. Later, a metal filament was created which could be used for more efficient power distribution systems using 220V, but since the country’s power grid was already largely established using 120V infrastructure, there was no real gain to scrapping the initial system just to go with a new higher-voltage system. So 120V was made the standard.

    The United Kingdom is one area of the world that did change things up after setting up its power grid.

    So, the answer to the question is a nation’s needs come before global unity.

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  13. RJ says:

    i like this. I have some to add to the end. In the USA we have 138 kV, 345 kV, and 765 kV for three phase transmission.

  14. Maciek says:

    3kV Common voltage for large industrial motors (Europe)
    6kV Common voltage for large industrial motors (Europe)
    15kV Common distribution voltage in Poland
    20kV Common distribution voltage in European Union

  15. Tomi Engdahl says:

    The Most Useful Transformer Ever


    In the U.S., 277 VAC has been used in commercial retail and industrial fluorescent lighting for a very long time (45 plus years). These lights could be nearly as efficient using the much more common 240 VAC, but there is a side benefit because thieves won’t steal the lights that use 277 VAC. I don’t know if that is a primary reason for using 277 VAC, but it does help reduce the number of stolen lights.

    Read about 3 phase power. You will learn why 277 VAC 1P is the universal US lighting supply

    A Google search for “277 volt transformer” brings up “120V to 277V step up/down” transformers and dual primary transformers like the one you have.

  16. Tomi Engdahl says:

    A Tale of Two Phases and Tech Inertia

    What kind of power service is in the United States? You probably answered 120-volt service. If you thought a little harder, you might remember that you have some 240-volt outlets and that some industrial service is three phase. There used to be DC service, but that was a long time ago. That’s about it, right? Turns out, no. There are a very few parts of the United States that have two-phase power. In addition, DC didn’t die as quickly as you might think. Why? It all boils down to history and technological inertia.

    You probably have quite a few 120-volt power jacks in sight. It is pretty hard to find a residence or commercial building these days that doesn’t have these outlets. If you have a heavy duty electric appliance, you may have a 240-volt plug, too.

    Industrial customers, on the other hand, are likely to get three-phase service.

    Edison, Tesla, and Westinghouse famously battled between using AC and DC current. Back then, AC didn’t mean three-phase AC, though. Two-phase, where the phases were 90 degrees apart, was an easier system to analyze and generate. The famous generators at Niagara Falls, for example, produced two-phase.

    It was 1918 before mathematical tools for dealing with polyphase AC readily came about. By then, two-phase was pretty well entrenched.

    Big City, Old Power

    This was a similar situation with DC power. Did you know that Con Edison — New York City’s power company — still provided DC to some buildings until late 2007? Even then, the buildings didn’t switch everything to AC. They just installed converters so the DC motors that run infrastructure like the elevators didn’t need replacing. The conversion to AC started in 1928 and was supposed to take 45 years. Like most projects, it ran long and took nearly 80 years.

    In the case of two-phase, though, there are still pockets of it in Philadelphia and Hartford Connecticut.

    You might wonder if the power companies in those two cities actually still maintain two-phase generators. As far as we can tell, no. They just convert from three-phase to two-phase using a Scott-T transformer

    Why 120V? Because Edison’s first generators produced 110V (although, in fairness, 110V DC). After World War II, the nominal voltage kept creeping up until it settled on 120V by 1967. In 1899, a power company in Berlin decided to switch to 220V to increase its ability to distribute power. This took over Europe where 230V (raised up from 220) is the usual voltage.

    Striking Photos of Philadelphia’s Abandoned Power Stations

  17. Tomi Engdahl says:

    Detailed two part documentary on electricity in Japan and how it may affect you as a foreigner …

    Electricity in Japan PT 1

    Electricity in Japan PT 2

  18. Tomi Engdahl says:

    Living in Japan: Electricity – Grounding appliances correctly

    In this video I explain how to correctly ground appliances that need it in Japan, such as computers and UPS units – even in cases when you cannot find a grounded outlet. A common problem!
    I also explain what NOT to do and why – with some simple demonstrations.

  19. Tomi Engdahl says:

    Transformers & Earth Connections

    Earth connections used with isolating transformers and building site transformers. An isolating transformer has no connection to earth at all, although the mains earth connection is often continued through to the outlet socket. A 110V site transformer has the centre of the output winding connected to earth, so that both output conductors are at 55V relative to earth.

