When installing a home electrical network, at least two wires are always installed - phase and neutral. Also, sometimes equipment requires a ground or protective zero connection for operation. Let's look at what a neutral wire is used for, what its purpose and features are, what the principle of its operation is and what aspects of its operation you need to know, how to determine in practice the presence of voltage in a conductor, what types of neutral exist in power lines, and also what rules must be followed when connecting zero and ground.
Modern power supply cables include 5 conductors - 3 phases, neutral and protection Source rusenergetics.ru
Calculation of current in the neutral wire with uneven load
- break or poor electrical contact of the neutral conductor at supply substations that act as sources of electric current, or in public distribution devices;
- phase imbalance in the network;
- insulation damage.
Insulation damage
Indication of voltage at the working zero is possible in the event of an electric current leak due to damage to the insulation of household electrical wiring or electrical appliances. A particularly great risk exists in networks with old electrical wiring that has served its standard life, the insulation of which has irretrievably lost its dielectric properties.
What to do?
Electric current is very dangerous, so you should not experiment with solving this problem yourself. In all the described cases, it is better to contact the power supply organization or a professional electrician. In the vast majority of cases, significant measures are required to assess the condition and circuits of both power and home networks.
As a preventive measure in case of network disruptions, it is worth considering installing a voltage relay or inverter stabilizer. The voltage relay will turn off the home network when the zero line breaks, and the inverter stabilizer, in addition to shutting down, has the functionality of regulating the voltage level.
20 Reply from Danilov21 2016-05-02 17:46:34
Re: Current through the neutral wire
There is unverified data that the current in the phases will also change
if there are any leaks from the installation, then a change in the grounding characteristics will also change the mode parameters. if there are guaranteed to be no leaks, the modes will remain unchanged.
in other words. if the current during double grounding is caused only by currents external to the installation, the mode will not change. If there are grounding currents expected by the installation, its mode will also change.
According to the standards, the grounding loop is made of steel. Hardware grounding can be copper or aluminum.
Neutral wire
A circuit breaker with an overrated current rating is installed. The group circuit breaker and the electrical wiring cable of this group are selected according to the planned power of the connected devices. Over-rating the circuit breaker and connecting a powerful household appliance will cause the wiring to heat up.
Expert opinion
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Phase and zero in electrics - the purpose of the phase and neutral wires. The insulation material of the cores and the cable sheath have very specific temperature characteristics, exceeding which leads to their destruction and melting. Ask, I'm in touch!
How does current flow in a single-phase network?
Any single-phase electrical circuit consists of two wires. Through one wire the current flows to the consumer, and through the other it returns back. If you open such a circuit, then no current will flow.
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Neutral wire - purpose, features
The neutral wire is a separate branch of the household electrical network with a neutral voltage value. In contrast, the phase wire has a potential of 220 V. There are the following number of features of the neutral conductor:
- As part of a household network, the conductor is connected to the solidly grounded neutral of the transformer or generator set.
- In single-phase systems, all electrical devices require the connection of a neutral and phase wire to operate. In this case, in the normal state, the zero is actually connected to ground, so there is no voltage in it. However, if this connection is broken while the device is running, the neutral wire will carry a voltage equal to the phase, that is, 220 V.
- In electrical circuits, the neutral is designated N or “0” and is painted blue or cyan. In earlier installation schemes, the working zero was combined with the protective zero. In this case, the conductor had a yellow-green tint, and in the drawings it was designated as PEN.
Standard single-phase cable - white phase, blue zero and yellow-green protection Source esr-energy.ru
For the operation of many modern household electrical appliances, not only a phase and neutral wire is required, but also ground. If zero is required to comply with electrical regulations, then grounding serves solely the purpose of consumer safety. Voltage on the grounding conductor appears only in an emergency situation - phase breakdown on metal elements of equipment.
For example, if a phase breakdown occurs on the body of a washing machine, the connected grounding conductor will immediately lead it into the ground, thereby reducing the potential on the device to the minimum safe level. Therefore, if a person touches it during operation, he will either not suffer at all or receive a minor discharge.
