Beatrice Lang
Relays are electrically operated switches that are used to control one or more higher current circuits using a low current circuit. They are commonly used in automotive electrical systems and can have a variety of terminal configurations, including 4 or 5 pins. The numbers on electric relays represent the terminal numbers and are often labelled according to specific standards, such as the DIN standard (Deutsches Institut für Normung) or the NEMA standard (National Electrical Manufacturers Association). These numbers help identify the circuit schematic, voltage rating, current rating, and terminal layout, assisting with wiring and troubleshooting. However, some manufacturers may use proprietary numbering systems, and it is always recommended to refer to the product datasheet for accurate information.
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What You'll Learn
Standardisation: DIN, NEMA, and IEC
Standardisation plays a crucial role in the electrical industry, ensuring safety, performance, and compatibility. The two key organisations that set standards for the design of electric motors and associated equipment are the International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA).
IEC Standards
IEC, also known as the International Electrotechnical Commission, is a European-based organisation that sets and publishes standards for electrical and electronic technologies worldwide. IEC standards are crucial for any business aiming for a global market, influencing product development, compliance, and customer trust. IEC standards are expressed in metric units and usually result in more compact and cost-effective products. IEC motors are commonly made with cast aluminium or cast iron frames, with the conduit box mounted on top of the motor frame. IEC motors have additional designations indicating how the motor is cooled, represented by a two-digit IC code. IEC connectors are designed for versatility in international settings, allowing a wide range of devices to connect.
NEMA Standards
NEMA, the National Electrical Manufacturers Association, is a North American organisation that establishes standards for electrical equipment in North America. NEMA standards are expressed in imperial units and are known for their modularity and customisability, offering design flexibility. NEMA motors are typically made with rolled steel or cast iron frames, with the conduit box mounted on the side of the motor frame. NEMA motors have four winding insulation classes: A, B, F, and H, based on maximum temperature ratings with a reference to a 40°C ambient temperature. NEMA connectors feature specific pin configurations designed for North American voltage and current ratings, such as the NEMA 5-15 Connector with two flat parallel blades and a grounding pin.
DIN Standards
DIN standards, developed by the German Institute for Standardisation, are commonly used in Europe and play a crucial role in various industries, including automotive and electrical engineering. DIN standards cover a wide range of topics, from product specifications to testing methods, ensuring compatibility and safety. While DIN standards are not specific to electric relays, they are essential for standardising processes and products in the electrical industry.
In summary, understanding the standardisation practices of IEC, NEMA, and DIN is vital for ensuring compliance, safety, and compatibility in the electrical industry, particularly when designing and selecting electric relays and associated equipment.
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Coil pins: 85, 86, and ground and +12v
The numbers on an electric relay indicate the coil pins and their functions. Coil pins 85 and 86 are used to control the coil, while the other pins (30, 87, and 87A) switch power on a single circuit or between two circuits. The terminal numbering is based on DIN 72552, a German automotive industry standard that assigns numeric codes to electrical terminals in vehicles.
In a typical setup, coil pin 86 is connected to the positive terminal of a 12V power source, while coil pin 85 serves as the ground. This configuration is common in automotive relay systems, where the relay is used to control various electrical functions within the vehicle. The 12V power source provides the necessary voltage to energize the relay coil, allowing it to switch power on or off to the connected circuits.
It's important to note that the direction of current flow in a DC relay coil is not restricted to a specific direction. Until a diode is added, the relay can operate with either terminal being positive relative to the other. However, once a diode is introduced, the coil terminal connected to the diode's anode must be linked to the negative terminal.
The current passing through coil pins 85 and 86 is typically low, ranging from 0.16 to 0.2 amps for Bosch-style relays. This current is used to energize the relay coil, which in turn controls the flow of higher currents in the connected circuits.
Understanding the functions of coil pins 85, 86, and the associated ground and +12V connections is crucial for properly wiring and operating electric relays in various applications, especially in automotive systems.
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Switch pins: 30, 87, and 87a
The numbers on electric relay pins are standardised, with each number representing a specific function. The numbers are moulded into the plastic next to each pin and are also shown on the circuit schematic.
Switch pins 30, 87, and 87a are part of the Single Pole Double Throw (SPDT) relay system. In this system, the switch inside the relay has two positions, allowing current to flow to one of two terminals at a time. When the relay is energised, 87 and 87a change places; 87 is disconnected from 30, and 87a is connected to 30.
