To prevent the serious consequences of a power line failure, it is necessary to install protective devices that de-energize the load in such a situation. Let's get acquainted with modern protection devices.
Design, principle of operation
The need to install emergency switches is strictly determined by the requirements of the PUE and other documents that comply with international IEC standards. To understand the difference between a differential circuit breaker (RCD) and a differential current circuit breaker (DCCB), you need to learn more about the design and operating principle of each device.
Circuit breaker (VA)
An increase in current in the conductor causes heating.Previously, when fuses were used, this caused the calibrated wire insert to burn out and de-energize the consumer. The voltage supply was restored after the cause of the accident was eliminated by turning on a new insert.
The machine uses two methods of protection, with power restored by pressing the start button after the cause of the accident has been eliminated:
1. During emergency heating, the bimetallic plate bends and triggers the thermal release of the contacts. After cooling, the plate restores its original shape. Such a system is inertial; it takes a short time to warm up the bimetal mass.
2. High response speed in case of current overload or short circuit is ensured by an inductive circuit breaker. An increase in current through the coil will draw the core inside the frame and open the contacts, disconnecting the load from the network.
To increase reliability, both methods are used simultaneously, preventing the wires from heating up when overloaded and does not react in any way to leakage.
Residual current device (RCD)
The residual current device is designed to interrupt the network when a leak is detected, creating a potential flow path to the ground when the insulation is broken. The principle of a differentiating transformer is used.
The phase and neutral of the electrical network pass inside the device along separate wires from input to output. These conductors are wound counter-winding on the core. There is a separate winding, the terminals of which are connected to the electromagnetic relay of the breaker.
The RCD works like this:
- In normal operation, the currents of the neutral and phase wires, forming one electrical circuit, are equal to each other.A magnetic field of the same magnitude, but of opposite direction, is mutually compensated without inducing voltage on the turns of the differential coil.
- A person or animal, exposed to a leakage voltage, passes current through its body. The total current of one winding increases, upsetting the balance. This leads to the appearance of voltage on the control winding, triggering the relay and disconnecting the network.
The power supply is restored by raising the switch flag.
The RCD protects against leakage. It does not respond to overload and short circuit, when the currents in the neutral and phase conductors increase equally.
Differential automatic motor (RCBO)
The device combines the capabilities of a circuit breaker and an RCD. The combined design turns off the network if a malfunction occurs, protecting against fire in the event of a short circuit in the line or electric shock to people when the insulation of wiring or structural elements of household appliances is damaged.
Application differences
The appearance of the difavtomat is very similar to the RCD. Both devices are equipped with terminal screw contacts for connecting wires; on the front cover there is a contact breaker flag and a “Test” button for checking functionality.
A careful study of the inscriptions will help to distinguish them:
- The protection operation current must be indicated. For an RCD they write, for example, 16A, and a difavtomat of the same rating is designated C16.
- A protection circuit is shown, where the circuit breaker has a thermal and inductive release in front of the current transformer.
Some manufacturers indicate the type of device on the housing cover.
The application of specific protection depends on the overall network distribution design.It is important to remember that the RCD cannot be used without an overcurrent circuit breaker. The cost of the automatic device is lower than the total price of the RCD and the automatic device.
