To turn off, conduct and turn off currents in the circuit, a special device is used - an automatic fuse. The device operates under conditions of a given time or abnormal phenomena of the electrical circuit - short circuits, power surges.
Features & Functions
The switch is a switching device that protects the cable line from the critical value of currents. It performs the following functions:
- prevention of damage to the conductors of the conductors during a phase or earth fault;
- switching sections of the circuit - turns individual zones on and off;
- protection against overload when connecting powerful equipment to a common network;
- switching off the power supply when short-circuit currents with limit values appear.
Switching devices are controlled manually using an electromagnetic drive or an electric motor.
Machine device
Electric circuit breaker is available in one, two, three and four pole design. The product includes the following components:
- contact system - three-stage, two-stage, single-stage;
- Arcing system - consists of chambers with narrow openings, with arcing gratings or combined chambers;
- release drive;
- auxiliary contacts.
Also, automatic fuses have trip units - relays with direct action.
Types of releases
The machine is equipped with two types of releases:
- Electromagnetic circuit protects the circuit from short circuits. It has the form of a coil with a central core on the spring. With the passage of currents, an electromagnetic field is formed, attracting the core to the coil.
- Thermal, preventing the impact on the circuit of overload currents. It is performed as a bimetallic plate of two materials with a different coefficient of expansion at the time of heating.
Overload occurs when electrical equipment with a load higher than the permissible one for a given network pops into the line.
Principle of operation
The device of the machine provides the specifics of its work. Consider the principle of operation of the device is an example of a single-pole model:
- The cable from the power line is connected to the top terminal, and consumer wires to the bottom.
- To enable, you must put the handle in the upper position, to disable - in the lower.
- At the moment of switching on, the platoon mechanism directs the movable contact to the stationary one. The hitch connects.
- The solenoid trip electromagnet operates on the principle of expelling the core from the center of the coil by an electromagnetic field.
The principle of operation of the circuit breaker - A cylindrical metal core presses the release mechanism lever.
- Due to the flexible jumper, the coil is in contact with the movable element. Its position is regulated by a threaded screw.
- The fixed contact, thrown to the upper terminal, acts as a stop for the movable. He closes the circuit when the disengagement mechanism is cocked.
- Contacts are automatically switched off at increased current load. Sparking indicates chain breakage. The spark suppressor extinguishes sparks. Smoke and residual gases are discharged through a special channel.
- The thermal release duplicates all stages of the electromagnetic core. The difference lies in pushing the lever with a curved bimetal plate.
The more the current increases, the more the plate bends.
Normal operation
In non-emergency mode, the machine works differently. The control knob is raised up, and current is supplied to the device through the power cable. The conductor is thrown to the top terminal. Then the current is directed to the fixed contacts, and from there to the movable ones. Currents are supplied to the solenoid coil through a flexible cable. After it, they enter the bimetallic element, from there - to the screw terminal at the bottom, and then to the electrical circuit to which the load is connected.
Terms of Use
The power fuse is available in 5 climatic categories and is designed for operation under the following conditions:
- installation at an altitude of up to 1000 m above sea level;
- the outside temperature is from -40 to +40 degrees excluding frost and dew;
- relative humidity of 90% (+20 degrees) and 50% (+40 degrees);
- premises without dust, aggressive concentration of vapors and gases; there is no explosive atmosphere and dust on the street;
- installation on a surface where drops of water, oil, radiation particles will not reach.
The dependence of the operational parameters of the circuit breakers on environmental conditions is prescribed in GOST 17516.1-90.
Instrument Classification
Based on the classification of PUEs, users can select devices in one of the categories.
MA
Available without thermal release. Models are suitable for a network to which powerful units are connected. An overcurrent relay is used as overload protection. A fuse protects the line against overcurrent in the event of a short circuit.
Class A
Sensitive modifications with the operation of the thermal release with an increase in current by 30%. Automata differ:
- a coil that de-energizes the network in 0.05 seconds when normal values are exceeded;
- bimetallic element - turns off the power after 20-30 seconds.
With the help of devices, the connection of circuits with semiconductors is organized.
Class B
Equipment is suitable if you have a private house or apartment. It is used to connect to outlet, lighting lines. It is characterized by:
- operation of the electromagnetic release with an increase in readings by 200% in 0.015 seconds;
- triggering a plate of bimetal after 4-5 seconds.
The starting current value for such a device should be minimal.
Class C
An automatic selective device can be delivered to a household network. The electromagnetic unit is triggered when the rated current is exceeded 5 times. The thermal release becomes active after 1.5 seconds. Class C devices are used on input.
Class D
They are used to organize a common power line as backup protection. Triggered when the main equipment can not de-energize the power supply in a timely manner. The rated current must exceed the norm 10 times.
Classes K and Z
The response time depends on the type of current in the network with an inductive type of load. The alternating current should be 12 times larger than the norm, the constant current should be 18. The electromagnetic solenoid is activated after 0.02 seconds, the thermal unit - with an increase in current by 5%.
