A Comprehensive Guide to Wiring a Relay

Learn how to wire up a relay safely and effectively with our comprehensive guide covering relay wiring diagrams in 4-pin and 5-pin configurations.

How a Relay Works

Relays operate through a process involving electromagnetism. Here's a breakdown:

Components:

• Electromagnet: A coil of wire that creates a magnetic field when electricity flows through it.
• Armature: A movable metal arm attracted to the electromagnet.
• Contacts: Electrical terminals that open or close the circuit.
• Spring: Returns the armature to its resting position when the electromagnet is off.

The Process:

• When a small current is applied to the electromagnet, it generates a magnetic field.
• This magnetic field attracts the armature, overcoming the spring tension.
• As the armature moves, it opens or closes the contacts, controlling the flow of the larger current in the second circuit.
• When the current to the electromagnet is switched off, the magnetic field collapses.
• The spring pulls the armature back, returning the contacts to their original position.

This simple yet effective mechanism allows relays to act as electrical switches controlled by a separate low-power circuit.

Connect the coil:

• Connect Pin 85 to ground (-) or the negative terminal of your power source.
• Connect Pin 86 to the positive (+) side of the control circuit, usually through a switch. This activates the electromagnet when the switch is closed.

Connect the load circuit:

• Connect Pin 30 to the positive (+) terminal of your power source. This is the common terminal.
• Connect Pin 87 to the positive (+) terminal of the device you want to control. This is the Normally Open contact.

Connect the coil:

• Connect Pin 85 to ground (-) or the negative terminal of your power source.
• Connect Pin 86 to the positive (+) side of the control circuit, usually through a switch.

Connect the load circuit:

• Connect Pin 30 to the positive (+) terminal of the device you want to control.
• Connect Pin 87 to the positive (+) terminal of your power source.

Unlike 4-pin relays, a 5-pin relay provides flexibility in controlling circuits due to its Normally Open (NO) and Normally Closed (NC) contacts. This means you can use it to turn a device ON when the relay is energised (NO) or turn a device OFF when the relay is energised (NC).

Connect the coil:

• Connect Pin 85 to ground (-) or the negative terminal of your power source.
• Connect Pin 86 to the positive (+) side of the control circuit through a switch. This activates the electromagnet when the switch is closed.

Connect the common terminal:

• Connect Pin 30 to the positive (+) terminal of your power source. This is the common terminal that provides power to either the NO or NC contact.

Choose your switching action:

• For Normally Open (NO) function: Connect Pin 87 to the positive (+) terminal of the device you want to control.
• For Normally Closed (NC) function: Connect Pin 87a to the positive (+) terminal of the device you want to control.

Relay wiring diagrams are essential tools for understanding and implementing relay circuits. They provide a visual representation of the connections between the relay, power source, switch, and load, making it easier to wire a relay correctly.

Relay Wiring Diagram Symbols

Before diving into a full diagram, it's important to familiarize yourself with the common symbols used in a relay pinout:

1. Relay: Often depicted as a rectangle with the coil and contacts represented by lines and circles. The relay pins are usually labelled with their corresponding numbers (30, 85, 86, 87, 87a).
2. Switch: Represented by a line with a break in it, indicating its ability to open and close the circuit.
3. Battery: Shown as a series of long and short parallel lines, with the longer line representing the positive (+) terminal.
4. Load: Can be symbolised by various icons depending on the device, such as a lamp for a light bulb or a motor symbol for an electric motor.
5. Wires: Represented by simple lines connecting the components.
6. Ground: Indicated by a series of decreasingly sized horizontal lines or a downward-pointing triangle.

Reading a Relay Wiring Diagram

Here are some steps to effectively read and understand a relay wiring diagram:

1. Identify the relay: Locate the relay symbol and its pin numbers. This is the central component of the diagram.
2. Trace the coil circuit: Follow the wires from the relay coil (pins 85 and 86) to the power source and the switch. This shows how the relay is activated.
3. Identify the power source: Locate the battery symbol and note its positive and negative terminals.
4. Trace the load circuit: Follow the wires from the common terminal (pin 30) to the NO (87) or NC (87a) contact, and then to the load. This illustrates how the relay controls the device.
5. Understand the switching logic: Determine whether the diagram depicts a normally open or normally closed configuration. This will tell you whether the load is activated when the relay is energised or de-energised.

Choosing the right relay wiring for your project is all about ensuring that it can handle the electrical demands of your application. Consider these factors to ensure your circuits operate reliably and safely:

• Voltage Rating: This is the maximum voltage the relay coil can handle. Always match the relay's voltage rating to your control circuit's voltage. For example, if you're using a 12V car battery to trigger the relay, choose a 12V relay.
• Current Rating: This specifies the maximum current the relay contacts can switch without damage. Ensure the relay's current rating exceeds the current drawn by the device you're controlling. If your driving lights draw 10 amps, your relay should have a rating of at least 10 amps, and ideally higher.
• Power Rating: Measured in watts, this indicates the maximum power the relay wiring can handle. Calculate the power requirement using the formula: W = V x A (Watts = Volts x Amps). If you have a 12V spotlight drawing 5 amps, the power is 60W, so your relay should have a power rating of 60W or greater.
• Application and Environment: Consider what you're using the relay for. Inductive loads like motors require relays with higher inductive load ratings to handle voltage spikes. Also, think about where the relay will be used. If it's going in your ute and exposed to the harsh Aussie sun and dust, choose a durable, weather-resistant relay.
• Australian Standards: For safety and quality assurance, look for relays that comply with relevant Australian Standards. Key standards to keep in mind include:
  • AS 60947-4-1: Deals with low-voltage switchgear and controlgear, including relays. It specifies requirements for electrical and mechanical performance, as well as safety aspects.
  • AS/NZS 3000: Known as the "Wiring Rules," this standard covers electrical installations in Australia and New Zealand. It provides guidance on the selection and installation of relays for various applications.
  • AS/NZS 61439: Specifies safety requirements for low-voltage switchgear and controlgear assemblies, which often incorporate relays.

