A glass fuse size chart helps identify common glass fuse dimensions, amp ratings, voltage ratings, fuse types, and electrical applications. Glass fuses are widely used in electronics, appliances, power supplies, control circuits, and other low-current electrical equipment.
Choosing the correct glass fuse requires more than matching its physical size. Current rating, voltage rating, breaking capacity, operating characteristic, and fuse-holder compatibility should all be checked before installing a replacement.
What Is a Glass Fuse?
A glass fuse is an electrical protection device containing a fusible metal element enclosed inside a glass cylindrical body. When excessive current flows through the circuit, the element heats up and melts, interrupting the electrical connection.
Glass fuses are commonly found in:
- Electronic equipment
- Power supplies
- Household appliances
- Audio equipment
- Control panels
- Battery chargers
- Lighting equipment
- Test instruments
- Small electrical devices
The transparent body can make visual inspection easier when the fuse element has opened.
How Does a Glass Fuse Work?
A glass fuse works by using a calibrated fusible element designed to melt when excessive current flows through it. The fuse normally carries the circuit’s operating current but opens when an abnormal current persists.
The basic process is:
- Current flows through the fuse element.
- Excessive current produces heat.
- The element reaches its melting point.
- The element separates.
- Circuit current stops.
- The protected components are disconnected.
This simple mechanism helps protect wiring and electronic components from certain overcurrent conditions.
Glass Fuse Size Chart
Glass fuses are available in several standardized physical dimensions. The following chart shows common glass fuse sizes and their typical applications.
| Glass Fuse Size | Common Current Range* | Typical Application |
|---|---|---|
| 5 × 15 mm | 0.1–5A | Small electronics |
| 5 × 20 mm | 0.05–15A | Electronics/appliances |
| 6.3 × 25 mm | 1–15A | Equipment |
| 6.3 × 30 mm | 1–20A | Electronic equipment |
| 6.3 × 32 mm | 1–20A | Power supplies |
| 10 × 25 mm | 1–20A | Equipment |
| 10 × 38 mm | 1–30A | Industrial/equipment |
Actual ratings vary by fuse design, manufacturer, voltage, breaking capacity, and operating characteristic.
Common Glass Fuse Sizes
Several glass fuse dimensions are widely encountered in electrical and electronic equipment. Among them, the 5 × 20 mm format is particularly common in many electronic and appliance applications.
Common sizes include:
- 5 × 15 mm
- 5 × 20 mm
- 6.3 × 25 mm
- 6.3 × 30 mm
- 6.3 × 32 mm
- 10 × 25 mm
- 10 × 38 mm
Always measure the original fuse and verify its complete electrical specifications before selecting a replacement.
5 × 20 mm Glass Fuse
The 5 × 20 mm glass fuse is one of the most commonly used small cylindrical fuse formats. It is widely used in electronic devices, appliances, power supplies, chargers, and control equipment.
Typical features include:
- 5 mm diameter
- 20 mm length
- Glass cylindrical body
- Metal end caps
- Fast-acting options
- Time-delay options
- Multiple current ratings
The correct amp and voltage rating must be matched to the equipment.
6.3 × 32 mm Glass Fuse
The 6.3 × 32 mm glass fuse is another common cylindrical fuse format used in electrical and electronic equipment. Its slightly larger dimensions allow it to accommodate different current ratings and construction styles.
Applications may include:
- Power supplies
- Audio equipment
- Appliances
- Control equipment
- Electronic devices
- Industrial equipment
Physical compatibility should always be checked together with electrical specifications.
6.3 × 30 mm Glass Fuse
A 6.3 × 30 mm glass fuse is used in various equipment and electronic applications where a compact cylindrical fuse is required. It may be available in different current and voltage ratings.
Before choosing this size, verify:
- Fuse length
- Fuse diameter
- Amp rating
- Voltage rating
- Fuse characteristic
- Breaking capacity
- Fuse-holder compatibility
Two fuses with similar dimensions may have completely different electrical specifications.
Glass Fuse Amp Rating
The amp rating indicates the current level associated with the fuse’s specified operating characteristics. Common glass fuse ratings range from very small electronic values to higher ratings for specialized equipment.
