In modern conditions of operation of electrical equipment, whether it is a production shop or a private house with powerful consumers, the issue of protection of electric networks becomes critically important. The denominations of circuit breakers exceeding 100 amps are no longer a rarity in the projects of power supply of cottages and townhouses. The growing number of energy-intensive appliances, such as heat pumps, recovery systems and electric vehicle charging stations, require a rethink of traditional approaches to induction switchgear.
Choice switch-off In this range of currents is not just buying a more powerful "switch", but a complex engineering task that requires taking into account many factors. Errors in the calculations or installation are unacceptable here, as the consequences can range from frequent false shutdowns to catastrophic failure of the entire wiring. It is important to understand that the circuit breaker protects not only the connected equipment, but also the cable itself, laid in the wall or the ground.
In this article we will analyze in detail the technical nuances of the operation of power machines, the features of their thermal and electromagnetic characteristics, as well as the rules of safe installation. You'll find out why. characteristic C It can be dangerous for some types of loads and how to correctly calculate the cross section of the cable under the input machine at 125 or 160 amps.
Physics of the process and the appointment of powerful machines
Automatic circuit breakers designed for currents above 100 A, perform two main functions: protection against overload and protection against short circuit. Unlike household models at 6-40 A, where the heating processes of the bimetallic plate occur faster, in powerful devices the inertia of thermal vents is higher. This allows you to withstand the initiation currents of powerful electric motors or transformers for a short time without false alarm.
Constructively power-machine It is a complex electromechanical device. Inside the case are an arc-extinguishing chambers of increased size, capable of extinguishing the high-power electric arc that occurs when the circuit is broken under load. The use of less powerful analogues in circuits with currents above 100 A will lead to instantaneous burnout of contacts and possible fire.
When choosing a machine, pay attention to the limiting power outage (PSC). For introductory groups in private homes, this parameter should be at least 6 kA, and preferably 10 kA.
Particular attention should be paid to contact materials. In devices at 100, 125, 160 amperes and above, silvering or special copper-based alloys are often used, providing minimal transient resistance. Any increase in the resistance at the point of contact with such currents leads to a colossal release of heat according to the Joule-Lentz law.
Types of uncouples and performance characteristics
The key parameter when choosing a machine is the time-current characteristic. For ranges above 100 A, the most common characteristics are B, C and D, each of which has its own purpose. Incorrect choice of the type of the unlock will lead to either permanent network shutdowns when starting equipment, or to a lack of protection in a real accident.
Characteristics B provides the operation of the electromagnetic cleavage at a short circuit current exceeding the nominal 3-5 times. This is ideal for active loads where the initiation currents are minimal. Characteristics C (5-10 denominations) is the standard for mixed loads with moderate starting currents, such as lighting and household appliances.
For industrial equipment and powerful engines, the characteristic is used D, which withstands the starting currents 10-20 times higher than the nominal value. If you are planning to install a powerful compressor or pump, it is this type of protection that will prevent the machine from knocking out at the time of launch.
- 🔥 Heat disengagement reacts to prolonged excess current and protects the cable from overheating.
- ⚡ Electromagnetic detachment It works instantly when shorted, turning off current in milliseconds.
- 🛡️ Independent releaser It allows you to remotely disable the machine, which is convenient for smart home systems.
Calculation of cable cross-section and temperature corrections
Selection cable Under a 100A and above machine requires careful calculation. Insufficient cross-section of the vein will lead to heating of the insulation, its melting and short circuit. The machine must shut down the network before the current reaches a value dangerous for a particular cable cross section.
When calculating, the method of laying must be considered. A cable laid in the ground or in a closed tray is cooled worse than one laid openly. For currents above 100 amperes, cables with large-sect aluminium veins are often used, as copper becomes too expensive and rigid to install.
⚠️ Warning: Never install a 125 A machine on a 50 mm2 cable if it is laid in a pipe or beam. The long-term permissible load current of such a cable may be below the threshold of the thermal release, which will lead to overheating.
