Power supply. input device. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power supply. input device. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric power supply

Introductory device provides automatic shutdown of all electrical wiring of the consumer in the event of a malfunction, and also allows you to disconnect the wiring during repairs or for a period of prolonged inactivity.

In modern apartment buildings, the input device is located in common vestibules or on stairwells, in one- and two-story buildings - usually outside on the wall.

The input device can be fuse or some other protective device, for example circuit breaker. For a single-family house, the rated current of the protective device is not more than 25 A. At the inputs to an apartment building or in cases where single-phase electrical receivers with a power of more than 1,3 kW are used, a device for a current of more than 25 A may be required.

When using a fuse, a switching device is added to it, for example, a batch switch or a knife switch (with an automatic switch, an additional switching device is not required).

Fuses, as well as single-pole circuit breakers, are mounted only in phase wires. Installation of these devices on the neutral wire is not allowed. The neutral wire line can only be broken when the phase wire lines are simultaneously broken. With a single-phase branch, this is ensured by two-pole switching or protective devices. A three-pole device can also be used, but with a single-phase (two-wire) input, one of the poles is not used.

The current-carrying parts of the input device must be protected from rain or snow inaccessible to accidental contact, therefore it is advisable to choose devices that are appropriate for protection and operating conditions, or to mount the input device in a metal or plastic case. The input devices installed on the outer wall of the house are protected with a tin, plastic or wooden casing. The distance from current-carrying non-insulated parts to the walls of the protective casing must be at least 10 mm.

There is an opinion that the installation of fuses in the line not only of the phase, but also of the neutral wires increases the reliability of protection. In fact, a break in the electrical circuit associated with the neutral wire, including when a fuse blows in its circuit, can lead to life-threatening consequences.

One of the means of ensuring safety in case of insulation failure is grounding, i.e., the connection of metal non-current-carrying parts of electrical equipment with a grounded neutral wire. If there is a fuse or a circuit breaker in the neutral wire circuit, then it can work and turn off the neutral wire, which is tantamount to turning off the neutral wire, which protects a person from electric shock.

It is not allowed to install single-pole protective or switching devices in the neutral conductor circuit.

When installing electrical wiring, carefully perform all connections according to the diagram.

The input device on the side of the branch from the overhead line is connected with insulated wires with a cross section of 4 or 6 mm2 (for copper, a cross section of 2,5 mm2 is allowed). Insulated wires are connected to the branch wires at the insulators on the wall of the building by the specialists of the network owner, and the consumer is connected to the input device. If the branch is made with a cable wire or cable, the current-carrying conductors are also connected to the input device by the specialists of the network owner. From the side of the entrance to the building, the consumer must make the wiring between the input device and the electric meter.

When installing any three- or single-phase input device without a switching device, the neutral wire of the branch is connected using a separate terminal clamp to the corresponding wire going to the meter. Twisting is allowed if the wires are welded or soldered, but in the conditions of individual construction, this work with aluminum wires is difficult to perform. Therefore, for connection, a contact clamp from some electrical device is used, for example, a single-socket clamp for wires with a cross section of up to 4 mm2, used in lamps, or a clamp from a junction box. The diameter of the contact screws should be 4-6 mm. If the connected wires are made of different metals, each is fixed with a separate screw.

The group network, more often used in backyard buildings, is single-phase and mounted, as a rule, in three groups. Group No. 1 is intended for powering lighting fixtures. Group No. 2 is used to connect 6 A socket outlets without protective (zeroing or grounding) contacts. Group No. 3 feeds electrical receivers that require grounding of the device case (for example, a stove). Protective contact sockets are connected to this group.

Mixed power supply of socket outlets and lighting is allowed.

It is impossible to combine zero conductors of different groups. Neither switches nor fuses may be inserted into the wire that serves to connect the protective contacts of socket outlets.

Power supply. Introductory device
Rice. 3. Group network power scheme:

a - multilinear; b - single-line with air input; c - single-line version with cable entry; 1 - air line; 2 - cable line (performed according to the project of external networks); 3 - bipolar package switch; 4 - counter; 5 - automatic switch; 6 - wire for grounding; 7 - introductory box; 8 - apartment shield; 9 - knife switch; 10 - fuses

The rated currents of the releases of the circuit breakers must be:

16 A - for a group and lighting network and a network of socket outlets for a current of 6-10 A in houses without household air conditioners;
25 A - for a network of socket outlets in houses with household air conditioners with a power of up to 1,3 kW, as well as for a group power line for household electrical appliances with a power of up to 4 kW;
25-32 A - for a group power line of an electric stove with a power of up to 5,8 kW;
40 A - for a group power line of an electric stove with a power of 5,9-8 kW.

Author: Bannikov E.A.

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