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Around most built up areas of NSW you will notice the lower level has 4 wires, and there is often an upper level with 3. Why?
This is due to 3 phase power distribution.
If you connect a LED and resistor, or a lamp, to a battery of the appropriate voltage, a current will flow in one direction, from positive (+) to negative (-). In any case, the current will be fairly constant, diminishing only as the battery drains, and its voltage, and thus ability to push current through a particular load decreases. With a load like a battery powered radio receiver the current may vary up and down in time with the volume of the speech or music, but it will always be in the one direction. The internal resistance of the battery also rises with discharge, also limiting its ability to supply energy.
That said, in something like portable ham radio station consisting of a small solar panel, a battery, and radio, then current can flow into the battery, charging it, and out of it when they radio transmits, discharging the battery. The voltage is always positive relative to the negative terminal, but the direction of the current can vary. A car with a generator (alternator (containing rectifiers) if modern; a dynamo if old) does this too, with the possibility that discharge can occur, if headlights, radio, communications gear, blowers, and rear demister are all on, while idling in traffic.
Note that the + to - flow is conventional current flow. Your science / physics teacher often spoke of electron flow. That electrons flowed in the opposite direction to conventional current perhaps only become obvious when current flow in "thermionic valves", aka "electron tubes" became apparent as current flow only occurred when the cathode / filament was heated, and electrons "boiled off" and were attracted to the positive electrode.
Commercially supplied, or "utility" power is usually delivered as single or three phase.
An ordinary Australian outlet has 3 slots, the top 2 carrying power, and the lower, vertical one, the protective earth.
The left is the active, and is (usually) one of the 3 phases. The right is the neutral. There is 240 volts RMS between active and neutral. At the switchboard / fuse box / meter box the neutral is "bonded" or connected to an earth rod and metallic water pipes, if present.
240 volts is now officially "230 volts" with a large upwards tolerance, so can rise to about 250 volts, or sag to around 220 volts.
The active is also called line, hot, or phase. This swings positive and negative with respect to neutral, through 50 full cycles each second. We now honour a radio pioneer, Heinrich Hertz, by measuring such a frequency in Hertz. Active was also called Live, especially in the UK, however, both the active and neutral are now considered live, as they carry current. Dodgy wiring by lazy sparkies can put 240 on a disconnected neutral via a different circuit "borrowing" the neutral, say between upstairs and downstairs lighting circuits, especially around the stairs.
This is not a rapid (square-wave) switching back and forth, but follows a smooth sine wave. AC power has the big advantage that the voltage can be stepped up and down using a transformer, be it a huge unit in a switch yard, or a small plug-pack.
Where power is derived from a small generator or inverter the system is pure single phase.
Larger loads, especially motors, use 3 active connections, or phases, occurring 120 degrees apart. Three phases can also be used in large offices, or multi-unit residential developments, with single-phase loads shared between phases.
This is called a star arrangement, or "wye" by Americans, for the uppercase letter Y.
At the moment that the A phase is at its positive peak, the B and C phases are both somewhat negative. At that moment there are zero volts between B and C.
Thus, the full 3 phase system uses 5 wires: The three phase (active) wires, the neutral, and the earth.
 |
| Three wire medium voltage distribution at the top, likely 11 kV at the top, and 4 wire 240 / 415 volt wires at the bottom. Given multiple connections to the left-most wire (nearest properties) this is the neutral. The further house has two phases, the nearer only one. The fine wire is a switched active for street lights, no longer used as the new LED lights contain a sensor. |
On poles, low voltage 3 phase power uses 4 wires. Except around some railway properties, a specific earth is not used on "low-voltage" aerial power distribution. Occasionally these are in the form of Aerial Bundled Conductor, or ABC. These were placed around the upper North Shore of Sydney following the 1991 storm.
Many motors use a delta connection, so they only need the three phase connections, and earth. Between each phase there is 415 volts, now officially 400 volts. Some Europeans will see closer to 380 volts.
Plugs can be 4 pin for a lot of equipment containing motors, having the three phases and earth. A workshop or factory compressor with only a pressure switch is an example. Motors which are star connects can have an floating neutral point. Where a machine contains electronic control systems a 240 volt supply may be used, perhaps along with low current devices and perhaps small fans, a neutral would likely be included. EVSEs (AC "chargers" for EVs), things like stage lighting dimmer racks, and portable power distribution boards for racks of amplifiers and audio gear at a show need a neutral. This 5 pin plugs are needed.
