Three phase systems may or may not have a neutral wire. The neutral wire allows 3 phase systems to use a higher voltage while still supporting lower voltage 1 phase appliances. In high voltage 3 phase distribution situations it is common not to have a neutral wire as the loads can simply be connected between phases (phase-phase connection). 3 Phase Power Wiring Color Coding
The 3 phases are typically indicated visually in electrical diagrams by colors. The standards for these colors vary by country. See the 3 phase wiring color code table for details.
Conductors of a 3 phase system are usually marked by color code, to allow for balanced loading and to assure the correct phase rotation for 3 phase induction motors. Colors used vary widely and may adhere to old standards or to no standard at all, and sometimes vary even within an installation. However, the current National Electrical Code (2005) does not require color identification of conductors other than that of the neutral (white or white with a color stripe), the ground (green or green with a yellow stripe), or in the case of a High Leg Delta system, the High Leg must be identified with orange. Click here to read more on 3 Phase Wiring and Color Coding.
3 Phase Power Generation
There are several types of 3 phase power generators. These can vary from a utility power station, to a prime source power generator to portable diesel (and other fuels) generators, to 3 phase generators which run on 1 phase power (some models of phase converters). The most common fuel type are generally diesel generators. At a utility power station, an electrical generator converts mechanical power into a set of alternating electric currents (AC), one from each electromagnetic coil or winding of the power generator. The currents are sinusoidal functions of time, all at the same frequency but with different phases. In a three phase power system the phases are spaced equally, giving a phase separation of 120°. The frequency is typically 50 Hz in Europe and 60 Hz in the US (see List of countries with mains power plugs, voltages and frequencies). See Frequency Converters for changing 50 Hz to 60 Hz or the reverse of 60 Hz to 50 Hz frequency. (See also Motor-Generator Frequency Converters) Read more about 3 phase power generators and power generation here.
3 Phase Power Distribution and Transmission
After numerous further conversions in the transmission and distribution network the 3 phase power is finally transformed with a power transformer to the standard mains voltage (the voltage of "house" or "household" current in American English). This is done with step down 3 phase transformers. The power may already have been split into single phase at this point or it may still be three phase power. Where the step-down is 3 phase, the output of this transformer is usually star connected with the standard mains voltage (120V in North America and 230V in Europe) being the phase-neutral voltage. Another system commonly seen in the USA is to have a delta connected secondary on the step down transformer with a center tap on one of the windings supplying the ground and neutral. This allows for 240V 3 phase as well as three different single phase voltages (120V between two of the phases and the neutral, 208V between the third phase (sometimes known as a wild leg) and neutral and 240V between any two phases) to be made available from the same supply. Click here to read more about 3 phase distribution.
3 Phase Power Calculation
There are several mathematical 3 phase power calculations that you can use to calculate your 3 phase power distribution to make sure that your wiring distributes your load evenly maintaining a balanced system. These calculations are useful for many purposes including when you have single phase equipment and 3 phase equipment running on the same power lines. Read more about 3 phase power calculation here.
3 Phase Loads
The most common class of 3 phase load is the 3 phase electric motor. A 3 phase induction motor has a simple design, inherently high starting torque, and high efficiency. Such motors are applied in industry for 3 phase pumps, fans, blowers, compressors, conveyor drives, and many other types of motor-driven equipment. A 3 phase motor is more compact and less costly than a 1-phase motor of the same voltage class and rating; also 1-phase AC motors above 10 HP (7.5 kW) are not as efficient and thus not usually manufactured. Many times a 3 phase motor may be started with a soft start drive can be used to start a motor and without as much of an inrush current, or a variable frequency drive which can vary the speed of the motor. Large air conditioning equipment (for example, most York air conditioning units above 2.5 tons (8.8 kW) cooling capacity) use 3 phase motors for reasons of economy and efficiency. There are many other common 3 phase loads such as 3 phase welders, 3 phase battery chargers, 3 phase lasers, and 3 phase computer controlled equipment, etc. When the load includes sensitive electronics such as 3 phase computer equipment often it is isolated from the power source to protect it with isolation transformers. Read more about 3 phase power loads here.
3 Phase Loads from 3 Phase Power Generated on 1 Phase Power
There are many places and instances where 1 phase power is all that is available, or where the power company wants to charge tens, or even hundreds of thousands of dollars to install and supply 3 phase power. When this is the case a quality 3 phase generating phase converter can be run on 1 phase to power 3 phase equipment of any type. Click here to read more about powering 3 phase loads with 3 phase power generated from 1 phase power.
3 Phase Converters
Often the advantages of 3 phase motors, and other 3 phase equipment, make it worthwhile to convert single-phase power to 3 phase. Small and large customers, such as residential, rural businesses, or farm properties may not have access to a 3 phase supply, or may not want to pay for the extra cost of a 3 phase service, but may still wish to use 3 phase equipment. A 3 phase generating Rotary Phase Converter can benefit these situations or where high quality 3 phase power is required. Some of the Rotary Phase Converters manufactured today produce 3 phase power output that is better quality and will allow 3 phase equipment to run better and last longer than the 3 phase power from provided by a utility company. Such 3 phase converters may also allow the frequency (see also frequency converters) to be varied allowing for different equipment frequency requirements (50Hz, 60Hz, 400Hz, etc.) and also for motor speed control (VFDs). Some locomotives are driven by 3-phase motors with 3 phase converters converted from the incoming supply of either DC or 1 phase AC. The two main types of 1 phase to 3 phase converters are Rotary Phase Converters and Static Phase Converters.
One very important resource is the rating system that the U.S. Phase Converter Standards Organization offers of various phase converter types and technologies. Click here to read more about 3 phase converters. Read what this very important industry organization has to say about the different technologies. As a non-profit organization run by 3 phase converter specialized electricians the have excellent insight into this technology. Their wisdom gives a great run down on how Rotary Phase Converters produce some of the most balanced 3 phase power output of all the solutions available. On their site you can read about why Static Phase Converters can be harmful to the equipment it is intended to run due to the fact that they don't actually put out a 3rd phase. Today many people and individuals sell " Build Your Own Phase Converter Plans ", but these tend to be just a potentially damaging static phase converter and an electric motor giving a time consuming inferior solution. Other companies use circuit board controlled 3 phase systems that they call Digital Phase Converters. For milling machines and other 3 phase computer controlled machinery there are CNC Phase Converters. With all these choices it is valuable to be able to use this organizations comparisons with their rating system to carefully consider your options. They even have a useful phase converter purchasing checklist page. Some engineers also appreciate recommended sources for finding highly rated phase converters that their phase converter resource page provides.
Phase and Frequency Converters
There are several instances where the equipment may need not only the phase changed from 1-phase, or the rare 2-phase (in the US this is mostly used in Chicago) to 3 phase power, but also the frequency converted from 50Hz to 60Hz or 400Hz (400Hz is mostly used in ships and aircraft). Click here to read more about 3 phase frequency converters.
1 Phase Loads on 3 Phase Power
Single-phase loads may be connected to a 3 phase system in two ways. This can be done either by connecting across two live conductors (a phase-to-phase connection), or by connecting between a phase conductor and the system neutral, which is either connected to the center of the Y (star) secondary winding of the supply transformer, or is connected to the center one winding of a delta transformer (High leg Delta system). Single-phase loads should be distributed evenly between the phases of the 3 phase system for efficient use of the supply conductors and supply transformer. Click here to read more about connecting a 1 phase load to a 3 phase power supply line.
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