Common ratings include:
- 0.1A
- 0.25A
- 0.5A
- 1A
- 2A
- 3A
- 5A
- 6.3A
- 7.5A
- 10A
- 12A
- 15A
- 20A
The exact available rating depends on the fuse family and manufacturer.
Glass Fuse Voltage Rating
Voltage rating indicates the maximum circuit voltage for which a fuse is designed to interrupt current safely under specified conditions. The fuse’s voltage rating must be suitable for the circuit.
Common glass fuse voltage ratings include:
- 32V
- 125V
- 250V
- 300V
- 350V
- 500V
A fuse with the correct amp rating may still be unsuitable if its voltage rating does not meet the circuit requirement.
Glass Fuse Fast Acting vs Slow Blow
Glass fuses are commonly available in fast-acting and time-delay versions. The correct choice depends on how the protected equipment behaves during startup and normal operation.
| Fuse Type | Response | Typical Applications |
|---|---|---|
| Fast-Acting | Quick response | Electronics |
| Time-Delay | Allows temporary surges | Motors/power supplies |
| Slow-Blow | Higher surge tolerance | Transformers/equipment |
Always use the characteristic specified by the equipment manufacturer when available.
Fast-Blow Glass Fuse
A fast-blow glass fuse is designed to respond quickly to excessive current. It can be suitable for circuits containing sensitive electronic components where rapid interruption is desirable.
Common applications include:
- Electronic circuits
- Semiconductor equipment
- Control boards
- Instrumentation
- Sensitive power supplies
- Audio equipment
Fast-acting does not mean the fuse will open immediately at its rated current. Its actual time-current behavior depends on the fuse design.
Slow-Blow Glass Fuse
A slow-blow glass fuse is designed to tolerate certain temporary current surges before opening. This characteristic can be useful for equipment that draws higher current during startup.
Common applications include:
- Motors
- Transformers
- Compressors
- Power supplies
- Certain appliances
- Audio amplifiers
Using a slow-blow fuse where a fast-acting fuse is required can reduce the intended level of protection.
Glass Fuse Breaking Capacity
Breaking capacity is the maximum fault current a fuse can safely interrupt at a specified voltage and under specified conditions. It is an important consideration when selecting protection for electrical equipment.
Breaking capacity can be expressed in:
- Amperes
- Kiloamperes
- Manufacturer-specific ratings
For low-power electronics, fault currents may be relatively limited, while circuits connected to stronger power sources can require higher interrupting capability.
Glass Fuse Construction
A typical glass fuse contains a cylindrical glass tube, metal end caps, and an internal fusible element. The construction varies according to the fuse’s current rating, voltage rating, and operating characteristic.
Main components include:
- Glass body
- Fusible element
- Metal end caps
- Internal supports where applicable
- Optional filler or construction features
The transparent body can make the condition of some fuse elements easier to inspect.
Glass Fuse Color Coding
Some glass fuse systems use colored markings or bands to identify particular current ratings. However, color coding is not universal across all manufacturers and fuse standards.
For accurate identification:
- Read the printed fuse marking.
- Check the amp rating.
- Verify the voltage rating.
- Confirm fuse type.
- Check the manufacturer’s part number.
Never select a replacement based solely on color.
How to Read Glass Fuse Markings
Glass fuses often contain markings that identify important electrical specifications. These markings can be printed on the metal end cap or directly on the fuse body.
Markings may indicate:
- Current rating
- Voltage rating
- Fuse characteristic
- Breaking capacity
- Certification
- Manufacturer
- Product series
For example, 5A 250V generally identifies a fuse rated at 5 amperes and 250 volts, but additional information may be required to confirm the exact replacement.
Glass Fuse Size and Wire Size
Fuse rating and wire size should be properly coordinated. The fuse should provide suitable overcurrent protection for the conductor and connected equipment.
Consider:
- Conductor ampacity
- Wire material
- Wire length
- Insulation type
- Installation conditions
- Ambient temperature
- Circuit load
- Continuous operation
Never select a fuse simply because its rating matches the equipment’s maximum possible current.
Glass Fuse for 12V Circuits
Glass fuses are used in some low-voltage 12V equipment, including electronics, control systems, and specialized automotive or battery-powered equipment.
When selecting a fuse for 12V:
- Check normal current.
- Verify fuse voltage rating.
- Check wire capacity.
- Consider startup current.
- Verify fuse-holder compatibility.