A big advantage of three phase is that, provided the connection is correct, motors will start in the correct direction, and start reliably. I have certainly noted the microwave oven motors, clearly single phase, sometimes start in different directions. In this case it doesn't matter, but in things like fans, it is important; and in industrial equipment, often vital to prevent damage to the equipment.
One risk is that a power company might do line work, or replace a transformer, and reconnect the 3 phases in the wrong order, which can cause thousands of dollars damage, although smart relays are available, which prevent equipment starting backwards. Swapping any two phases will reverse the motor.
Large heating loads, and commercial water heating can also use 3 phase power. The local branch of a global hamburger merchant where I grew up had a water heater the same size as our domestic off-peak system, but instead of one 20 amp, 240 volt, 4.8 kW element, there were six, two on each phase, totalling 28.8 kW. 40 amps per phase means a fairly easy to handle cable with 10 mm² wires can be used, rather than one with chunky 50 mm² wires, required to carry 120 amps in a single phase system. The overall diameters of the cable are 18 mm vs 29 mm, and the price per metre of A$50 vs A$160 (!).
Occasionally a house will have 2 of the 3 phases connected. This is simply about splitting current between the phases, not running higher voltage loads, although this higher voltage occurs in the switchboard. A few decades ago the supply authority in my part of rural NSW decided this was a good idea. That is how these multimeter images were taken.
Multi-dwelling locations will often split units across all three phases, but only 1 phase per unit for simpler metering.
A number often often large loads use DC at a range of voltages. This can be 1500 volts on many suburban / inter-urban trains. Trams / light rail vehicles often use DC at between 600 and 750 volts. The Washington area Metro also uses 750 volts DC, so DC in DC. Traditional telephone exchanges use 24 cells floated at around 53.5 volts, called 48 volts or 50 volts. Consumer electronics uses voltages such as 5, 6, 9, or 12 volts DC internally; Hi-Fi gear somewhat greater voltages, professional PA gear plus and minus 40 to 50 volts.
For trains and commercial LR / Trams voltage is stepped down from medium voltage to an appropriate voltages, using a transformer, and rectified using diodes of various types. For telephone exchanges, and domestic gear it is stepped down from mains voltages, and rectified. Tram museums usually step 400 volt mains up, typically to 600 volts for historic trams.
In days of old rectifiers, aka diodes, were expensive, as they were either an electron tube / thermionic valve, or stacks of selenium rectifiers. Even in 1968 when 1N400x series were a new product, a silicon diode might cost 25 cents each, more than a loaf of bread, or a bottle of milk (568 ml (1 real pint), or 600 ml). Thus a full bridge of 4 might cost an apprentice an hour's pay to buy! Therefore many circuits used a single diode for many years. One even appears in the current US Technician paper question pool, although when the purpose is component or symbol identification, this is sensible. This forms a "half wave rectifier" where only the forwards or positive going part of the cycle is used. This means that there are 50 pulses per second, with periods with no current flow. In most cases a capacitor use used to make smoothed DC. They do this by charging to the peak voltage of the AC, then powering the circuit during the periods between these peaks. However, the long periods between charging the capacitor means that there can be a 50 Hertz hum on the output of any audio devices powered this way.
There is a "full wave" rectifier using a centre-tapped transformer and two diodes. This pattern was also popular with valve featuring 2 anodes and a directly heated cathode. A separate 5 volt winding was used, and this was often elevated hundreds of volts above the cathodes heated by the 6.3 or 12.6 volt winding.
However, now that diodes are a dollar or so for 10 (although more at Jaycar, a few cents each in bulk), a "bridge rectifier" or "full bridge" can be made for small change. Better still, a 4 pin device can be bought for a few 10s of cents, or a bit more at retail. These prices apply for 1 amp devices, with prices growing in line with current and voltage ratings.
A full wave rectifier gives pulses for both forward and backwards parts of the cycle. I suppose the negative pulses becoming positive is the "rectification". The shorter duration between pulses means hum voltages should be less, but at 100 Hz. The unsmoothed waveform still varies between 0 and the peak voltage.
For much of the Americas (and part of Japan) the hum frequencies are 60 and 120 Hz.
Note that many devices needed low voltage DC a "switchmode" supply is used, which rectifies the mains, then uses an oscillator and small transformer operating an a frequency or 25 to 40 kHz, typically, then uses fast diode to rectify this.
