A sharp power outage when the welding machine and a powerful compressor are simultaneously operating most often indicates that the installed 380 volt introductory automatic is selected incorrectly or has a malfunction of the thermal disengagement. The exact correspondence of the nominal current to the total load is a critical parameter for the safe operation of the three-phase network, since exceeding the permissible values leads to overheating of the contacts and melting of the insulation. Ignoring the starting currents when starting electric motors often causes false alarms, which disrupts the technological process and requires the re-energization of equipment.
The choice of a protective device requires taking into account not only the active, but also the reactive power of connected consumers, which is especially important for garages with professional equipment. Three-phase circuit breaker The circuit must be broken in all phases simultaneously when a short circuit or a long overload occurs in any of the lines. Incorrect calculation of the cable cross section and the nominal value of the machine creates a fire risk, since the wiring may not withstand current that has not yet reached the protection threshold.
In this article we will analyze the algorithm for equipment selection, consider the design features of various series and determine the order of safe installation. Understanding the principles of work electromagnetic and thermal The sluices will avoid common errors when assembling the shield. Competent organization of the introductory group ensures voltage stability and protects expensive electronics from jumps and phase distortion.
Criteria for the selection of denomination and characteristics
The main parameter in the selection is the nominal current, which should be less than or equal to the maximum permissible current for the cable used, but more than the sum of currents of simultaneously working consumers. For a three-phase network, the calculation is based on the power factor and the possible uneven distribution of the load over the phases. Nominal current of the machine is selected from the standard range of values, and always focus on the nearest smaller standard, if the calculated value is fractional.
An important characteristic is the type of time-current characteristic denoted by the Latin letters B, C or D. For garage use, where the active load and motors with moderate starting currents prevail, the optimal choice is considered to be the characteristic C. If the circuit is powered by powerful transformers or heavy start motors, a device with a characteristic will be required. D, which can withstand short-term overloads up to 10-14 denominations without turning off.
β οΈ Attention: Installation of the machine with a nominal value higher than the cross section of the input cable allows is strictly prohibited, as this will lead to fire of the wiring until the protection is triggered.
When choosing, you should also pay attention to the disconnecting ability, which for household and semi-professional needs is usually 6 kA. However, for objects located near transformer substations, where short circuit currents can be high, it is recommended to use devices with a value of 10 kA. Disconnection ensures that the machine will not burn and not weld in emergency mode, and reliably break the chain.
The design and principle of operation of the three-phase automatic machine
The three-phase automatic switch structurally is three single-pole automatic machines, combined in one housing with a common control lever system and platoon mechanism. Within each pole are sequentially connected thermal and electromagnetic The two-way chain provides double protection. The free-release mechanism guarantees the rupture of the contacts even if the handle is kept on in the case of an accident.
The heat disengagement is a bimetallic plate that bends when a current exceeds the nominal current passes and drives the shutdown mechanism through mechanical thrust. This process takes time, depending on the amount of overload: the higher the current, the faster the disconnection occurs. Electromagnetic detachment It works instantly at short circuit currents, creating a magnetic field that directly affects the movable core.
- π Contact group: made of silver-containing alloys to reduce resistance and prevent sticking during arc formation.
- π‘οΈ Thermal compensation: Modern models have ambient temperature compensation so that the air temperature does not affect the accuracy of the response.
- π§ Modularity: standard width of the case is a multiple of 18 mm, which makes it easy to mount the device on the DIN-rail in the shield.
It is important to understand that in a three-phase automaton, when any of the three poles are triggered, all three phases are switched off simultaneously. This is implemented through a system of levers and jumpers inside the body. This design is necessary to protect three-phase consumers, such as electric motors, from working in two phases, which inevitably leads to their overheating and failure.
Interior arrangement of the arc-extinguishing chamber
The arc chamber consists of a set of parallel plates covered with a special composition. When the circuit is broken under load, the resulting electric arc is drawn into the chamber, divided into several short arcs, cooled and extinguished. The quality of the cameraβs execution directly affects the life of the machine and its ability to withstand multiple inclusions under load.
Calculation of power and cross-section of the cable
For the correct selection of the input machine, you need to know the total power of all consumers who can work simultaneously. In a three-phase network with a capacity of 380 volts, the current is calculated according to the formula taking into account the linear voltage and power factor. The resulting current value is the base for the choice of nominal value, while necessarily leaving a margin of 10-15% for reliability.
The section of the inlet cable must correspond to the selected nominal of the machine so that the conductor is heated no higher than the permissible temperature. A copper wire with a 10 mm2 cross section usually withstands currents of up to 50-60 amperes depending on the method of laying, whereas an aluminum analog requires a larger cross section. Section lived is selected according to the tables of the PUE, taking into account the coefficients of reducing the load when laying in pipes or beams.
| Cable cross-section (mm2) | Materials | Rated current (A) | Recommended automatic (A) |
|---|---|---|---|
| 4 | Copper. | 32-36 | 25 |
| 6 | Copper. | 42-46 | 32-40 |
| 10 | Copper. | 55-60 | 50 |
| 16 | Copper. | 75-80 | 63 |
When calculating, it is important to take into account not only the active power (kW), but also the reactive component, especially if the garage is running asynchronous engines. Power factor cos Ο For such loads, it can be 0.7-0.8, which increases the total current in the circuit. Ignoring this factor leads to the fact that the machine, selected only by kilowatts, will constantly knock out when starting the equipment.
