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How to Wire 14-PIN Relay for Holding or Latching Circuit?

Wiring Diagram of Holding / Latching Circuit using 14-Pins PLA Relay 

In the realm of electrical and electronic systems, relays play a crucial role in controlling various devices and processes. A holding circuit, built using a 14-pin relay, is a fundamental component that aids in maintaining the state of a relay’s contacts after the initial triggering signal has ceased. This article explores the concept of a holding circuit, the intricacies of a 14-pin relay, its working principle, applications, and practical considerations.

What is a 14-Pin Relay

A 14-pin relay ((also known as 4C/O Relay i.e. 4 commons and outputs) is a versatile electromechanical device that consists of 14 pins arranged in a specific configuration. These pins serve different purposes and are essential for establishing connections with the external circuitry. Here’s a breakdown of the pins and their functions:

  1. Coil Pins: These are the pins responsible for providing the electrical current necessary to energize the relay coil. Generally labeled as A1 or 13 and A2 or 14 or similar designations, these pins create the magnetic field that controls the switching of the relay contacts.
  2. Common (C) Pins: The common pins are the central connections that are linked to the relay’s moving contacts. They are connected to the normally open (NO) and normally closed (NC) contacts when the relay is in the unenergized state.
  3. Normally Open (NO) Pin: This pin is connected to the common pin when the relay coil is energized, thus completing the circuit.
  4. Normally Closed (NC) Pin: This pin is connected to the common pin when the relay coil is not energized. It opens when the relay coil is activated.
  5. Other Pins: Depending on the specific design and features of the 14-pin relay, there might be additional pins for functions like coil suppression, diode protection, and indicator LEDs.

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Connections of 14-Pin Relay Terminals:

As shown in fig below, the 14-pin relay terminals are interconnected with the following pin configuration:

  • Pins 13, 14: Relay’s Coil Connections ( L or + and N or – = energizing the coil)
  • Pin Common (COM) 9 is normally closed (NC) with 1 and Normally Open (NO) with 5.
  • Pin Common (COM) 10 is normally closed (NC) with 2 and Normally Open (NO) with 6.
  • Pin Common (COM) 11 is normally closed (NC) with 3 and Normally Open (NO) with 7.
  • Pin Common (COM) 12 is normally closed (NC) with 4 and Normally Open (NO) with 8.

14-PIN PLA Relay - Base, Socket & Terminals Connections

Understanding Holding Circuits and Their Importance

Holding circuits, also known as latching circuits or latch relays, are designed to maintain the relay contacts in a specific state even after the original input signal is removed. This feature is advantageous in scenarios where sustained control is required, such as in power distribution, motor control, automation, and industrial processes.

The holding circuit allows the relay to “remember” its last position, reducing the dependency on continuous power input to keep the relay activated. This contributes to energy efficiency and ensures that the circuit remains in its intended state without requiring a constant signal.

Latching / Holding Circuit Using 14-PIN PLA Relay

Below is the step-by-step tutorial to wire a latching or holding circuit using 14-pin relay according to the given wiring diagram.

How to Wire a 14-PIN Relay Latching - Holding Circuit

  • Connect the phase wire from the two-poles MCB (100-230V AC breaker) to the 14 terminal of the relay.
  • Similarly, wire the neutral wire from the MCB to the 13 terminal of the relay.
  • Connect two pushbuttons (NC and NO) in series with the phase wire from the CB to the relay’s terminals 14.
  • Connect a direct wire from the phase (from MCB and right before the pushbuttons) to the 10, 11 and 12 terminals of the relay.
  • Connect a holding wire from the 2nd terminal of NC (or starting terminal of NO pushbutton) to the 5 terminal of the relay.
  • Connect a Jumper wire from right after the NO (Green pushbutton) to the 9 terminal of relay.
  • Finally, connect the output wires from 6, 7 and 8  terminals of the relay to the three (Red, Green, Blue) light bulbs.
  • Lastly, connect the neutral and ground/earth wire to all three light bulb holders. The circuit is complete.

Working Principle of a Holding Circuit with a 14-Pin Relay

The functioning of a holding circuit built using a 14-pin relay involves two distinct states: set and reset. Let’s dive into the step-by-step process:

1. Set State (Latch On)

  1. Apply a momentary electrical pulse (by pressing the Start – NO push button across the coil pins (13 and 14 (A1 & A2)). This pulse energizes the coil and generates a magnetic field.
  2. The magnetic field causes the relay’s switching mechanism to change its position. The common (C) pins are now connected from the normally closed (NC) pins to the normally open (NO) pins, completing the circuit in that configuration.
  3. Once the coil is energized, it “latches” into this state, even if the original pulse is removed. The holding circuit is now activated. This because the jumper as holding wire is connected from the input of NO (green pushbutton) to the 5 terminal of relay and direct supply from CB to the 10, 11 and 12 terminals of relay.

2. Reset State (Latch Off)

  1. To return the relay to its original state, apply a momentary electrical pulse (by pressing the Stop – NC pushbutton) with reversed polarity across the coil pins (A2 and A1 (terminal 13 and 14).
  2. This reversed pulse de-energizes the coil, disrupting the magnetic field.
  3. As a result, the switching mechanism returns to its initial position. The common (C) pins are now connected back from Normally open (NO) to the normally closed (NC) pin just like before the operation.
  4. The relay remains in this state until a new pulse is applied, which brings it back to the set state.

Applications of Holding Circuit

Holding circuits built with 14-pin relays find applications in various domains due to their ability to maintain states without continuous power supply. Some common applications include:

  1. Motor Control: Holding circuits are employed to control the direction of rotation in motors, allowing for forward and reverse motion without sustained input.
  2. Power Distribution: Holding circuits are used in power distribution systems to maintain the position of circuit breakers, ensuring the stability and safety of the electrical grid.
  3. Industrial Automation: Holding circuits play a crucial role in controlling machines, conveyors, and robotic systems, allowing them to stay in their operational states.
  4. Lighting Systems: These circuits are used to control lighting systems, such as emergency lighting, where maintaining illumination is essential.
  5. HVAC Systems: Holding circuits are used to control the operation of heating, ventilation, and air conditioning systems.

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