If you've ever pushed a lawnmower, or perhaps ridden a V2 motorcycle, you will know both of these generate significant vibrations. Both are very noisy. A 4 stroke mower has 1 power pulse every second rotation. A flat twin (Boxer) is the only 2 cylinder format with both a 360 degree firing pattern and physical vibration minimisation compared to the V2 or many inline twin options.
Meanwhile many smooth, luxurious cars, such as Rovers, Jaguars, and earlier small Lexus models used, or in BMW's case, still use, inline-6 (aka straight-6) engines. Mazda has also adopted this format. These have three power stroked per rotation. A few double-up, and use a V12, such as the previous model (JDM) Toyota Century; some BMWs, and their Rolls Royce models, firing 6 times per revolution. Of course, an electric motor is the smoothest option.
Having fallen out of use, half-wave rectification using 3 diodes is possible, with a ripple frequency of 150 Hz. In unsmoothed form there is a large ripple voltage, falling to around half the peak voltage before the next phase kicks in.
A full wave rectification requires a centre-tapped transformer and 6 diodes, with a 300 Hz hum frequency. A mercury arc valve with a common cathode was one option for things such as producing DC railway or tramway power.
In a three phase system some level of voltage is available at all points of the cycle. Just 6 diodes are needed to rectify three phases. For a full bridge only 5 connections are needed. When unsmoothed DC is taken from this rectifier then the ripple voltage is fairly small, around 13.3% of the peak, and given the very short delay between peaks, just 3.333 ms, ripple in smoothed DC is low, with any ripple at 300 Hz.
You can see diagrams on in my Circuits-1 page.
In countries which aren't the USA the following classes apply to AC voltages:
For DC the transitions are 120 volts and 1500 volts.
The LV range places the industrial use voltage of 690 volts delta in the range of regular electrician can work on, while allowing heavier motors to be driven, without recourse to voltages such as 3300 volts. These voltages require special class electricians, and special switch gear. Some regular breakers and motor controllers, etc, can handle this voltage. My understanding is that 400 volt transformer and motor windings can be used, turned from delta to star.
Uses include tollway extraction fans, and cranes on offshore oil platforms.
Please do NOT rely on this information, should you be a 400 volt person asked to work on a 690 volt system for the first time!
Regular US sparkies max out at 600 volts delta, although this 347 / 600 volt system is more popular in Canada, with 277 / 480 volts often popular in US commercial premises. Corner grounded 480 volt systems are also used, with the second phase, or phase B, connected to earth. In these cases the fuse(s) for this phase is/are replaced with link(s). There are also 240 volt and 600 volt corner ground systems. The US uses high-leg delta too.
If you look up the high-leg and wild-leg system, or other US stuff, remember (just under) 208 is half (just over) 415.
Taiwan uses corner grounded 110 volt, 60 Hz system. While standard US outlets are used by consumers, turn up with your ship and connect it to shore power, and things get very weird very fast! They count phases as R, S and T, with S grounded.
If there are three wires at the level above the 4 on poles which pass your house these are likely to be 11 kV (11,000 volts). These are in a delta connection, which is why only 3 wires are used. Three wires feed power into transformers which step the voltage down from 11 kV delta to 230 volts star, resulting in 400 volts delta. In areas built before maybe 1990 it is 240 / 415 volts, which can float above this close to the transformer. In WA it is 240 / 415 volts, with 254 / 440 volts used historically.
Going OT, along with something like 110 volts, 254 / 440 volts used on naval ships, with 460 volts on newer ones. Either way, using the shore power connector as a "used beer" receptacle has ended VERY badly for at least one person returning from shore leave.
In much of urban Australia this is a rectangular unit, and supplies tens of houses, and perhaps small businesses and schools. Many are on poles, or between two heavy poles, but "padmount" units may be on a concrete pad on the ground. In a large shopping centre, very large multi-unit or mixed business-residential development, this may be in the basement or utility area.
This voltage can be 22 kV, or occasionally 6,600 volts.
From where I grew up, it appears that the 11 kV might run up to 10 km.
The 11 kV comes from a local substation which steps the voltage down from a greater voltage. Voltages such as 33 kV, 66 kV are distributed on a single pole, and 132 kV on a single heavy pole, or on a two-pole and cross-bar arrangement. The latter voltage, and 330 kV, are the voltages typically on metal lattice pylons. Where 6 wires, or six sets of 2 or 4 wires in tight groupings are used, there are two three-phase circuits on the pylon. Outside NSW a single circuit using 3 wires can be run on metal pylons, although partly this can be down to metal not being appetising for termites.