In the diagrams, “ground” is indicated by the letters PE, and the insulation of the wire itself is standardly yellow-green. In modern wiring diagrams, the combined zero and ground are, as before, designated by the PEN symbol, but the color of the core should be blue with striped yellow-green colors at the ends.
Purpose of conductors and their colors in the power supply cable according to GOST Source hammer-shop.ru
Purpose
The main role of zero in a standard household circuit, with a single phase connected to the device, is reduced to the return of residual electric current in a closed circuit. In 3-phase circuits, the main purpose of the neutral wire is to equalize the voltage between phase and zero. In this case, depending on the circuit option, the zero core solves the following problems:
- Same power consumption on each phase.
A break in the neutral wire will not lead to an emergency. Since the potential difference between zero and any of the phases always remains equally constant.
- Uneven load.
Devices with different powers are connected to the phases. If you allow a break or an increase in resistance on it, then the total voltage will begin to be distributed to each consumer. Moreover, the lower its power, the more phase voltage it will receive. As a result, the equipment will deteriorate and a fire may start in the room. To prevent this, a neutral conductor is connected to each consumer.
Connection diagram for a neutral wire in a 3-phase circuit Source studfile.net
- Star connection.
Phase voltage is determined by the degree of load on each phase. When the distribution is uniform, for example, when connecting a 3-phase electric motor, the return of the residual current will occur along one of the phase conductors, on which there will be no voltage at a particular moment. If the loads on each phase are different, phase voltage drops will occur, leading to malfunctions. The problem can be solved by connecting the neutral wire.
On a note! The role of the neutral wire is always paramount, so breaking it is extremely undesirable. For this reason, it is always installed directly in the circuit - without a fuse. Moreover, if it is not combined with the protective ground, the conductor is selected with a cross-section 2 times smaller than for the phases. This is due to the fact that the current at zero, as a rule, is either insignificant or completely absent.
Operating principle of the neutral wire
Electric current is supplied to the consumer from a transformer, which in turn lowers the high-voltage voltage to an acceptable 380 V. Moreover, the secondary winding of such a transformer is arranged according to a “star” circuit - when all three wires are connected at the “zero” point.
Connection diagram of phases in the neutral with a grounding loop Source abc-import.ru
See also: Catalog of companies that specialize in electrical work of any complexity
In this case, the opposite ends of the conductors are brought out to 3 terminals - A, B and C. Their connection at one point “zero” is connected to the grounding circuit at the substation itself. Here the neutral conductor is divided into 2 directions:
- PE wire, protective with a yellow-green insulating sheath.
- N-core, working zero, blue insulation.
The modern power supply system for residential areas is designated TN-S. In addition to 3 phases and zero, a protective PE wire is also supplied to the switchboard - 5 wires in total. In old systems, power supply was carried out in 4 wires - 3 phases and working zero. It was named TN-C. The neutral conductor in residential buildings that use different loads on each phase eliminates uneven loads and prevents power grid breakdowns.
Diagram of the TN-C type power supply system Source ezetek.ru
Basic aspects of the neutral wire
For successful and safe operation of household electrical equipment, every home owner needs to know the following aspects of the functioning of the neutral wire:
- Purpose of the PE wire.
Unlike the working neutral wire, the purpose of the PE-core is additional protection of the home. In the event of a breakdown of current on metal elements of equipment or a short circuit, the protective wire reduces the voltage potential in the emergency location and safely discharges electricity to the grounding circuit of the substation. This allows you to avoid dangerous electrical damage to your household and protect your property from fire.
The distribution of phases between consumers is carried out according to a “star” diagram - similar to a transformer at a substation. Thanks to this, there are no network interruptions due to load differences. However, malfunctions still occur periodically - due to non-standard connections, incorrectly selected wires and their general poor quality.
Diagram of the design of a TN-S type power supply system with a separate protective zero PE Source ezetek.ru
- Causes of zero and phase failure.
If the load on the systems exceeds the established limits, and the quality of the wires is not the best, a network break often occurs. Moreover, if one of the phases breaks, the remaining two remain in working condition due to voltage equalization through the neutral wire. Therefore, this situation is not dangerous for electrical equipment.