When laying a cable in the ground or in conditions of high ambient temperature, it is necessary to apply the reducing coefficients to the current load specified in the directories of the PEU.
Connection schemes and installation procedure
Installation of the input machine begins with the installation of it on the DIN-rail inside the switchboard. Connection of the feed wires from the meter is made to the upper terminals, and the outgoing line to the consumers is made to the lower ones. Compliance with this rule is critical, since in some designs, when connecting the bottom, the fixed contacts can be energized even when turned off.
Cleaning of insulation of wires should be made with a special tool so as not to damage the veins and ensure the maximum contact area. Before tightening the screws, it is recommended to use NSHVI tips for multi-core wires or tinder for monovils. Quality of contact directly affects the temperature at the joint site and prevents burnout of terminals.
- π Puff: screws terminal tighten with the force specified in the passport of the device, usually 2-3.5 Nm.
- π§ͺ Check: After installation, it is necessary to check the reliability of fastening the wires with a light swaying.
- π Isolation: All live parts should be covered with plastic plugs or modular covers.
β οΈ Warning: Before starting any work on installation or replacement of the machine, it is necessary to completely de-energize the introductory panel and make sure there is no voltage on the current parts.
After connecting phase conductors, a zero wire is necessarily connected if a four-pole automatic is used, or a zero bus in the shield for a three-pole variant. Grounding of the shield body and equipment is performed by a separate wire that does not pass through the automatic switch. Proper assembling of the circuit guarantees the safety and convenience of further operation of the electric grid.
βοΈ Pre-insertion check
Common Errors and How to Resolve Them
One of the most common mistakes is using machines from different manufacturers in the same chain or assembling a shield from devices with different disabling ability. This can lead to a violation of the selectivity of protection, when the entire house is turned off, not just the emergency line. Selectivity is achieved by the correct selection of time-current characteristics and denominations of higher and lower automata.
A frequent problem is poor contact in the terminals caused by the use of wires of different sections or oxidation of contacts. Over time, such a connection begins to warm, the plastic is melted, and the machine has to be changed along with the wiring section. Regular drawing of contacts (in 6-12 months after installation) helps to avoid this situation.
Another mistake is to install cheap Chinese analogues without certificates of conformity. Such devices may not turn off the circuit when short-circuited, which will lead to fire. Always require a quality certificate and check for holograms on the product body. Reliability of protection of life and property does not tolerate savings on components.
The main principle of safety: the machine protects the cable, not the device. The nominal value of the machine is always selected by the cross section of the cable, not by the load power.
Failure diagnosis and maintenance
In the process of operation, the introductory machine may require attention if it is noticed spontaneous disconnection or heating of the body. If the machine knocks immediately after turning on, most likely, there was a short circuit or overload protection worked in the circuit. For diagnosis, it is necessary to turn off all consumers and try to cock the lever: if it is not fixed, the machine itself is defective.
Heating of the housing or suitable wires indicates poor contact or prolonged operation at the face value. In the first case, you need to tighten the screws or replace the tips, in the second - to recalculate the load and, possibly, replace the machine with a more powerful one, but only after checking the cable cross section. Heat relay inside the machine is sensitive to temperature, so the shield should not be under direct sunlight.
Regular maintenance consists in external inspection, dust removal and check of reliability of fastening. Once a year, it is recommended to carry out preventive switching on and off of the machine to develop the mechanism, which will prevent it from jamming. If traces of soot, melting or the characteristic smell of burning are detected, the device should be immediately replaced.
How often should I change the introductory machine?
The life of the circuit breaker depends on the number of on/off cycles and currents flowing through it. In normal operation and the absence of emergency shutdowns, a quality device lasts 15-20 years. However, if the machine is often knocked out on overload or short circuit, its life is exhausted faster, and replacement may be required after 5-7 years.
Can you use single-pole machines instead of three-phase?
To protect three-phase lines, the use of three separate single-pole automatic machines is prohibited by the PUE rules. This is because in an accident in one phase, the other two will remain energized, which is dangerous for three-phase equipment and personnel. Only a three- or four-pole automaton guarantees simultaneous opening of all phases.
Why is the machine buzzing when working?
A buzz or crackling inside the machine indicates a vibration of the electromagnetic cleavage or poor contact. This can be caused by the passage of current close to the threshold of operation, or the defect of the product. If the buzz is accompanied by heating, the machine must be replaced, as this is a harbinger of breakdown.