- Check breaking capacity.
A fuse designed for one electrical system should not automatically be transferred to another voltage application.
Glass Fuse for 24V Circuits
24V systems are common in industrial control circuits, automation equipment, instrumentation, and certain electronic systems. Glass fuses can provide protection for these low-voltage circuits when properly rated.
Important considerations include:
- Operating current
- System voltage
- Fuse amp rating
- Fuse characteristic
- Cable capacity
- Breaking capacity
- Equipment requirements
Always check the fuse manufacturer’s specifications before using a particular fuse in a 24V system.
Glass Fuse for 120V Circuits
Glass fuses are used in various 120V electronic and electrical equipment. The correct fuse should match the circuit’s normal current, voltage, fault conditions, and required operating characteristic.
Before selecting a 120V glass fuse, check:
- Current rating
- Voltage rating
- Fuse type
- Breaking capacity
- Physical dimensions
- Equipment specifications
The fuse should be installed only in a suitable holder designed for the required electrical conditions.
Glass Fuse for 230V Circuits
230V equipment can use glass fuses for appliances, power supplies, control circuits, and electronic equipment. The fuse must have an appropriate voltage rating and interrupting capability for the circuit.
Important factors include:
- Operating current
- Voltage
- Inrush current
- Fuse characteristic
- Breaking capacity
- Fuse dimensions
- Holder rating
A fuse should always be selected according to the equipment manufacturer’s specified replacement requirements.
Glass Fuse for Electronics
Glass fuses are particularly common in electronic equipment because their compact construction allows them to protect sensitive components without requiring large protective devices.
Applications include:
- Televisions
- Audio equipment
- Power supplies
- Test instruments
- Chargers
- Control boards
- Electronic appliances
- Laboratory equipment
Fast-acting and time-delay options allow designers to match fuse behavior to the equipment’s electrical characteristics.
Glass Fuse for Power Supplies
Power supplies can have significant startup currents caused by input capacitors and other components. Depending on the design, a time-delay glass fuse may be used to prevent unnecessary operation during startup.
When selecting a power-supply fuse, check:
- Input voltage
- Normal input current
- Inrush current
- Fuse characteristic
- Breaking capacity
- Manufacturer specifications
The replacement fuse should match the original specification whenever possible.
How to Choose the Correct Glass Fuse
Choosing the correct glass fuse requires matching both physical and electrical specifications. A fuse that fits the holder may still be unsuitable because its current, voltage, or operating characteristics differ.
Follow these steps:
- Identify the original fuse.
- Measure its dimensions.
- Read the markings.
- Check the amp rating.
- Verify the voltage rating.
- Identify fast or time-delay operation.
- Check breaking capacity.
- Confirm holder compatibility.
- Check equipment specifications.
- Install the correct replacement.
Common Glass Fuse Sizing Mistakes
Glass fuse problems often occur when users focus only on physical dimensions or amp rating. Proper fuse selection requires checking all relevant electrical characteristics.
Avoid these mistakes:
- Installing a higher amp fuse
- Ignoring voltage rating
- Using the wrong fuse characteristic
- Ignoring breaking capacity
- Choosing by color only
- Using the wrong physical dimensions
- Bypassing the fuse
- Using an unsuitable fuse holder
- Replacing a time-delay fuse with a fast fuse without checking requirements
Also Read: Battery Cable Size Chart: Correct AWG Cable Guide
Key Points to Remember
A glass fuse size chart is useful for identifying common dimensions, current ratings, voltage ratings, and applications. However, physical size alone does not determine whether a fuse is suitable for a particular circuit.
Always remember:
- Check fuse dimensions.
- Verify current rating.
- Confirm voltage rating.
- Identify fuse type.
- Check breaking capacity.
- Match fast or time-delay operation.
- Verify fuse-holder compatibility.
- Consider inrush current.
- Follow equipment specifications.
- Never install a higher-rated fuse simply to stop repeated fuse failures.