Pin 30 is typically connected to the battery and is known as the 'high current common' pin. It provides power to the device. Pin 87 is normally open, and pin 87a is normally closed. When the relay is not energised, terminal 87 is open, and terminal 87a is in the closed position.
It is important to note that while the numbering of DIN relay terminals is standardised, the terminal locations themselves are not completely consistent. For example, while terminals 87, 85, and 87a (on a changeover relay) are believed to always be in the same place, terminals 30 and 86 can sometimes switch places.
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Single Pole Single Throw (SPST) relays
A Single Pole Single Throw (SPST) relay is an electrically operated switch. It is an electromagnetic switch that uses an electromagnet (coil) to operate its internal mechanical switching mechanism (contacts). SPST relays are commonly used in automotive applications. They can be used to power two circuits at the same time that are normally isolated from each other, such as parking lamp circuits on German automobiles.
SPST relays typically have four terminal points: two COIL terminals, one COM terminal, and one N.O. terminal. The COIL terminals are where the voltage is placed to energize the coil. The polarity of the voltage does not matter, and a positive and negative voltage can be placed on either end. The COM terminal is the common terminal of the relay. The N.O. terminal is the Normally Open switch, where you connect the device you want the relay to power. When the COIL terminals are energised with the rated voltage, the COM and the N.O. terminals have continuity, and the device on the output is turned on. When the COIL terminals are not energised, the COM and the N.O. terminals do not have continuity, and the output is open and receives no voltage.
The coil voltage rating of an SPST relay is the voltage required for the coil to operate correctly. The switching circuit of the relay also has a voltage and ampere rating, which is the maximum rating of the switch contacts and should not be exceeded. SPST relays typically draw very little current (less than 200 milliamps) and can handle up to 30-40 amps. This allows for the switching of devices such as headlights, parking lights, and horns, which have low amperage outputs.
SPST relays are often used in automotive applications, such as glow plug relays, fuel injection relays, and timer relays. They provide benefits such as reduced cost and weight, as thinner cables can be used to connect the control switch to the relay. Relays also allow for power to be routed to a device over the shortest distance, reducing voltage loss.
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Single Pole Double Throw (SPDT) relays
Relays are electrically operated switches that control circuits and direct the flow of electricity. They are an important component in many electrical and electronic systems. One of the most common types of relays is the electromagnetic relay, which uses an electromagnet to operate a switching mechanism. When a current is applied to the electromagnet, it creates a magnetic field that moves a metal armature, opening or closing the switch.
SPDT relays typically have five pins, with terminal widths of 6.3mm. The pins are usually numbered as 30, 85, 86, 87a, and 87. When the relay is not energised, pin 30 will be connected to 87a. When energised, pin 30 connects to pin 87. It's important to note that some SPDT relays may use different numbering schemes, so it's always good to refer to the relay's schematic or diagram.
SPDT relays come in various voltage and current ratings, such as 5V, 12V, or 24V, and are designed to handle different levels of power. They are available in different shapes and sizes to suit a wide range of applications. SPDT relays can also be found in compact, space-saving designs for use in restricted spaces, such as printed circuit boards (PCBs).
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Frequently asked questions
The numbers on an electric relay refer to the terminal numbers. The terminal numbers are labelled according to a standard, such as the DIN standard, NEMA standard, or IEC standard. The DIN standard, for example, is a numbering standard for automotive electrical terminals. The NEMA standard labels terminal numbers 1-14 in the largest typical 4PDT relays, while the IEC standard uses two-digit terminal numbers, with the first digit identifying the set of contacts and the second digit identifying the terminal's purpose.
Under the NEMA standard, relays are labelled 1-14 in the largest typical 4PDT relays. The IEC standard uses two-digit terminal numbers, with the first digit identifying the set of contacts and the second digit identifying the purpose of the terminal.
In a Single Pole Single Throw (SPST) "make or break" (4-pin) relay, pins 87 and 30 are the Normally Open, Normally Closed (NO/NC) pins. Pins 85 and 86 are coil pins, while pins 30, 87, and 87a are switch pins.
Different numbering standards, such as DIN, NEMA, and IEC, provide a common language for describing, understanding, and troubleshooting relays. The DIN standard, for example, is useful for understanding the function of a relay, the socket it sits in, and the wiring of that socket.