In all but the most remote areas of NSW three phase is used. It these cases poles with three wires, carrying a medium voltage roughly follow roads, but are often on farm property, so they get hit by tractors instead of cars. Near each farmhouse wires branch off, carrying two, or occasionally three wires. These connect to a small pole mounted transformer, either rectangular, or in a round can. In most cases there are two ceramic insulators connected to the medium voltage lines. Often lightning protection devices are included, with wires to an earth connection. From these a cable of two insulated wires connects to the farm house and/or out-buildings. Occasionally there may be poles carrying the two bare wires, instead.
Periodically there can be rectangular pole mounted transformers taking the sagging voltage back up to a little over 11 kV.
However, cross the river into Victoria, or go to South Australia, and you will often find SWER, or Single Wire Earth Return. This is a single wire, and 22 kV appears to be common. The distribution voltage is connected to a single input with a ceramic insulator as a feed-in, and often some sort of lightning protection. The other side of the transformer primary is connected to the can, and to an earth stake. The output is either 240 volts single phase, or 480 volts as a split-phase system, with 240 volts actives, 180 degrees apart. Large loads (milk processing gear, etc) connects between the two actives. Do NOT use this pole to "go behind a tree", as you may have an unpleasant experience. This is because there is a voltage gradient in the ground around the pole.
In either case this is still single phase. All three wires into the transformer are necessary for a three phase output, suitable for some dairy or similar large equipment. In this case a small rectangular transformer is used.
The US tends to do local distribution at 13,800 volts or similar, using a star arrangement. They do this because a variation on single phase called "split phase" is used, with a round single phase "pole-pig" transformer for each house or few houses, and they are concerned large loads with unbalance the system if a neutral is not used. This has two hots, at 120 volts and 180 degrees apart, giving 240 volts to power large capacity clothes dryers, cookers, heating and air-conditioning, and EVs via Tpre 1 / CCS1 / J1772 or NACS, at up to 80 amps AC, while lamps, PCs, TVs, fridges, microwaves, most ham radio gear (except well engineered high power linear amplifiers), etc, are between one or other of the hots, and neutral. Businesses can choose things like 240-0-240 split phase, or a range of 3 phase systems, including the unusual high-leg system, to suit their equipment.
At least in Toronto star connected medium voltage using the low voltage neutral as its neutral (both would be grounded anyway, and the current is only around an amp for each transformer, were the current unbalanced. One group of 3 pole pigs will provide 120 / 208 volts three phase, the next a 346 / 600 volts group (also termed 347 / 600 volts). There are are thus upper and lower ABC bundles with the medium volt wires above. NYC and parts of Miami also uses 120 / 208 wide area distribution.
Near railway lines voltages such as 6.6 or 11 kV, and 66 kV will be distributed on their own network to power their substations which transform and rectify the 3-phase power to the 1500 volt overhead supply. They often power stations too, and these may have both railway and commercial power, for redundancy. Thus the nearby shops, etc may have no power, but the station will. In NSW all distribution to railway infrastructure is at "utility" frequency, 50 Hz. Historic 25 Hz supplies for rotary converters or synchronous converters have been discontinued in Australia. Signals also use this supply, so this system does carry on into rural areas, beyond the overhead.
Small loads can be powered by a transformer between two of the 3 phase wires, as on farms.
In NSW the pole will often have a small yellow plate with a circuit number, and the voltage on it. Often there is more than one, as there are more than one set of wires. It may include the old Cityrail corporate symbol, similar to: ⇋
In parts of Australia, and overseas, voltages such as 25 kV at the "utility" frequency of 50 Hz are used for the overhead. In Germany and the Nordic countries 15 kV at 16.7 Hz is used, changed slightly from 16⅔ Hz, to avoid being an exact fraction of the mains frequency. The north-eastern US uses 11 kV or 12.5 kV at 25 Hz, derived from specific generators at some hydro plants, or rotary converters, plus a little 60 Hz utility frequency overhead.
These voltages are derived from higher voltage distribution systems, whether public or railway owned.
Various characteristics, such as voltage, of AC power have relationships expressed mathematically. These include between the star voltage of single phase, and the delta voltage of three phase.
When a voltage is quoted it is almost always the "RMS" voltage, standing for Root Mean Squared. This has the same heating effect as that DC voltage. This, for examples a 120 volt globe can be used on US household AC socket, or in a power station's control system battery.
