- Published 10 Dec 2024
- Last Modified 10 Dec 2024
- 10 min
Fuse Types, Sizes and Uses: A Comprehensive Guide
Discover different types of fuses, what they do in a circuit, and the various sizes available.
What is a Fuse?
A fuse is a small but crucial safety device that protects electrical circuits and devices from damage caused by excessive current flow. It acts as a sacrificial link, designed to melt and interrupt the circuit when the current surpasses a safe level.
Fuses are essential in modern electronics, safeguarding everything from household appliances and industrial machinery to delicate electronic components in smartphones and computers.
What Does a Fuse Do in a Circuit?
A fuse acts as a safety valve for electrical circuits, limiting the current flow. This mechanism protects components from damage should an overcurrent occur.
Working Mechanism of A Fuse
A fuse typically involves a metal wire or filament enclosed within a ceramic or glass body. This filament is carefully calibrated to melt at a specific temperature corresponding to a particular current rating.
Fuses are connected in series within a circuit, meaning all the current flowing through the circuit must pass through the fuse. If the current exceeds the fuse's rating, the filament heats up and melts, breaking the circuit and stopping the flow of electricity. This interrupted flow prevents damage to other components in the circuit.
Once a fuse has blown, it must be replaced with a new one of the same rating to restore circuit functionality.
Melting Point and Current Rating
The melting point of the fuse filament determines the current rating of the fuse. The current rating, expressed in amperes (A), indicates the maximum current the fuse can carry continuously without melting.
Various fuse types are available in a wide range of current ratings to accommodate different load capacities. Therefore, choosing the correct current rating is crucial to ensure adequate circuit protection. For example, a fuse with a current rating that is too high may not blow when needed, while a fuse with a rating that is too low may blow prematurely, disrupting regular operation.
What Causes a Fuse to Blow?
When a fuse "blows," it means that the fuse filament has melted due to excessive current flow, interrupting the circuit. For example, if a 10A fuse is subjected to a 15A current, it will blow, stopping the current flow and protecting the circuit from potential damage. Here are some common causes of a blown fuse:
- Overloading: Connecting too many devices to a single circuit can exceed the circuit's capacity, causing the current to rise above the fuse's rating.
- Short circuit: A short circuit occurs when a low-resistance path is created in the circuit, allowing a large current to flow. This can happen due to damaged insulation, faulty wiring, or component failure.
- Faulty wiring: Incorrect or damaged wiring can lead to increased resistance in the circuit, causing the current to rise and potentially blow the fuse.
- Wrong fuse type: An incorrect fuse type, such as a fast-acting fuse in a circuit requiring a slow-blow fuse, can lead to premature fuse failure.
Types of Fuses
There are different electrical fuse types for various applications in Australia. Selecting the correct fuse is crucial to ensure optimal circuit protection and reliable operation of electrical systems. Read on for a breakdown of common fuse categories.
Cartridge Fuses
Cartridge fuses are one of the most general-purpose types of fuses. They can be made from various materials, such as glass, ceramic, and porcelain. The internal resistor wire is typically made from copper, silver, aluminium, or zinc.
Applications: Cartridge fuses are widely used in residential and commercial settings to protect lighting circuits, appliances, and other electrical equipment. A cartridge fuse offers reliable overcurrent protection like a type B circuit breaker.
Key Characteristics:
- Shape: Cylindrical, with metal contacts at both ends. This design makes them easy to replace.
- Variety: These fuses are available in a wide range of current ratings and sizes, from smaller ferrule fuses with a 60-amp rating to larger knife-blade cartridges with a 600-amp rating.
Resettable Fuses (PTCs)
Resettable fuses, or polymeric positive temperature coefficient (PTC) devices, can reset themselves after tripping. These fuses contain a special type of polymer material that increases resistance when heated, interrupting the current flow. Once the fault is cleared and the fuse cools down, its resistance decreases, and the circuit is restored.
Applications: Resettable fuses are commonly used in cases where an automatic reset is desirable, such as consumer electronics, telecommunications, and automotives.
Key Characteristics:
- Reusable: Due to the self-resetting functionality of these fuses, they’re more cost-effective over long-term circuit protection.
- Variety: Resettable fuses are available as both surface mount (SMD) and wire-ended fuses.
Non-Resettable Fuses
Non-resettable fuses, as the name suggests, need to be replaced once they have blown. These single-use fuses offer a simple and reliable form of circuit protection, and are designed to be mounted directly onto a printed circuit board (PCB).
Applications: Non-resettable fuses are widely used in applications like power supplies, appliances, and industrial machinery. They are often used in situations where a visual indication of a fault is required, as the blown fuse clearly indicates that something has caused an overcurrent condition.
Key Characteristics:
- Simple and cost-effective: Non-resettable fuses are simple in design and relatively inexpensive, making them a cost-effective solution for basic circuit protection.
- Wide range of ratings: With various current ratings and sizes, these fuses are suitable for applications across low-power electronics to high-power industrial circuits.
Bottle Fuses
Bottle fuses, also known as diazed fuses, have a distinctive bottle-shaped design with a threaded base. What this design does is that it ensures that the wrong fuse is never inserted into the wrong circuit, offering robust protection against overcurrents and short circuits.
Applications: Bottle fuses are often found in light industrial applications, such as PLC and CNC control panels.
Key Characteristics:
- Bottle-shaped design: The unique bottle shape with a threaded base ensures secure installation and prevents accidental loosening due to vibrations or other mechanical disturbances.