It's another matter when the break occurs in the transformer station itself. However, this phenomenon is classified as atypical and rare, since often this kind of interruption occurs due to the unprofessionalism of a team of electrical repairmen.
- Causes of short circuit.
A short circuit becomes possible when the neutral wire does not fulfill its intended purpose. That is, when the current at the substation does not pass to the ground loop, but is directed along external circuits. As a result, if all devices are turned off on one phase and remain on the other, then the current in it can increase to a linear value - 380 volts.
A short circuit can not only damage equipment and wiring, but also cause a fire Source rov-adm.su
Symmetrical load when connecting receivers in a star
The load is considered symmetrical when the reactive and active resistances of each phase are equal, that is, the equality holds:
The symmetry condition can also be expressed in terms of complex resistances Za = Zb = Zc.
A symmetrical load in the network occurs when three-phase electrical receivers are connected. We will assume that this system has a neutral wire.
For any of the phases with a symmetrical load, all formulas obtained for a single-phase network, for example for phase A, will be valid:
Since in a four-wire circuit Ua = Ub = Uc = Ul /, then with a symmetrical load:
The vector diagram for a symmetrical active-inductive load is shown above. From the above expressions and the vector diagram it follows that with a symmetrical load, a symmetrical system of currents is formed, therefore the current in the neutral wire will be equal to IN = Ia + Ib + Ic = 0.
From this we can conclude that with a symmetrical load, disconnecting the neutral wire will not lead to serious disruptions to the operation of electrical receivers, that is, there will be no change in phase voltages, shift angles, currents, or powers.
From the above it follows that with a symmetrical load there is no need for a neutral wire, and quite often in symmetrical systems the neutral wire is not used.
The power of a three-phase electrical energy receiver with a symmetrical load can be expressed by the formulas:
As a rule, for three-phase electrical energy receivers, linear voltages and currents are indicated as nominal parameters. Based on this, it is more expedient to express the power of a three-phase circuit also through linear voltages and currents, so we substitute linear values into formula (6) and get:
Example
To a three-phase electrical circuit with a linear voltage Ul = Uab = Ubc = Uca = 380 V, it is necessary to connect a three-phase electrical receiver, each phase of which is designed for a phase voltage of 220 V and has an active resistance rph = 10 Ohm and an inductive resistance xf = 10 Ohm, which are connected sequentially. It is necessary to determine the power, shift angles between currents and voltages (cos φ) and phase currents.
Solution
Each phase of the electrical energy consumer is designed for a voltage one time less than the rated voltage, then the phases of the consumer must be connected in a star. Since the load in this case is symmetrical, the neutral wire (neutral) does not need to be connected to the consumer.
Phase currents, shift angles cos φ, as well as phase resistances will have the form:
The active, reactive and apparent power of the receiver, as well as any phase, will be equal to:
The vector diagram for this system was given above.
What is a zero break?
To fully answer this question, it is necessary to provide examples of the normal operation of a three-phase power supply input circuit. As an example, we will give a simplified version with an input for a floor distribution board.
Scheme 1. Normal operation of the system
As can be seen from the figure, each of the apartments on the floor is powered from a separate phase (L1 - L3) and a common zero. Which forms a phase voltage of 220 volts (L1N=L2N=L3=220 V) in the household network of each apartment. In this case, a TN-CS power supply circuit is used, where a PE grounding bus is used, connected to the neutral in the building switchgear. The above system is balanced, since the load current in the phase wires is summed through the zero line, which reduces the likelihood of phase voltage imbalance.
Note that it is quite difficult to completely eliminate this phenomenon, since the load resistance at each phase may vary. For example, in apartment_1 the air conditioner and washing machine are turned on, in apartment_2 the owner turned on the boiler and electric stove, and in apartment_3 there are no residents and all household appliances are unplugged. As a result, voltage asymmetry will occur in a three-phase power system.
Now let's look at the network operation in abnormal mode, when the zero burns out.