The single phase or star voltage to three phase delta voltage relationship is to multiply by the square root of 3, √3. This is about 1.73205080757.
The delta voltage, named for the uppercase Greek Δ character. (And yes, the symbol is also used in maths to indicate change in a value, or a lowercase d may be used).
You can either do 433 / 1.7321 to get (about) 250 volts as suggested by the warning sign on some transformer cabinets in rural NSW, or multiply by the reciprocal, 0.57735026919, also getting 249.992666559 volts. These values do come out requiring some rounding, to get the published voltages.
Alternative terms: VLN is the line to neutral voltage. VLL is the Delta voltage, meaning the voltage between two phases (lines).
Note that voltages are in any case are nominal. Near a transformer the voltage can be 6% or more high, and at the end of a long cable, up to 10% low.
A range of values are:
| Star | Delta | Nominal |
|---|---|---|
| 110 | 190.525588832576 | |
| 115 | 199.185842870421 | 200? |
| 117 | 202.649944485559 | |
| 120 | 207.846096908265 | 208 |
| 127 | 219.970452561247 | 220 |
| 220 | 381.051177665153 | 380 |
| 230 | 398.371685740842 | 400 |
| 240 | 415.692193816531 | 415, 416 (US) |
| 250 | 433.012701892219 | |
| 260 | 450.333209967908 | |
| 264 | 457.261413198184 |
| Delta | Star | Nominal |
|---|---|---|
| 220 | 127.017059221718 | 127 |
| 230 | 132.790561913614 | |
| 433 | 249.992666559108 | 250 |
| 440 | 254.034118443435 | 254 |
| 460 | 265.581123827228 | 265, 264 |
| 480 | 277.12812921102 | 277 |
| 600 | 346.410161513776 | 347, 346 |
| 690 | 398.371685740842 | 400 |
Fortunately, if you square a square-rooted value, you get the original, so √3² = √3 × √3 = 3. Thus we can go from 230 to 690 volts without the 398.371685740842 volt step.
You can also get from 127 to 381 volts this way too, skipping 220 volts.
US (NEMA) motor rating system assumes voltage drops, so a motor with a nameplate voltage of 230 volts is used on 240 volts, 460 volts on 480 volts, and 575 volts on 600 volts. in IEC the motor plate and line voltage match. There are also motors designed for delta voltages ranging from 208 to 240 volts, as high-leg has a 240 volt delta voltage.
In single phase rectification, the RMS of the unsmoothed DC roughly translates to that of the AC input, noting that the diodes drop around 0.7 volts for a "full wave rectifier", or 1.4 volts in a full bridge.
When adequate capacitance is provided to give good smoothing, the DC voltage is the peak voltage of the AC waveform, less the rectifier drop.
Vpeak = Vrms x √2. √s is about 1.41421356237.
When we use an oscilloscope (don't connect these to the mains, unless you know exactly what you are doing) we see both the peak voltage (above the zero line), and twice this, the peak-to peak voltage, on the screen.Assuming a sine wave, to go from peak to RMS either divide by √2, or multiply by 0.70710678118 (or 0.7071).
For 120 volts, the peak to peak voltage is about 120 × 2.8284 = 339.411 volts. This appears in one of the US ham radio exams. For Aussies, this is the voltage inside a switchmode power supply, which rectifies the mains before reducing it to the desired voltage. Thus the typically 400 volt capacitor has a decent headroom.
Chargers are typically rated in kilowatts, or kW. For DC chargers working out the current needed to supply these is the problem of suppliers. For a user wanting to install a so-called AC charger, this requires some calculation. An AC charger is also called an EVSE, or "electric vehicle supply equipment". These are a smart outlet which supplies AC power to the vehicle's on-board charger.
Thankfully the calculations are pretty easy. For single phase the power (P) is the current (I) multiplied by the voltage (E, for electromotive force). P = I × E. You may have notices that a powerboard or power strip is typically marked "Max. Load 240 Volts 10 Amps 2400 Watts", which you can see is 10 × 240 = 2400. As the answer is in watts we can convert this this to kilowatts be dividing by 1000, giving 2.4 kW.