It is also important to take into account the temperature factors. If the shield room is in a room with high temperature or under direct sunlight, the throughput of the machine is reduced. In such cases, special correction factors are required when choosing a nominal value.
Connection schemes and switching of large currents
Installation of introductory machines with a capacity of more than 100 A has its own technological features. The main problem is to ensure reliable contact. Poorly clamped wire at a current of 100-160 amperes will begin to warm up instantly, which will lead to burnout of the terminal group.
For large-span cables (35 mm2 and above), the use of standard screw clips is often inconvenient or insufficient. In such cases, cable tips pressed with a hydraulic or mechanical press are used. The use of soldering for such sections is prohibited due to the effect of "fluidity" solder under load.
☑️ Checking the connection of the introductory machine
When assembling a switchboard, it is important to observe the correct location of the machines. Power machines emit a significant amount of heat, so they must be installed with respect to thermal gaps. Tight installation in one row without ventilation can lead to thermal acceleration and false shutdowns.
| Score of the machine (A) | Min. copper section (mm2) | Min. aluminium cross-section (mm2) | Max. power (kW, 380V) |
|---|---|---|---|
| 100 | 25 | 35 | 65 |
| 125 | 35 | 50 | 82 |
| 160 | 50 | 70 | 105 |
| 200 | 70 | 95 | 131 |
| 250 | 95 | 120 | 164 |
Protection Selectivity in Multi-Level Systems
In systems with input automatons above 100 A, selectivity becomes critical. This is a property of the electrical network, in which, if a short circuit or overload occurs, only the emergency section is turned off, and the rest of the network continues to work.
To ensure selectivity between the input automaton (e.g., 160 A) and group automata (e.g., 40–63 A), time and current selectivity must be observed. Often for this purpose, automatic machines with adjustable thermal and electromagnetic cleavers are used, allowing you to adjust the logic of the entire system.
What is time selectivity?
This is a delay setting of the higher machine. While the lower machine tries to turn off the accident, the upper one is waiting. If the bottom fails, the top is turned off.
Ignoring the principles of selectivity can lead to the fact that a short circuit in one socket in the kitchen will turn off the entire house, including the boiler room and ventilation system. In winter, this can lead to the defrosting of the heating system.
Problems with false positives and their solution
One of the common problems when using powerful machines is false positives. They can be caused by various factors, from the banal heating of the shield sun to the harmonic distortions in the network created by the pulsed power supplies of modern electronics.
Often users are faced with a situation when the machine knocks out at the same time turning on several powerful devices, although the total current does not formally exceed the nominal value. It's related to the fact that trigger-current summed up and can briefly reach values sufficient to trigger the electromagnetic cutoff.
If the machine knocks out regularly, do not rush to change it to a more powerful one. First, check the quality of tightening contacts and the real load of current-measuring mites.
The solution could be to replace the machine with a device with a different time-current characteristic (for example, with C on D) or install smooth start devices for powerful consumers. It is also worth checking whether the machine itself is warming due to poor contact on the input.
Frequently Asked Questions (FAQ)
Can I replace the 100A with the 125A without changing the cable?
No, it's strictly forbidden. The cable should be designed for a current exceeding the nominal value of the machine. If the cable is designed for 100A, then when installing the machine 125A, it can burn up during overload, since the machine will not turn off the network in time.
Why does the automatic switch hum when loaded?
The buzzing can be caused by vibration of the electromagnetic coil when a current close to the trigger threshold flows, or by weakening of the screw connections. It can also be a sign of interturning within the coil.
Which company is better to buy machines above 100A?
For currents of this magnitude, it is recommended to use products of proven brands (ABB, Schneider Electric, Legrand, IEK PRO series). Cheap analogues may not provide the claimed shutdown ability when short-circuited.
Do I need to press a multi-core cable under the 160A machine?
Yes, I will. Large-section multi-core cables must be finished with tips. A direct clamp lived in the terminal of the machine will cause them to damage and worsen contact.
What to do if the 125A is warmed by the terminals?
It is necessary to immediately disconnect the network and check the time of tightening contacts. If the contacts are melted, the machine and cable tips are to be replaced. It is not possible to continue operation.