If anyone came across electricity, then they certainly heard about such concepts as phase and neutral wire. Their main distinguishing feature is their purpose. The wire connecting the zero point of the phases of the generator, the transformer with the zero point of the load, is called zero or neutral. It is called so because in some cases the current in it is zero, and neutral on the basis that it equally belongs to any of the phases.
Content
- Differences between phase and neutral wire
- Features of the neutral wire
- Classification of neutrals of power lines
- The response of electrical appliances to zero break
Differences between phase and neutral wire
The phase wire (phase) is designed to supply electricity to the consumer.
The purpose of the neutral wire (neutral or zero) is to equalize the voltage asymmetry at different load values in the phases.
It is connected to the zero points of the source and consumer when they are connected to a "star".
The connection of the neutral wire (three-phase four-wire network) is only possible when the source and load are connected in a "star".
When connected in a "triangle", there is no need for it, since the line and phase voltages in the phases are the same.
To understand the difference between line-to-line and phase-to-phase voltages, you need to understand that in a three-phase three-wire circuit, a line-to-line (voltage between two phase wires) is mainly 380 V, and the phase - voltage between phase and zero is √3 times less than about 220 V.
The neutral wire earned its name because when the devices are operating, the current in it, with the same load of three phases, is zero. Its resistance is not great. Therefore, when one or several phases are overloaded, the current in it will increase rapidly. In the lighting scheme, its presence is a prerequisite. Otherwise, uniformity of illumination is not guaranteed..
Depending on the role, the neutral wire can be working, protective, combined.
The worker is denoted by the Latin letter N and is performed in blue in European countries. In some other countries, the color may be gray or white.
Protective is designated PE. It is designed for safety in the event of potential contact with the body of the appliance. In normal mode, it is de-energized, and in the event of a breakdown it is a conductor that will divert a dangerous potential from the electrical appliance to the ground. The color of this vein is yellow-green.
In some systems, the neutral wire is combined with a protective. In this case, the marking will be marked as PEN and the color of this core will be blue with stripes at the ends in yellow-green.
Features of the neutral wire
The neutral wire prevents unwanted situations during emergency operation. Without it, in the event of a phase short circuit of two phases, the voltage in the third phase will instantly increase by √3 times. This will have a detrimental effect on the equipment that powers this source. If there is zero in such a situation, the voltage will not change.
If one of the phases is broken in a three-phase three-wire system (without zero), the voltage on the two remaining phases will decrease. They will be connected in series, and with this type of connection, the voltage is distributed between consumers depending on their resistance.
If one of the phases is broken in a three-phase four-wire system, the voltage in the two remaining phases will not change its value.
Fuses are not installed in the neutral wire because of its great importance, because its breakage is undesirable
Since most of the operating time of electrical installations, the current in this wire is either zero or insignificant, it makes no sense to make it the same section as the phase section. Most often, for reasons of economy, it has a smaller conductor cross-section than the cross-section of the phase conductors in one electrical installation. If the protective wire is not aligned with the zero wire, its cross-section is half that of the phase wire.
Classification of neutrals of power lines
The purpose of power lines is very diverse. And also a variety of equipment for their protection against leaks and short circuits. In this regard, neutrals are classified into three types:
- deafly grounded;
- isolated;
- effectively grounded.
If the power line with a voltage from 0.38 kV to 35 kV is short, and the number of connected consumers is large, then a dead-grounded neutral is used. Consumers of a three-phase load receive power due to three phases and zero, and a single-phase one - one of the phases and zero.
With an average length of power transmission lines with voltage from 2 kV to 35 kV and a small number of consumers connected to this line, isolated neutrals are used. They are widely used for connecting transformer substations in settlements, as well as powerful electrical equipment in industry.
In networks with a voltage of 110 kV and above, with a long length of power lines, an effectively grounded neutral is used.
The response of electrical appliances to zero break
If the common neutral wire in a multi-storey building breaks, then consumers will feel this as a result of a voltage surge in their electrical appliances.
The main factors that can lead to de-energizing the common zero:
- emergency situation at the substation;
- outdated wiring;
- the wiring was not done very well.
The phase to which more consumers of the apartment building are connected will be overloaded. The tension in it will decrease. In the phase to which the consumers are least connected, the voltage will increase sharply.
This will negatively affect the devices - a decrease in voltage will cause their ineffective operation, and an increase in voltage may lead to the failure of those that were connected at the moment. To protect yourself from such a situation, it is necessary to install an individual overvoltage limiter in the panel supplying a separate apartment. As soon as the voltage begins to exceed the permissible values, the limiter will quickly turn off the power.
If a zero break occurs directly in the apartment, then the electricity will disappear completely, but at the same time the phase will not turn off. The danger lies in the fact that it can go just to the zero wire. And if any electrical appliance was previously grounded to it, the body of this electrical appliance will be energized, or, in other words, it will start to "be shocked".
The main factors that contribute to the breakage of zero directly in the apartment can be called:
- unreliable connection of contacts;
- incorrectly selected conductor cross-section;
- outdated wiring.
These factors lead to excessive heating of the conductor. Due to the increased temperature, the place of connection of the contacts is oxidized, the wires of the wires overheat. And this, in turn, can lead to a fire..