While we may be seeking current used at a certain power, we can see how much power our available supply can deliver using the formula above. In a rental or whatever you might be able to convince a Sky / Fox "News" watching landlord to allow an outlet for a "band saw", or some similar use. The limit is likely 15 amps. In units you need an outlet for a "buffer" or "vacuum cleaner", etc. I suppose the sparky chucked on a 15 A instead of the 10 amp, as he had run out of 10 amps - both sizes should be using 2.5 mm² cable anyway. Some locations limit single-phase loads to values such as 20 amps, and within this limit a 15 amp plus 10 amp double outlet can be used, as it is assumed that the smaller socket will be used at half its capacity, such 5 amps for an actual vacuum cleaner. Double 15 amp outlets require 4 mm² cable, and a 25 amp breaker (the step above the calculated 22.5 amps). Longer runs may require a step up in cable size to reduce voltage drop. If you have a double garage and 2 EV chargers, rate the cable breaker as required, or consider a circuit for each car.
I unsure if you can run say 32 amps to a sub-board in an outbuilding (garage) in Queensland, and then away from nosy meter readers who will interfere with your board if they see a single phase 32 amp breaker marked EV, have a single breaker for an EV in the garage, rather than say smaller breakers, one for a big saw, one for general purpose outlets for smaller tools and a radio, and one for lighting.
To get the current, based on power and the nominal (or measured) voltage, I = P / V. A salesperson claims a rate of 7 kW, and your power is 220 volts, 7 kW is 7000 watts. I = 7000 / 220 = 31.818 amps, meaning you need a 32 amp circuit, or better, and 6 mm² or better cable. You have 3 phase on your farm, so visit the BYD seller, and they say 11 kW. 11000 / 3 gives 3666.666 from each phase. You have 240 volts star voltage: 3666.66666667 / 240 = 15.2777 amps, and 2.5 mm² cable is fine if your wire run is short!
Note that most stand-alone US home have 120 volts for small to medium loads, but that the power connection is split phase system with 120 + 120 = 240 volts between the two Hots. This is used for clothes dryers (unless propane is used) and some heating, big Ham radio amplifiers, and electric car charging. Unit buildings may use 120 / 208 volts three phase. Some cars may accept 277 volts industrial power, but read the fine manual first.
And determining voltage? If P = I × E, and you want E, when you make the I disappear from that side you are dividing it by I, which you must also do to the P side, to keep the equation balanced, so E = P / I. A US Mustang Mach-E driver complained that his charging rate was low, so I worked out that instead of 240 volts across the split phase system he was getting just over 220 volts, or 110 volts per side. This may have been due to a lower line voltage from the days when it was 110, 115, or 117 volts, or more likely due to voltage drop in his wiring.
I forget the exact numbers but the poster said something like, "My car should charge at 12 kW, but is getting 11.05 kW instead". Assume the intention for 240 volts, so I = 12000 / 240 = 50 amps, so plug the 50 amps limit into the formula, thus E = 11050 / 50 = 221 volts. If you halve this you get 110.5 volts on each side, within tolerance, especially with this current draw.
Vehicles can also limit charge rate or current draw electronically, so you don't overload something like a motel room's power circuit.
For Single Phase this table has current settings down the left, in amps; and the voltage across the top, in volts. The results are in kilowatts, to three decimal places. You can also read it as watts of you ignore the dot, or treat it as the thousands separator, as Europeans do.
| 1 Ph | 220 | 230 | 240 | 277 | 120 | 127 | 208 |
|---|---|---|---|---|---|---|---|
| 6 | 1.320 | 1.380 | 1.440 | 1.662 | 0.720 | 0.762 | 1.248 |
| 8 | 1.760 | 1.840 | 1.920 | 2.216 | 0.960 | 1.016 | 1.664 |
| 10 | 2.200 | 2.300 | 2.400 | 2.770 | 1.200 | 1.270 | 2.080 |
| 12 | 2.640 | 2.760 | 2.880 | 3.324 | 1.440 | 1.524 | 2.496 |
| 13 | 2.860 | 2.990 | 3.120 | 3.601 | 1.560 | 1.651 | 2.704 |
| 15 | 3.300 | 3.450 | 3.600 | 4.155 | 1.800 | 1.905 | 3.120 |
| 16 | 3.520 | 3.680 | 3.840 | 4.432 | 1.920 | 2.032 | 3.328 |
| 20 | 4.400 | 4.600 | 4.800 | 5.540 | 2.400 | 2.540 | 4.160 |
| 25 | 5.500 | 5.750 | 6.000 | 6.925 | 3.000 | 3.175 | 5.200 |
| 30 | 6.600 | 6.900 | 7.200 | 8.310 | 3.600 | 3.810 | 6.240 |
| 32 | 7.040 | 7.360 | 7.680 | 8.864 | 3.840 | 4.064 | 6.656 |
| 40 | 8.800 | 9.200 | 9.600 | 11.080 | 4.800 | 5.080 | 8.320 |
| 50 | 11.000 | 11.500 | 12.000 | 13.850 | 6.000 | 6.350 | 10.400 |
| 63 | 13.860 | 14.490 | 15.120 | 17.451 | 7.560 | 8.001 | 13.104 |
| 80 | 17.600 | 18.400 | 19.200 | 22.160 | 9.600 | 10.160 | 16.640 |
For Three Phase it appears the power is used as three loads, each using the star (Y or wye) voltage. This differs from the calculation for 3-phase motors, shown below, although you end up with the same answer. With the possible exception of locations where the 230 volts in delta, such as much of Norway, and part of Germany, an EVs requires a 5 pin plug, 3 phases, neutral, and earth. US EVs don't have the option of using 3 phase, and their 3 phase power arrangements can be "interesting". So is Taiwan's, which is often corner grounded.
