Fuses are vital safety components in electrical systems, primarily used to protect equipment from current overloads and short circuits. When a fuse blows, it cuts off the current, thus preventing a more serious fault or fire. In RVs, vans, and boats, properly functioning fuses ensure the smooth use of all types of electrical equipment. Therefore, knowing how to tell if a fuse is blown is an important skill for every caravan or boat owner. In this article, we will cover the symptoms of recognising a blown fuse, how to check and confirm the fuse status, and the necessary maintenance measures.
What is a Fuse
A fuse is an overload protection device that can blow if the current exceeds its rated value. It is usually manufactured from a metallic material with a specific melting point. During normal operation, current passes through the fuse, but when the current is too high, the metal melts due to the heat generated, breaking the circuit.
Common fuse types and their ratings
Fuses play an important protective role in the electrical systems of RVs (motorhomes), vans and boats. Understanding the different types of fuses and their ratings can help you make better judgements and perform better maintenance. Here are some common fuse types and their characteristics:
1. Glass Tube Fuse
Description: round glass casing with metal wires inside.
Rating: Common ratings range from 1 amp to 30 amps. Ratings are usually identified by colour coding:
- 1A - Silver
- 2A - red
- 3A - Brown
- 4A - Blue
- 5A - Green
- 7.5A - Yellow
- 10A - Orange
- 15A - Light Blue
- 20A - Coral Colour
- 25A - Purple
- 30A - Dark Blue
2. Automotive Specialised Fuses (ATO/ATC)
Description: Plastic casing with two metal contacts at the bottom, typically used in automotive and heavy duty vehicle electrical systems.
Ratings: from 5 amps to 30 amps, designed for automotive electrical equipment, colour coded as follows:
- 5A - Green
- 10A - Blue
- 15A - Dark Orange
- 20A - Red
- 25A - Yellow
- 30A - Grey
3. Fast blow fuses
Description: Designed to blow quickly to protect electronic equipment, typically used in high power circuits.
Ratings: Ranging from 1 Amp to 40 Amps, specifically designed for high power equipment, specifications and colour coding may vary by manufacturer.
4. Mini Fuses
Description: A smaller ATO fuse suitable for modern miniature electrical systems.
Ratings: from 5 amps to 30 amps, colour coded as standard automotive fuses.
5. Time Delay Fuses
Description: Used in circuits where a high current is required for a short period of time when the equipment is started, e.g. electric motors, this fuse allows a short period of overload.
Ratings: Common range from 1 amp to 30 amps.
Causes of blown fuses
The main causes of blown fuses include the following:
- Overloading: this is when the current in the circuit exceeds the rated current of the fuse. When the load is too heavy or the equipment malfunctions, it may cause the current in the circuit to rise abnormally, making the fuse stay hot for a long time and eventually blow. For example, in household electricity consumption, the simultaneous use of several high-power electrical appliances (e.g., air conditioners, heaters, etc.) may cause the circuit to be overloaded, which in turn triggers the fuse to blow.
- Short Circuit: When two conductors in a circuit are connected out of order, resulting in the current bypassing the device itself and flowing directly through the wires, the current will increase rapidly, causing the fuse to blow. Short circuits can be caused by old wiring, damaged insulation, and incorrect wiring. Short circuit faults are more common in both home circuits and vehicle electrical systems.
- Excessive Temperature: A fuse may also fail if the ambient temperature in the circuit is too high, beyond the temperature rating that the fuse can withstand. At high temperatures, the conductor material inside the fuse may deteriorate faster, reducing its ability to withstand the current, which can cause it to blow.
- Excessive Voltage: Fuses may also blow when the supply voltage exceeds the rated voltage that the fuse can withstand. Excessive voltage can be caused by fluctuations in grid voltage, equipment failure, or improper operation.
- Installation or Damage Problems: When installing a fuse, if the screws are not tightened or the fuse itself is damaged, it may also cause the fuse to blow. In addition, poor contact between the fuse and the plug screws may also cause ignition and heat, causing the screws holding the fuse to oxidise and ‘burn out’, thus triggering the fuse to blow.
Recognising the symptoms of a blown fuse
Electrical equipment not working properly
If you notice that certain electrical equipment in your RV, van or boat isn't working properly, such as lights going out or no power coming from an outlet, this could be a sign of a blown fuse.
Smells bad or burns
In some cases, the electrical system may cause an odour or burning smell. In this case, you need to check the status of the fuse immediately to avoid a potential fire risk.
Changes in the appearance of the fuse
Check the appearance of the fuse itself. If the colour of the fuse is darkened, or there are obvious signs of blowing
Check and verify fuse status
Preparing Tools
In order to check the fuses, you need to prepare some tools, including a fuse extractor and a multimeter. The fuse extractor will help you remove the fuse smoothly, while the multimeter can be used to check the conductivity.