    Site transformers can be obtained with RCD protection (generally the much larger ones) but there is usually no point, as 55V is considered to be low enough as to not cause injury. Another issue with RCDs on a construction site would be unwanted tripping due to moisture ingress.

    The larger transformers have MCBs for each output, so a short to earth should trip the MCB. Smaller ones do not, as they are intended for use with a single tool, so the risk of a direct short is minimal, and the output current is limited to a modest value as the input is typically fused via a 13A plug.

    I believe they have earth connections to the transformer for safety too, you would end up with an isolation transformer but if one side of the output became grounded (under single fault condition) the other side will be at 110v WRT earth.

    the centre tap arrangement is very similar to the American domestic supply set up. apart from the fact that our friends across the pond refer to the centre tap connection as neutral and the two outer conductors as live

    that type of transformer is used for 110V items with a voltage to ground of 55V.

  20. Tomi Engdahl says:

    The Power Grid, Isolation Transformers and Earthing

    In order to explain the idea behind some isolation transformer units I’m working on at the moment, I explore the power grid, safety features of electric installations, Earthings Systems and RCDs.


    3 vuotta sitten
    Excellent video. Fantastic explanation.
    In the USA in some states ( Mid-West e.g. Kansas, Oklahoma ) the primary distribution Voltage (7.2 or 14.4 kV) if often 4 wire Y configuration. with one Earthed High Voltage conductor. It may be because of the thunderstorms encountered in those areas. Also SWER systems can be employed without an isolation transformer. The House Voltages are 120 – 0 – 120 Volts. or 240 Volts 60 Hz between the outer two

    Joshua Mudge
    2 vuotta sitten
    Fantastic video. I found several things very fascinating about how you, Germans, treat your power system.

    Here in the U.S.A. residential clients do use a split phase system with a center tapped transformer. The primary winding is connected to 2 legs of the 3 phase lines, which are usually about 5kVrms in residential neighborhoods. The 2 legs of power distributed throughout the home have opposite polarities and add to 240Vrms when connected together and 120Vrms with respect to ground. Typically high current loads use a connector with both power legs and a ground, sometimes they also include the neutral.

    Commercial clients will usually have a 3-phase star/wye transformer secondary with voltages of 120Vrms with respect to ground and 208Vrms from line-to-line. Industrial factories or workshops will sometimes have voltages of 208/410Vrms. Also, you may occasionally see a High-leg delta secondary with voltages of 120, 208, 120 with respect to ground. This uses one grounded center tapped transformer in the typical Delta configuration.

    The neutral conductor should only be bonded to the safety ground at one location, usually right after the service entrance. I found it interesting that your system actually uses a ground point at the pole as well, since this could cause unwanted telluric currents to run along the neutral line between the two ground points. Additionally, to be UL listed all isolation transformers must be grounded on the secondary wiring.

    I also found it intriguing that all of your circuits are GFI protected. Here only outdoor outlets and ones installed near water must have this protection. They also must trip at 6mA. Do you encounter any nuisance trips with single phase motors?

  21. Tomi Engdahl says:

    Voltage Values

    In the following, “voltage” means the voltage between the conductors. The standard voltage values used are:

    1. Extra low voltage (ELV) – means any voltage not exceeding 50V a.c. or 120V ripple free d.c.
    2. Low voltage – means any voltage exceeding 50V a.c. or 120V ripple free d.c. but not exceeding 1kV a.c. or 1.5kV d.c.
    3. High voltage (HV) – means and voltage exceeding 1kV a.c. or 1.5kV d.c.
    4. Extra high voltage (EHV) means any voltage exceeding 220kV.

    Used to supply customers installations
    240/415V (3 phase)
    240/480V (1 phase)

    Used for urban and rural HV distribution
    12.7kV (SWER)

    Used for sub-transmission of larger power levels in distribution over middle distances

    Used for transmission of large power levels over long distance

  22. Tomi Engdahl says:

    How the delta 3 phase system works

    This one covers the wiring of the the delta 3 phase system.

    How the 3 phase math works (277 + 277 = 480?)

    This is a quick run through of how we add up phase voltages to get our line voltages.


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