| 3 Ph | 220 | 230 | 240 | 277 | 120 | 127 |
|---|---|---|---|---|---|---|
| 6 | 3.960 | 4.140 | 4.320 | 4.986 | 2.160 | 2.286 |
| 8 | 5.280 | 5.520 | 5.760 | 6.648 | 2.880 | 3.048 |
| 10 | 6.600 | 6.900 | 7.200 | 8.310 | 3.600 | 3.810 |
| 12 | 7.920 | 8.280 | 8.640 | 9.972 | 4.320 | 4.572 |
| 13 | 8.580 | 8.970 | 9.360 | 10.803 | 4.680 | 4.953 |
| 15 | 9.900 | 10.350 | 10.800 | 12.465 | 5.400 | 5.715 |
| 16 | 10.560 | 11.040 | 11.520 | 13.296 | 5.760 | 6.096 |
| 20 | 13.200 | 13.800 | 14.400 | 16.620 | 7.200 | 7.620 |
| 25 | 16.500 | 17.250 | 18.000 | 20.775 | 9.000 | 9.525 |
| 30 | 19.800 | 20.700 | 21.600 | 24.930 | 10.800 | 11.430 |
| 32 | 21.120 | 22.080 | 23.040 | 26.592 | 11.520 | 12.192 |
| 40 | 26.400 | 27.600 | 28.800 | 33.240 | 14.400 | 15.240 |
| 50 | 33.000 | 34.500 | 36.000 | 41.550 | 18.000 | 19.050 |
| 63 | 41.580 | 43.470 | 45.360 | 52.353 | 22.680 | 24.003 |
| 80 | 52.800 | 55.200 | 57.600 | 66.480 | 28.800 | 30.480 |
A symbol similar to the null (empty set) or diameter symbol ∅ or the Nordic Ø / ø is used to indicate the number of phases a motor or other device uses, thus: 1∅ or 3∅. Often the slash is full sized, but the circle quite small. Lowercase phi, ɸ or φ also appears.
One of the power formulas is: P = √3 × VLL × I
This assumes equal currents in each phase.
This gives watts; divide by 1000 for kW. If the load is reactive you need to include multiplication by the power factor (which is less than 1) to get true power. Reactive means that the load has either inductive loads, such as motors or transformers, or is very capacitive, such as capacitor droppers in some LED lamps.
Given VLN = VLL / √3, P = 3 × VLN × I, as in the second table above.
DC chargers use industrial sized 3 phase supplies and rectifiers to provide very large amounts of DC power. Most sites have their own padmount transformer to step down from medium voltage, although consideration is being given to chargers connected directly to medium voltage (say 11 kV). If you are wondering why the DC charger cables don't melt or catch fire due to the hundreds of amps flowing through them, the chargers pump often coolant through them!
Workshop and depot DC chargers are available in the 30 to 60 kW range; some able to run off a 63 amp 3-phase plug, some from a 125 amp plug, or via fixed wiring. Plugs can be IEC 60309 in red (400 volt class), or Australian "Clipsal 56" or competing products, likely with 5 pins to include the neutral.