Auto fuse specifications
The differential device must be selected on the basis of the rated tripping limit, the number of poles, time-current indicator and the rated current tripping.
Rated breaking capacity
This TTX of the machine indicates the range in which it will open the wiring to de-energize it and consumers. According to the rated breaking capacity there are devices:
- 4.5 kA - used as protection for the power line of a private house. The cable resistance is 0.05 Ohm, the current limit is 500 A;
- 6 kA - installed in a residential sector or public buildings with a resistance of 0.04 ohms and a current limit of 5.5 kA;
- by 10 kA - protect industrial installations, since current up to 10 000 A arises in a short line laid from the substation.
For domestic use, 6 kA models are suitable.
Number of poles
With this parameter, you can set the number of wires to connect. There are 4 modifications:
- Unipolar. On the switch, you can throw the tap cables and power, but it will protect only from fire. The neutral is located on the zero bus bypassing the machine. When turned off, the phase breaks.
- Bipolar. Simultaneously de-energize all wiring. They are used when a single-phase device (boiler, water heater) is connected. The machine is connected to it by 2 power wires and 2 tap wires.
- Tripolar. Used when there is a three-phase or four-phase type of power supply in the network. They are connected according to the pattern of a triangle or star.
- Four-pole. The device required for 6 wires (3 - phase, 3 - protection). Connection to 8 cables is allowed (4 - phase with neutral, 4 - discharge, i.e. phase and neutral).
The quadripole is used for current supply of industrial equipment.
Time-current indicator
The value at which the automatic device will turn off the network until a critical point is reached. Operation occurs:
- for 10 or more ms;
- for 6-10 ms;
- for 2.5-6 ms.
The larger the category, the less the network cable heats up.
Rated current
A characteristic that determines the response speed of the device with increasing current above the nominal value. There are modifications on the market:
- 1 and 2A - provide electricity to a small number of devices with a total capacity of not more than the capabilities of the device;
- 3A is an industrial version with a triangular three-phase connection;
- 6A, 10A and 16A - are used to power individual rooms and apartments;
- 16A - have 3 or 4 poles, are installed at the input with three-phase power;
- 20A, 25A, 32A - are installed to protect apartments with a large number of household appliances;
- 40A, 50A, 63A - high-power devices for industrial and construction lines.
Use modification 25A at the input for the apartment.
An automatic machine for 6, 16, 40 or 20 Amps is available in a closed or open case, mounted on a wall, in a special niche, or in a combined way. When installed in the control cabinet, it is fixed on the din rail. Manufacturers produce models with or without mechanical fasteners.
Features of electronic fuses and current limiters
An obsolete fuse will heat up when exposed to current. Some users put a jumper on the shield for the machine. A massive product disrupts the normal operation of the equipment, causing a fire.
For multiple protection, an electronic fuse is used with the functions:
- self-healing circuit after eliminating the source of failure;
- network recovery after human intervention.
Devices can notify of malfunctions by means of sound and light signals.
The second protection option is a current limiter. For this, a single-module stable current generator is used. The limit value is set by the manufacturers. It will not rise even when part of the circuit or the entire line has been short-circuited.
Stabilizers with thyristors and current sensors are switched on at the time of increasing load. The thyristor turns the circuit so that the output voltage becomes zero.
How many circuit breakers can be used
In one electrical panel, it is impossible to install a switch for the group-system differential switch with a value of more than 30 mA. PUEs do not prohibit the connection of several machines, provided that there is no current leakage. Before starting work, the group leakage should be calculated.
- A variable resistor to measure the actual indicator.
- Calculate the theoretical value based on p.7 PUE - 0.4 mA and 10 μA per 1 m of cable per 1 A load.
To choose the right amount of RCD, you will need:
- When connecting, for example, 3 RCDs for 16 A each add up the values.
- Multiply the resulting value by 0.4 mA.
- Calculate the footage of the wire according to the apartment scheme and multiply by 10 μA.
- Add up the values and find out the leak.
Clause 7.1.83 of the PUE reports that the maximum leakage should not exceed the maximum limit of the residual current device, which is 10 mA.
How many wires can be connected to one machine
It is allowed to connect no more than 2-3 conductors with the same cross section to one device. If there is one RCD and two automatic machines in the shield, 2 highways will be organized. If there is a difference in the cross sections of the cable, they are twisted and clamped.
If there is no possibility of combining the cores to the switchboard, they are twisted in a box and fed to the machines 1-2 cables. It is required to install modular terminals with latches on the din rail and power them from the switches. Such a decision provides for the presence of additional space in the distribution box.
A circuit breaker at the entrance to the apartment or house ensures the safety of the home electrical network. The device timely turns off the power when the specified threshold is exceeded. This protection prevents accidents, breakdowns of household appliances and personal injury.