Glass Fuse Size for Different Electrical Loads
The correct glass fuse rating depends on the equipment’s normal operating current, startup current, voltage, conductor capacity, and required fuse characteristic. Small electronic loads usually need lower-rated fuses, while larger equipment requires careful circuit-specific protection.
| Electrical Load | Common Glass Fuse Range* | Typical Fuse Type |
|---|---|---|
| LED Electronics | 0.5–3A | Fast-acting |
| Control Circuit | 0.5–5A | Fast-acting |
| Audio Equipment | 1–10A | Fast/time-delay |
| Power Supply | 1–15A | Time-delay |
| Small Appliance | 2–15A | Fast/time-delay |
| Transformer | 1–20A | Time-delay |
| Small Motor | 3–20A | Time-delay |
| Laboratory Equipment | 1–15A | Application dependent |
| Industrial Electronics | 2–30A | Application dependent |
These are general reference ranges only. Always use the fuse rating specified by the equipment manufacturer and verify voltage, breaking capacity, conductor protection, and operating characteristics.
Glass Fuse for LED Lighting
LED lighting systems normally consume relatively low current, but LED drivers can create a temporary inrush current when energized. The correct fuse therefore depends on the driver design rather than LED wattage alone.
When selecting a fuse, consider:
- Total load
- Driver input current
- Startup inrush
- Operating voltage
- Cable capacity
- Fuse characteristic
- Manufacturer specifications
A fast-acting or time-delay fuse may be suitable depending on the specific driver design.
Glass Fuse for Audio Equipment
Audio amplifiers, receivers, speakers, and related equipment often use glass fuses for internal circuit protection. Some amplifiers can draw substantial current during startup or high-power operation.
Before replacing an audio-equipment fuse, check:
- Original fuse rating
- Voltage rating
- Fuse dimensions
- Fast or slow-blow characteristic
- Equipment model
- Manufacturer specifications
Using the wrong fuse can result in repeated fuse failure or inadequate protection.
Also Read: USB Cable Size Chart: Find the Right USB Cable Size
Glass Fuse for Television
Many older televisions and some electronic displays use small cartridge fuses to protect internal power circuits. The fuse rating is normally specified by the equipment manufacturer.
When replacing a television fuse:
- Disconnect power safely.
- Locate the correct fuse.
- Read the markings.
- Match the current rating.
- Match the voltage rating.
- Match the operating characteristic.
- Check the physical size.
If the replacement fuse fails immediately, an internal equipment fault may be present.
Glass Fuse for Computer Power Supplies
Some power supplies use fuses to protect their input circuits from severe overcurrent. These fuses can be fast-acting or time-delay depending on the power-supply design.
Important specifications include:
- Input voltage
- Fuse current
- Fuse type
- Breaking capacity
- Physical size
- Safety certification
A computer power supply should not be protected by an arbitrary fuse simply because it fits physically.
Glass Fuse for Battery Chargers
Battery chargers can use fuses to protect their input or output circuits. Charger startup current and battery charging characteristics should be considered when selecting the correct fuse.
Check:
- Charger voltage
- Maximum charging current
- Input current
- Startup current
- Fuse location
- Fuse type
- Manufacturer instructions
Never bypass a charger fuse because it repeatedly opens. A fault may exist within the charger or connected battery system.
Glass Fuse for Transformers
Small transformers can use glass fuses on their primary or secondary circuits. The correct fuse depends on transformer rating, operating voltage, and expected inrush current.
For transformer protection, check:
- VA or kVA rating
- Primary voltage
- Secondary voltage
- Full-load current
- Inrush current
- Fuse characteristic
- Breaking capacity
Time-delay fuses are commonly considered for circuits where transformer energization produces temporary inrush.
Glass Fuse for Motors
Small motors can produce substantial startup current compared with their normal running current. For this reason, a time-delay glass fuse may be appropriate for certain motor circuits.
Important factors include:
- Motor rated current
- Starting current
- Operating voltage
- Motor type
- Starting method
- Fuse characteristic
- Overload protection
The fuse should be coordinated with the motor’s complete protection system.
Also Read: Transformer Wire Gauge Chart: Choose the Right AWG
Glass Fuse for Control Panels
Control panels may contain relays, contactors, PLCs, sensors, indicators, and power supplies. Glass fuses can be used to protect selected low-current control circuits.
Common considerations include:
- Control voltage
- Circuit current
- Wire size
- Component ratings
- Fuse characteristic
- Short-circuit current
- Fuse-holder compatibility
Different branches within the same control panel may require different fuse ratings.