Yes, no, maybe: In many homes there is a correlation between AC being mostly present as the mains voltage, 240 or 120 volts, or both (and up to around 430 volts between phases in some cases, including inside ovens); and DC being things like 1.5 volt torch / flashlight batteries; 9 volts batteries in other devices, including hobbyist projects; and voltages such as 5V, 9V, 15V, or 20V in USB-C chargers. In these cases, this is true.
However, low voltage AC, such as the output of a small transformer, up to around 30 volts or so is generally safe. An example is the 16 volt AC supply used in model railways to power accessories such as lighting and signals. 12 volt AC garden lighting is also generally safe.
The fact that AC output supplies use small isolation transformers typically helps ensure safety. Low cost USB and other chargers straight from the likes of Temu, and some Amazon sellers, etc, may not provide the isolation products with genuine CE, NOM, C-Tick, UL, or similar markings, including the weird UK-CA or UK-NI do. These unapproved units, including some sold via $2 shops or dodgy petrol stations, etc, have certainly caused fatalities. Older approved DC supplies with the heft of a transformer should be safe.
UKCA (dash use varies as they letters are in a 2×2 grid)) was an utterly unnecessary, politically motivated, and mostly abandoned fall-out of Brexit, turbo-charging the weirdness, although maybe not quite to JD levels. UKNI avoids breaching the Good Friday Agreement, as Northern Ireland remains in the EU Customs Zone while also being in the UK. Other countries outside the European Economic Area have chosen to enforce CE requirement, as far away as Korea. Türkiye does too, as it is in the EU Customs Union. Don't vote stupid, folks.
Meanwhile the several hundred volts DC from roof-top solar panels can be dangerous if you were to cut through the insulation, or otherwise contact the metal inside the wires. Even some installers may not appreciate this! Valve or tube based equipment, especially high power Ham radio, broadcast, or similar amplifiers also uses high voltage DC, with the capacity to supply high current. The 2 kV inside a microwave oven will send you to the morgue in a few milliseconds; contact before or after the rectifier is equally deadly.
A second hazard from DC is that once an arc starts, it is harder to stop it. Many light switches and outlets in Australia have small text "A.C. ONLY", either visible, or internally. The reason is that they only open a small distance, and even though there is a snap action, the distance does not guarantee there will not be a significant arc at 240 volts DC. Such DC systems continued into the 1980 in some ares of Sydney city, to run lift motors, but these have been discontinued.
You will notice that ripple-free DC is considered Extra Low Voltage, in generally not a significant shock hazard until 120 volts DC, while the AC limit is 50 volts. AC or pulsing DC is more likely to interfere with the heart rhythms than clean DC, potentially causing ventricular fibrillation (VF). The peak voltage of an AC supply is √2, or 1.4142 times the RMS voltage, used to describe power systems. For 50 v AC this is 70.71 volts, so this does not fully account for the difference; the VF risk is part of it too. For American 120 volts AC the peak is 169.7 volts.
Be aware that modern toasters which contain an electronic timer often derive the 5 volts or so by tapping the element. ICs in some mains equipment may use capacitive droppers. So, yes there is only a few volts powering the circuit, but they may be at a lethal voltage above ground, especially if there is incorrect wiring.
Finally, car or truck battery can generate very large short circuit currents, potentially enough to make a spanner very hot, or to spray molten metal from a screwdriver. If you have cuts or scratches on your hands and carry a car battery with your thumbs around the terminals you can get a shock, drop the battery, and split the case, and thus have acid all over your feet. Automotive traction batteries can be around 400 volts, occasionally 800, and can supply very large currents, so clearly working on these requires great care, with a danger at least as great as tram overhead power.
If you had a low-cost HO train set as a child, with simple variable resistive speed control (you could feel the the windings of the wire-wound rheostat is you moved the control) you noticed they provided pretty "ordinary" speed control. Instead, VFDs are used in single and three phase motors. They are use to control motors in many industrial systems, and modern Electric Vehicles. Industrial units work by rectifying the mains to around 340 volts DC in Australia. Electronics (often using Insulated Gate Bipolar Transistors as the power devices) are switched at high speed to emulate sine waves of varying frequencies. In EVs the typically 400 volt battery voltage is applied to the three phase delta windings of the traction motors. This is why you see three heavy, orange sheathed cables going to the motor. Single or three phase motor are used to operate things like the air-conditioning compressors (also termed the heat pump), and coolant pumps to ensure the battery is kept at the right temperature. Anything related to the braking or steering systems are run by the 12 volt battery.
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Written by Julian Sortland, VK2YJS & AG6LE, March 2026.
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