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[Did You Know?] Classification and Functions of Relays
Release date:
2025-09-03
Source:
A relay is an automatic control device that, in response to a specific input signal, either closes or opens a low‑current control circuit, thereby enabling remote control and protection. Currently, according to sources within Yuanze Relay’s R&D department, the relay’s input can be electrical quantities such as current or voltage, or non‑electrical quantities like temperature, time, speed, or pressure, while its output consists of contact actuation or changes in circuit parameters.
When the relay’s electrical quantities—such as input voltage, current, and frequency—or non-electrical quantities—such as temperature, pressure, and rotational speed—reach their specified setpoints, the relay contacts either close or open, thereby connecting or disconnecting the circuit it controls or protects.
A relay typically consists of two main components: an input sensing element and an output actuating element. The former detects the magnitude of the input signal, while the latter either closes or opens the circuit.
Commonly used relays are contact-type, with contacts in either the closed or open state; the transition between these states is driven by a mechanical mechanism.
Voltage relay
A relay whose operation—both the contact actuation and the coil energization—is dependent on the magnitude of the voltage is called a voltage relay. It is used for voltage protection and control in electric drive systems, and when in use, its coil is connected in parallel with the load.
Characteristics: It has a large number of turns with a thin wire diameter.
Classification: Based on the type of coil current, voltage relays can be divided into AC and DC types; based on the operating voltage level, they can further be classified as overvoltage, undervoltage, and zero-voltage relays.
Intermediate relay
The function of an intermediate relay is to increase the number of controlled circuits or to enhance the contact rating, thereby enabling the distribution of control signals and power amplification.
Intermediate relays are available in both AC and DC versions. A key feature of intermediate relays is their relatively large number of contacts—typically three to four pairs or more—and they commonly employ bridge-type contacts, which are identical to those used in contactor auxiliary contacts.
Intermediate relays with higher operating power have the same structure as small contactors.
It is suitable for control circuits operating at AC voltages of 500 V or less, with coil voltages available in five options: 12 V, 36 V, 127 V, 220 V, and 380 V. The relay features eight pairs of contacts, a rated current of 5 A, and a maximum operating frequency of 1,200 operations per hour.
Suitable for control circuits with DC voltages of 110 V or less, the relay coil is available in four rated voltages: 12 V, 24 V, 48 V, and 110 V. The coil power consumption does not exceed 3 W. The relay features three normally open and three normally closed contacts with a common contact, and the contacts are rated for a current of 3 A.
Current relay
A relay whose operation is dependent on the magnitude of the current flowing through its coil is called a current relay; when in use, the coil of a current relay is connected in series with the load.
Characteristics: Its coil has few, thick turns.
Classification: Based on the type of coil current, relays can be divided into AC and DC current relays; based on the magnitude of the operating current, they can further be classified as overcurrent relays and low-current relays.
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