- High breaking capacity: Bottle fuses have a high breaking capacity, allowing them to safely interrupt large fault currents without shattering or causing damage to the fuse holder.
Car Fuses
Car fuses are specifically designed to protect the various electrical circuits and components in automobiles. Different types of fuses for cars exist, including blade fuses, cartridge fuses, and mini fuses, each with its specific applications and current ratings.
Applications: Car fuses are essential for protecting the electrical systems in vehicles, safeguarding everything from lighting and entertainment systems to engine management and safety features.
Key Characteristics:
- Compact size: Many car fuses are available in small sizes, from the smallest Micro2 to the largest Maxi size, to accommodate various applications..
- Identification: Fuses are colour-coded by size, with the amp rating displayed on top.
Square Body Fuses
Square body fuses are reliable and quick-acting fuses. They feature a threaded hole through the centre of their casing, enabling them to be conveniently screwed into place without the need for special fuse holders.
Applications: Square body fuses are often found in high-power applications, such as industrial control panels, where space is limited and reliable overcurrent protection is required.
Key Characteristics:
- Compact shape and size: The square shape allows for efficient use of space, making them ideal for applications where miniaturisation is important.
- Suitability for high-current applications: Square body fuses are available in high current ratings, making them suitable for protecting power circuits and industrial equipment.
Tag Fuses
Tag fuses have metal tags protruding from the fuse body, providing convenient connection points for installation. There are various types of tag fuses, such as bolted, centred, hole mounted, offset, and slotted options.
Applications: Tag fuses are designed for general industrial applications including power distribution, motor protection, and cable protection. The protruding tags allow for easy installation and removal, even in tight spaces or when wearing gloves.
Key Characteristics:
- Ease of use: The metal tags provide convenient gripping points for easy installation and removal.
- High breaking capacity: Tag fuses are designed to handle high fault currents, making them suitable for harsh industrial environments.
Thermal Fuses
Thermal fuses are temperature-sensitive devices designed to protect equipment from overheating. They have two ratings – a holding temperature rating and a functioning temperature rating. The former refers to the temperature range in which the fuse will hold without blowing, while the latter indicates the lowest temperature that will cause the fuse to blow.
Applications: Thermal fuses are commonly used in domestic appliances that produce heat, such as coffee makers, hair dryers, and tumble dryers. They help to prevent overheating and potential fire hazards.
Key Characteristics:
- Temperature-sensitive operation: Thermal fuses operate based on temperature rather than current, making them ideal for protecting against overheating caused by various factors, such as blocked airflow or component failure.
- Compact shape and size: These fuses are typically small and self-contained, making them easy to integrate into various devices and applications.
About Fuse Sizes
Selecting the correct fuse type and size is crucial for ensuring the safe and reliable operation of electrical systems. A fuse that is too large may not blow during an overload, potentially leading to equipment damage or fire hazards. Conversely, a fuse that is too small may blow prematurely, causing unnecessary disruptions to normal operations. The load and electrical demand of your electrical system will help to determine the required fuse size.
On top of the electrical requirements, it’s essential to select a fuse that fits the physical demands of the intended application. For example, fuses for higher voltage systems tend to be larger to accommodate the increased insulation requirements. Use the current and voltage ratings to identify the required physical dimensions of the fuse.
Size and dimensions of common fuse types
Common fuse sizes in Australia range from 5A to 40A for residential and automotive applications, and 10A to over 100A for industrial applications. The table below provides a more comprehensive overview of various sizes and dimensions for different fuse types:
Type | Size | Dimensions | Current Rating | Application |
|---|---|---|---|---|
Cartridge Fuses | Small | Length: 20mm, Diameter: 5mm | 0.5A to 5A | Household appliances |
Cartridge Fuses | Medium | Length: 32mm, Diameter: 10mm | 5A to 30A | Industrial systems |
Cartridge Fuses | Large | Length: 63mm, Diameter: 15mm | 30A to 100A+ | High-power circuits |
Blade Fuses | Micro | Length: 10mm, Width: 3.5mm | 1A to 15A | Low-power circuits (automotive) |
Blade Fuses | Standard | Length: 20mm, Width: 8mm | 5A to 30A | Automotive applications |
Blade Fuses | Maxi | Length: 38mm, Width: 10mm | 30A to 100A+ | High-current circuits (automotive) |
Glass Tube Fuses | Standard | Length: 20mm, Diameter: 5mm | 0.5A to 10A | Household and electronic devices |
Thermal Fuses | Standard | Length: 10mm, Diameter: 4mm | 0.5A to 10A | Appliances (toasters, irons, etc.) |
Australian Electrical Standards for Fuses (AS/NZS 60269)
Ensuring the safety of electrical systems is paramount, and selecting fuses that adhere to relevant standards is crucial. In Australia, the AS/NZS 60269 standard plays a vital role in regulating low-voltage fuses.
This standard specifies the requirements for fuses used in various electrical applications, ensuring their safety and performance.
The AS/NZS 60269 forms part of a series of international standards aligned with the IEC 60269 series, but is tailored to meet the specific needs of Australia and New Zealand.
Fuses used in equipment or installations must comply with AS/NZS 60269 standards in these areas:
- Third-party testing and certification: Fuses may have to undergo testing and certification by independent organisations to demonstrate that they meet the specified performance criteria, such as current-carrying capacity, interrupting rating, and temperature rise.
- Marking requirements: Fuses must be clearly marked with relevant information, including the fuse type, current rating, voltage rating, and manufacturer's details. This helps users identify and select the correct fuse for their application.