Glass Fuse for Electronic Circuits
Electronic circuits often use small glass fuses to protect sensitive components from excessive current. Selecting the fuse requires consideration of normal operating current and the circuit’s tolerance for temporary current surges.
Applications can include:
- Circuit boards
- Test equipment
- Instrumentation
- Communication equipment
- Audio equipment
- Consumer electronics
Fast-acting fuses are often used where sensitive components require rapid overcurrent protection.
Glass Fuse Fast-Acting vs Slow-Blow
Choosing between a fast-acting and slow-blow glass fuse is essential for proper circuit protection. The correct characteristic depends on whether the circuit experiences temporary current surges during normal operation.
| Feature | Fast-Acting Fuse | Slow-Blow Fuse |
|---|---|---|
| Response | Faster | Delayed |
| Inrush tolerance | Lower | Higher |
| Electronics | Common | Application dependent |
| Motors | Less common | Often suitable |
| Transformers | Less common | Often suitable |
| Sensitive circuits | Useful | Depends on design |
The original fuse characteristic should normally be matched when replacing a fuse.
Glass Fuse Size by Current Rating
Glass fuses are available in many current ratings. Smaller electronic circuits typically use lower ratings, while specialized equipment can require larger values.
| Fuse Rating | Typical Application |
|---|---|
| 0.1A | Sensitive electronics |
| 0.25A | Control/electronic circuits |
| 0.5A | Electronics |
| 1A | Small equipment |
| 2A | Electronics |
| 3A | Control equipment |
| 5A | Appliances/equipment |
| 6.3A | Electronic equipment |
| 10A | Power equipment |
| 15A | Appliances |
| 20A | Specialized equipment |
These values are general examples and should not replace the equipment manufacturer’s specified fuse rating.
Glass Fuse Size by Voltage
Glass fuses are manufactured for different voltage levels. The fuse voltage rating must meet or exceed the requirements of the circuit under the conditions specified by the manufacturer.
| Fuse Voltage | Typical Application |
|---|---|
| 32V | Low-voltage equipment |
| 63V | Electronic systems |
| 125V | Low-voltage AC/DC |
| 250V | Household/electronic equipment |
| 300V | Specialized equipment |
| 500V | Industrial applications |
Current and voltage ratings must always be considered together when selecting a fuse.
Glass Fuse Size and Breaking Capacity
A fuse’s breaking capacity indicates how much fault current it can safely interrupt. This specification becomes particularly important when the equipment is connected to a source capable of delivering substantial short-circuit current.
Before selecting a fuse, determine:
- Available fault current
- System voltage
- Fuse interrupting rating
- Equipment requirements
- Fuse standard
A fuse should have adequate interrupting capacity for the circuit in which it is installed.
Glass Fuse Holder Compatibility
The fuse holder must be compatible with the fuse’s physical and electrical specifications. A fuse that physically fits may still be unsuitable if its current or voltage rating exceeds the holder’s capabilities.
Check:
- Fuse dimensions
- Holder dimensions
- Current rating
- Voltage rating
- Terminal arrangement
- Mounting style
- Temperature rating
A poor connection can create resistance and heat, potentially damaging the fuse holder.
Glass Fuse Color Identification
Color markings can sometimes help identify fuse ratings, but color standards vary between manufacturers and product families. Therefore, color should only be used as a secondary identification method.
For reliable identification:
- Read the fuse marking.
- Check the equipment manual.
- Verify the current rating.
- Verify the voltage rating.
- Check the manufacturer’s part number.
Never install a fuse based only on its color.
How to Test a Glass Fuse
A glass fuse can generally be tested for continuity with a suitable electrical meter after it has been safely removed from the circuit.
A basic testing process is:
- Disconnect electrical power.
- Remove the fuse safely.
- Inspect the glass body.
- Look for a broken element.
- Use a suitable continuity or resistance test.
- Compare the result with a known-good fuse if necessary.
A blown fuse should be replaced only after determining that the replacement specifications are correct.
Signs of a Blown Glass Fuse
Glass construction can make it easier to identify some blown fuses visually. However, not every failed fuse will have obvious visible damage.
Possible signs include:
- Broken internal wire
- Darkened glass
- Burn marks
- Melted element
- Discoloration
- No electrical continuity
- Equipment suddenly losing power
A meter test is often more reliable than visual inspection alone.
Why Does a Glass Fuse Keep Blowing?
