In North America, the terms 220V, 230V, and 240V all refer to the same system voltage level. However, 208V refers to a different system voltage level. In North America, the utility companies are required to deliver split phase 240VAC for residential use.
220-230-240 (depends on utility) is the standard nominal 1-phase voltage across both legs of the line (120 nominal being the voltage from either leg to neutral). Most devices designed for 220 will run on 208 and in shops all over the place this is commonly done.
In short, just because a 208v motor may be designed to run on 230v or 240v systems by using two power legs from the utility source, that doesn't mean that it will provide the same output efficiency. You will see differences in performance if you try to use 208v when 240v is typically required.
The most common commercial building electric service in North America is 120/208 volt wye, which is used to power 120 volt plug loads, lighting, and smaller HVAC systems. In larger facilities the voltage is 277/480 volt and used to power single phase 277 volt lighting and larger HVAC loads.
The formula is volts times the square root of 3, which happens to be rounded off to 1.732. For 2 lines each carrying 120 volts, the calculation for this is 120 volts times 1.732, and the result is rounded up to 208 volts. That's why we call it a 208 volt three-phase circuit, or a 208 volt 3 phase line.
120/208V single phase is derived from 208V three phase power. If viewed on an oscilloscope, the three voltage waveforms on the three “hot” conductors all peak at different times: each one is 120 degrees behind the next.
A 208V single phase water heater is connected to hot 1 and hot 2 plus ground wire. An 120V single phase standard outlet is connected to hot 1, neutral and ground wires. A 208V three phase, 20A, L21-20R outlet is connected to all three hot wires plus ground and neutral wires.
208 volts is Line-to-Line Voltage. This three Phase voltage is frequently used in small businesses.
Although phase balanced can occur, there is no neutral connection on 208 circuits, therefore no physical way for current to flow. The only purpose for a neutral would be for 120 convenience outlets.
In North America, the terms 220V, 230V, and 240V all refer to the same system voltage level. However, 208V refers to a different system voltage level. In North America, the utility companies are required to deliver split phase 240VAC for residential use. That is two 120VAC (+/- 5 %) legs.
208V is *not* the same as 240V. 208V is the voltage between phases of a 3-phase “Y” circuit that is 120V from neutral to any hot. 480V is the voltage between phases of a 3-phase “Y” circuit that's 277V from hot to neutral.
In a more general sense, this kind of AC power supply is called single phase because both voltage waveforms are in phase, or in step, with each other. The term “single phase” is a counterpoint to another kind of power system called “polyphase” which we are about to investigate in detail.
Any voltage can be supplied as three-phase. Various voltages are more popular in various parts of the world and in various usage situations. In the USA, 220-240 volt, three-phase has been used to some extent for small industrial installations, but 480 volts is much more popular for three-phase installations.
So, a 230 volt motor can operate as low as 207 volts. When a motor is rated at 208/230 volts this means the motor will operate at the 208 volt rating, not 10% under the 208 volt rating. The motors that are truly intended for 208 volts are nameplated for 200 volts.
Even though the system voltage of 3 phase 208 is within the -10% rating of the three phase 230 v motor, the 208 is allowed to vary to -10% or 187 volts -- and the motor will not work at that level.
Three phase and single phase are electricity supplies and it's the amount of power that is different. A single phase supply is smaller and most domestic houses with gas central heating need single phase and have this as standard. If you require two or more electricity meters then you need a three phase supply.
Some three-phase power supplies do use a fourth wire, which is a neutral wire. The two most common configurations of three-phase systems are known as wye and delta. A delta configuration has only three wires, while a wye configuration may have a fourth, neutral, wire.
The difference between 208V three phase, and 240V single phase, is how the voltage is derived. 240V single phase is obtained by taking a single leg of three-phase power. 208V three phase is obtained by taking two legs of three-phase power.
Look at the 'main switch' or 'normal supply main switch' on your switchboard. If the switch looks like three switches combined into one and is wider than 3 cm, you have 3-phase power. If it's a single switch and slim, you have single-phase power.
A three-phase connection, on the other hand, consists of three separate conductors that are needed for transmitting electricity. In a single-phase power supply system, the voltage may reach up to 230 Volts. But on a three-phase connection, it can carry a voltage of up to 415 Volts.
The USA has their own wiring colors for electrical circuits, black, red, and blue are used for 208 VAC three-phase; brown, orange and yellow are used for 480 VAC.
Like the 110 volt outlet, there are a few variations of the 220 volt outlet based on the size of the breaker and measured in Amps. However, in this case there are 3 common variations: 15 Amp, 20 Amp and 30 Amp.
If a three-phase supply is available, then the 24,000 watts are divided by 3, meaning that 8000 watts is being used per phase. Now the current per phase is also down to a third of what it would be with a single phase supply (about 30 amps per phase, rather than 100).