Differential relays and differential automats are very similar devices. They differ in design and operating principle. Let’s examine their features and differences in more detail.
Basic Characteristics
A differential relay is a device that protects consumers from electric shock when directly contacting a conductive surface. For example, an uninsulated wire, an electrical appliance, or a case that has come under voltage.
Differential relay — devices necessary for protection against fires on equipment with damaged insulation and faulty wiring. These residual current devices (RCDs) disconnect the circuit when a imbalance in electric current occurs in the wiring.
The industry produces two types of differential relays:
- Type AС. These relays are designed to respond to leakage of sinusoidal alternating currents.
- Type A. Intended for installation in electrical circuits that supply equipment containing rectifiers or thyristors. That is, where leakage of both direct and alternating current occurs in case of insulation failure. The installation of such relays is indicated in the operation manuals of some household appliances.
How is a differential relay different from a differential automaton?
A differential relay or residual current device with a differential automaton has some similarities, especially externally, but their operating principles differ significantly. A differential relay involves performing an instantaneous vector analysis of current relative to phase – 0.
If the sum of the vectors differs from zero, the mechanism receives a signal to disconnect the circuit, i.e., it reacts to leakage of electric current. The differential automaton reacts to so-called overcurrents that occur during overloads and short circuits, although some of these devices also respond to earth leakage, performing the functions of both an automaton and a relay.
Since differential relays and automats are incredibly similar, it is quite difficult for an amateur electrician to distinguish them — knowledge of markings is necessary. It is also better to entrust the installation of devices capable of protecting against fires and, consequently, ensuring safety of life and health, to qualified professionals.
These units are mounted after the main meter in the electrical panel on a DIN rail. At 220 V voltage, they have two terminals for input and two for output. At industrial facilities and in places where 380 V voltage is supplied, four terminals are installed at both input and output. These nuances must be taken into account for proper operation of the devices.