Locate the fuse box
In an RV, van or boat, the fuse box is usually located near the electrical control panel. Consulting the owner's manual can help you locate it quickly.
Remove and check fuses correctly
Carefully remove the fuse using a fuse extractor to check the integrity of the fuse. If visual inspection does not confirm this, you can use a multimeter to check conductivity. Set the multimeter to resistance mode and touch both ends. If it shows zero, the fuse is normal; if it shows infinity, the fuse is blown.
Dealing with blown fuses
Replace the fuse:
Selecting the right fuse with the right current rating: before replacing a fuse, make sure you select a spare fuse that matches the type and current rating of the blown fuse. Do not use a fuse with a current rating that is too high or too low, as this may result in inadequate circuit protection or frequent fuse blowing.
Proper Installation: Use a fuse puller to remove the blown fuse from the fuse box. Then, insert the spare fuse into the appropriate slot, making sure it is securely fastened in place.
Temporary solution (not recommended for long-term use):
If a spare fuse is not available and you urgently need to restore circuit functionality, consider using a length of wire of appropriate diameter and length (e.g. copper) as a temporary alternative. However, please note that this method poses a significant safety risk as the wire may not provide sufficient current protection. Therefore, please buy and replace the fuse with a suitable one as soon as possible.
Troubleshooting:
Before replacing a fuse, be sure to check for possible causes of a blown fuse. Common faults include short circuits, overloaded equipment, or poor wiring. If the cause of the fault cannot be determined, consult a service professional.
Fuse replacement procedure
1. Select the right fuse
- Confirm type and rating: Before replacing a fuse, make sure you have a spare fuse that matches the blown fuse. Check the label of the original fuse or the user's manual and select a fuse of the same type (e.g. ATO, glass tube, etc.) and current rating (e.g. 10A, 15A, etc.).
- Pay attention to safety: Never use a fuse with too high or too low a current rating, as this may result in a failure of circuit protection or frequent blowing of the fuse.
2. Handling of blown fuses
- Disconnect the power supply: Before replacing a fuse, always disconnect the power supply to the relevant circuit, this can usually be done by switching off the switch or disconnecting the battery.
- Remove the blown fuse: Use a fuse puller (or carefully pull it out manually) to remove the blown fuse from the fuse box, taking care not to hurt your fingers.
3. Installing a New Fuse
- Insert the spare fuse: Insert the spare fuse into the appropriate slot, making sure that it is firmly seated and that the contacts are making good contact. Check that it is correctly positioned and orientated.
4. Check and restore power
- Restore power: After completing the fuse replacement, reconnect the power supply and switch it on.
- Test the equipment: Check whether the corresponding electrical appliances or equipment work normally, and confirm that the fuse replacement is successful.
Quick Guide: Replacing a fuse in your Airstream | Easy steps
Measures to prevent fuse blowing
Regular inspection of the electrical system
Regularly checking the electrical system to ensure that all connections and equipment are functioning properly can effectively reduce the risk of blown fuses.
Use electrical appliances appropriately to avoid overloading
Ensure that you do not use a large number of electrical appliances at the same time to avoid overloading the current. Establish a sensible habit of using electrical appliances, especially when travelling or camping for long distances.
Installation of Protective Devices
Consider adding protective devices such as circuit breakers to your electrical system to better prevent overloading.
Use high-quality fuses
Emphasise the importance of using standard-compliant fuses. When buying, choose reputable brands and manufacturers to ensure the quality and reliability of your fuses.
FAQs
Is it possible to replace a blown fuse?
No, it is not possible. When a fuse blows, you should replace it with a fuse that is appropriate for the size of the blown fuse, and avoid using a fuse that is of poor quality or does not meet the specifications.
Does a blown fuse mean that there is a fault in the circuit?
Not necessarily. A blown fuse may be caused by overloading or short-circuiting of the circuit, but it may also be caused by a faulty fuse or improper installation. Therefore, the circuit should be inspected after replacing the fuse to determine if there are any other points of failure.
What should I do if I don't have a spare fuse?
Try to avoid using unsuitable alternatives such as metal wires as this may lead to serious safety hazards. If a spare fuse is not available, it is advisable to temporarily disconnect the appliance until a suitable type of fuse can be bought. Be sure not to use unsuitable alternatives to restore the circuit for a long period of time.
Conclusion
Fuses play an integral role in the electrical systems of RVs, vans and boats. Regular inspection and maintenance of fuses and related appliances will ensure that your equipment operates safely and avoids potential risks. Hopefully, this article has helped you better understand how to determine and deal with blown fuses.
