# How are single-phase and polyphase voltages used?

Figure 1: Single-phase and polyphase voltage generation. As illustrated in Figure 2, the electric service delivered to a dwelling is typically comprised of a single-phase (110) voltage supply with a center tap transformer. The center tap accepts two voltages (120 and 240 volts) from the single-phase supply. These divided signals are then applied to different parts of the lighting system.

Single-phase power is useful for applications requiring simple wiring systems, but it can be problematic for more advanced applications that require separate circuits for ground fault protection and other types of electrical safety features. For example, if you plan to use single-phase power to run appliances such as dishwashers or water heaters, you will need to make sure that these appliances are designed to operate on 110-volt power. Otherwise, they may be damaged by electricity from the hot wire of the center tap transformer.

In contrast, three-wire 120-volt polyphase power is available in most areas of the United States. Polyphase power is generated by dividing the line voltage into three separate phases that are transmitted onto different parts of the house via individual wires called "hot wires". This method provides much greater flexibility than single-phase power because certain types of appliances can be wired directly to one of the hot wires without using the center tap. For example, if your dwelling was built after 1980, there's a good chance that it uses three-wire 120-volt polyphase power instead of single-phase power.

## How many voltages can a single-phase transformer produce?

Solitary phase A transformer fed by a single alternating voltage on the primary winding, which may be represented by a single sine wave, To create different voltages, such as 120/240V, the secondary winding might be "divided" or "tapped." That is, one or more of the wires going into it would be connected together, so that they form one or more complete circuits. This would give rise to another set of voltages.

A single-phase transformer can produce an unlimited number of volts. The only limitation is the strength of the materials used in constructing the transformer. If two pieces of paper were stuck together, they could not hold much tension. But if iron plates were inserted between the sheets of paper, they could hold many times their own weight. Similarly, a single-phase transformer can take any voltage within its limits and still function properly. The only limitation is the strength of the material itself.

Electric power transmission lines use large numbers of single-phase transformers to step down the voltage from transmission levels to lower ones that are able to be handled by household wiring. A single line might have 20,000 volts AC coming out of it, but only about 120 volts AC after it has passed through all the transistors in a typical city area network. The action of stepping down the voltage is called "powering down" the line.

## What is the voltage of a single-phase light?

These two produce different voltages from the same power supply. For example, the phase-to-neutral voltage on a 120/208 three-phase system, which is typical in North America, is 120 volts and the phase-to-phase voltage is 208 volts. Single-phase lights may be linked phase-to-neutral, and three-phase motors can be connected to all three phases. However, most single-phase appliances are designed to operate from a line voltage between 110 and 130 volts; otherwise they would need additional circuitry to handle higher voltage levels when there is no power flowing through them.

The voltage of a single-phase light depends on the manufacturer, but it usually ranges from 11 to 40 volts. This means that a single-phase motor must be able to withstand about 44 to 176 volts depending on the manufacturer's specification. To protect themselves against high voltage, most single-phase appliances have some sort of voltage regulator built into their design. These devices reduce the voltage before it gets to the bulb, so it will last longer without burning out.

Single-phase appliances should not be connected directly to a three-phase power source or else they might get damaged. Instead, they should be connected to a special transformer called a "recloser" that takes the current off of one phase and distributes it across all the remaining ones. The recloser needs to be large enough to handle the total load on all the phases. Reclees can be found mostly on industrial sites where three-phase power is used for heavy machinery.

## What are the common voltages for single-phase power?

120/240 Volt Single Phase The voltage between the two legs (known as phase to phase or line to line) is 240V, while the voltage from phase to neutral is 120V. The phase to neutral voltage is identified by the 120/240 notation, followed by the phase to phase voltage. For example, if the phase to phase voltage is 120V then there is no need for a third wire in the cable and thus all cables must be of equal length. If one cable is longer than another then there will be some distance across which both cables are carrying current, so they will meet back up again once more within the shorter cable.

In most countries, electrical utilities supply electricity at 240 volts, but it can be converted into lower voltages by special devices known as transformers. These transformers decrease the voltage from the high voltage of the generator to a safe level for household use. A transformer cannot increase voltage, so it can't make 400 volts appear from just two lines. It can only reduce the voltage from 400 to 120 or 240 volts.

In addition, each country has its own regulations regarding what lengths of copper wiring can be used in homes. In some countries, only aluminum wiring can be used for residential applications, while other countries allow either type of wiring to be used.

##### Oscar Holstine

Oscar Holstine is an expert on batteries and electrical engineering. He knows all about how batteries work and what they're used for. If there's something that needs fixing with an electric device, Oscar can probably help!

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