Repeated fuse failure generally indicates that excessive current is still present in the circuit. Replacing the fuse repeatedly without finding the cause can leave the underlying fault unresolved.
Common causes include:
- Circuit overload
- Short circuit
- Faulty component
- Damaged wiring
- Excessive startup current
- Incorrect fuse characteristic
- Incorrect fuse rating
- Power-supply failure
- Motor or transformer fault
Investigate the cause before installing another replacement fuse.
Can You Replace a Glass Fuse With a Ceramic Fuse?
A glass fuse should not automatically be replaced with a ceramic fuse simply because the dimensions appear identical. Fuse construction, breaking capacity, voltage rating, and operating characteristics can differ.
Before substituting a fuse, verify:
- Current rating
- Voltage rating
- Fuse characteristic
- Breaking capacity
- Dimensions
- Fuse standard
- Manufacturer approval
If the equipment specifies a particular fuse type, use that type.
How to Choose the Correct Glass Fuse
The correct glass fuse should match the equipment and circuit requirements in every important respect. Physical dimensions are only one part of the selection process.
Follow these steps:
- Identify the original fuse.
- Read all markings.
- Measure the dimensions.
- Determine the circuit voltage.
- Confirm the amp rating.
- Identify fast or slow-blow operation.
- Verify breaking capacity.
- Check the fuse holder.
- Follow manufacturer specifications.
- Install only the correct replacement.
Common Glass Fuse Replacement Mistakes
Incorrect fuse replacement can reduce circuit protection and potentially damage equipment. The most common mistake is selecting a fuse based only on physical fit.
Avoid:
- Using a higher amp fuse
- Ignoring voltage rating
- Ignoring breaking capacity
- Using fast-blow instead of slow-blow
- Using slow-blow instead of fast-blow
- Choosing by color
- Using an incorrect physical size
- Bypassing the fuse
- Installing a damaged fuse
- Ignoring the equipment manufacturer’s specifications
Glass Fuse Maintenance and Inspection
Glass fuses generally do not require extensive routine maintenance, but fuse holders and electrical connections should be inspected periodically in equipment where reliability is important.
Check for:
- Loose fuse holders
- Discoloration
- Overheating
- Corrosion
- Damaged terminals
- Broken clips
- Incorrect fuse ratings
- Signs of arcing
- Physical damage
Any maintenance involving electrical equipment should be performed using appropriate safety procedures.
FAQs:
What is the most common glass fuse size?
The 5 × 20 mm glass fuse is one of the most commonly encountered cylindrical fuse formats, particularly in electronic equipment, appliances, power supplies, and control circuits. It is available in many current ratings and both fast-acting and time-delay versions.
What does 5 × 20 mm mean on a glass fuse?
5 × 20 mm refers to the approximate physical dimensions of the fuse: 5 mm in diameter and 20 mm in length. This identifies the physical format but does not specify the fuse’s current, voltage, or operating characteristic.
How do I know what size glass fuse I need?
Check the original fuse markings, physical dimensions, equipment manual, current rating, voltage rating, and fuse characteristic. The replacement should match the manufacturer’s specified requirements rather than being selected by physical size alone.
Can I use a higher amp glass fuse?
No, a higher amp fuse should not be installed simply because the original fuse keeps blowing. A higher rating can allow excessive current to flow through wiring or components and may reduce the intended level of circuit protection.
What is the difference between fast-blow and slow-blow glass fuses?
A fast-blow fuse responds more quickly to excessive current, while a slow-blow fuse allows certain temporary current surges before opening. Fast fuses are often used for sensitive electronics, while time-delay types can suit motors and transformers.
Final Thoughts
A glass fuse size chart is useful for identifying common fuse dimensions, current ratings, voltage ratings, and applications. However, the correct replacement depends on the complete electrical specifications of the circuit and equipment.
Before replacing a glass fuse:
- Check the physical dimensions.
- Match the current rating.
- Verify the voltage rating.
- Identify the fuse characteristic.
- Check breaking capacity.
- Confirm fuse-holder compatibility.
- Consider startup or inrush current.
- Follow equipment specifications.
- Never install a higher-rated fuse without proper electrical evaluation.
Using the correct glass fuse helps maintain reliable overcurrent protection and reduces the risk of damage caused by electrical faults.