Even with a good relay wiring diagram, mistakes can happen. Incorrect relay wiring can lead to malfunctions or even damage to your equipment. Here are some common errors and how to troubleshoot them:

• Incorrect Coil Connections: Double-check that you've connected the coil terminals (85 and 86) correctly to your control circuit. Using a multimeter, you can verify that voltage is present across the coil terminals when the switch is activated.
• Overloaded Contacts: Ensure your relay's contact rating exceeds the load current. If the contacts are overloaded, they can overheat and fail. Check the relay specifications and the current draw of your device.
• Loose Connections: Poor connections can cause intermittent operation or complete circuit failure. Make sure all relay pins have secure connections and that wires are properly crimped and insulated.
• Reversed Polarity: Connecting the power supply with reversed polarity can damage the relay and other components. Always double-check the positive (+) and negative (-) connections.

One common application of relay wiring amongst DIYers is upgrading a car’s headlights. Doing so can significantly improve their performance by taking the load off the car's original wiring to achieve brighter lights and reduce strain on the vehicle's electrical system. Here’s how it can be done:

Required Equipment

• Relay: A 12V, 40A automotive relay (or higher, depending on the headlight wattage)
• Wiring: Appropriate gauge automotive wiring for the headlight current draw (e.g., 12-14 AWG)
• Fuse holder and fuse: Rated for the headlight current draw
• Connectors: Ring terminals, spade connectors, or butt connectors as needed
• Heat shrink tubing: To insulate connections
• Tools: Wire strippers, crimping tool, electrical tape

Relay Pinout for Headlights

• Pin 85: Ground (-) - Connect to a suitable grounding point on the vehicle chassis.
• Pin 86: Switch (+) - Connect to the positive (+) wire of the original headlight wiring. This will trigger the relay when the headlights are switched on.
• Pin 30: Battery (+) - Connect directly to the positive (+) terminal of the battery through a fuse.
• Pin 87: Headlights (+) - Connect to the positive (+) wire of the new headlights.

Relay Wiring Steps

1. Mount the relay: Find a suitable location in the engine bay to mount the relay, ensuring it's secure and protected from the elements.
2. Connect the ground: Connect a wire from Pin 85 to a clean, unpainted metal surface on the vehicle chassis.
3. Connect the switch wire: Locate the positive (+) wire that powers the original headlights. Splice into this wire and connect it to Pin 86 of the relay.
4. Connect the power source: Connect a wire from Pin 30 to the positive (+) terminal of the battery. Important: Install an inline fuse holder with an appropriately rated fuse on this wire near the battery connection.
5. Connect the headlights: Connect a wire from Pin 87 to the positive (+) wire of the new headlights.
6. Test the circuit: Turn on the headlights to ensure they are working correctly. The relay should click when activated, and the headlights should be brighter than before.

When working with relay wiring in Australia, local standards can help you identify reliable and safe components.

Key standards to keep in mind include:

• AS/NZS 60947-4-1: Low-voltage switch gear and control gear
  • This standard specifically addresses electromechanical contactors and motor-starters, which include many types of relays.
  • It outlines requirements for electrical and mechanical performance, including contact ratings, operational voltages, and endurance testing.
  • It also covers important safety aspects like insulation, temperature rise limits, and protection against electric shock.
• AS/NZS 3000:2018 Electrical installations (wiring rules)
  • This is the primary standard governing electrical installations in Australia and New Zealand.
  • It provides comprehensive guidance on selecting, installing, and wiring various electrical equipment, including relays.
  • It covers aspects like wiring systems, overcurrent protection, earthing, and safety requirements for different types of installations.
• AS/NZS 61439-1: Low-voltage switch gear and control gear assemblies
  • This standard deals with the safety and performance of low-voltage switchgear and controlgear assemblies, which often incorporate relays.
  • It outlines requirements for the design, construction, and testing of these assemblies to ensure they meet safety standards.

Here are some essential safety tips for wiring a relay:

• Insulation: Ensure all connections are properly insulated to prevent short circuits and electric shock. Use heat shrink tubing or electrical tape to cover exposed wire ends and terminals.
• Grounding: Always connect the relay and any associated equipment to a proper ground connection. This provides a safe path for electrical current in case of a fault.
• Overload Protection: Protect your circuits with fuses or circuit breakers rated for the appropriate current. This will prevent damage to the relay and other components in case of an overload or short circuit.
• Disconnect Power Sources: Always disconnect the power source before working on any electrical circuit. Use insulated tools and avoid touching live wires. If you're unsure about any aspect of relay wiring, consult a qualified electrician.

By following these safety precautions and adhering to Australian standards, you can confidently tackle your relay wiring projects while minimising the risk of electrical hazards.