Generator Keeps Blowing Fuse: Likely Causes

A generator that is blowing fuses indicates an underlying issue and should not be ignored. You need to understand the primary reasons this happens and how to troubleshoot it.

Likely causes of a generator repeatedly blowing a fuse include:

• An electric current overload
• Short circuit in the system
• Ground fault.
• Incorrect fuse size installed

Any of these will lead to an abnormal flow of electricity, which will melt the wire ribbon in the fuse and break the circuit instantly.

I realize how frustrating it can be when a fuse keeps blowing. People who have standby generators such as Generac complain of this issue often. Let’s see what we can do to solve this.

Troubleshooting A Generator That Keeps Blowing A Fuse

One of the key distinctions that you need to determine is this: does the fuse blow only when there is a load on it or does the fuse blow even with no load?

Clarifying this will help you to determine where the problem lies.

If the fuse only blows when the generator is carrying a load, you are likely facing an overload issue. You may simply need to back off of the load that the generator is trying to pull.

To understand the causes of a blown fuse, let’s go through the basics of fuses. We’ll also look at how a fuse works, outline the types of fuses, and finally explain in detail the causes. This will help you to understand why the fuse is blowing and how to solve the problem.

What Is a Fuse? 

A fuse is a protective device added to a circuit to act as the weak link and prevent current overload. 

Fuses unsure excess current does not pass through a circuit and destroy appliances attached to it. By preventing overcurrent, fuses also protect the circuit wires from starting a fire in case of an electrical fault.

So what is a fuse made of exactly? 

This device comprises an element made of a metal ribbon, thin wire, or spring enclosed in a non-combustible encasing and mounted in series between a pair of electrical terminals.

A fuse can be made of a variety of metals, e.g., copper, aluminum, zinc, or silver.

Fuses are found in various electrical systems, including the following:

• Vehicles and motorcycles
• Generators
• Electrical cabling in homes
• Mobile phones and laptops
• Power transformers
• Electrical appliances like TVs, ACs, washing machines, and music systems

The main use of a fuse is to create an open circuit when excessive current flows through the system hence preventing damage to the system and its electrical components. Here is a list of the functions played by fuses:

• Prevents short circuit. When an unintended contact between electrical components, e.g, wires of a circuit results in diversion of the current, a lower resistance than that of a normal circuit may form. This can cause overheating or even a fire. Fuses work in such situations to disconnect the circuit and prevent the damage from occurring. 
• Prevent damage to electrical devices in case of faulty circuit operation.
• Prevents overload of an electrical circuit. If too many appliances are connected to the same circuit, it may lead to overload beyond what the circuit can bear. A fuse or circuit breaker connected to such a circuit will break the circuit to prevent the overload.
• Acts as a barrier between faulty circuits and humans. Faulty circuits can lead to electrical fires or explosions and cause harm to whoever is nearby. Fuses prevent this by breaking the circuit before damage occurs. 

How Fuses Work

As we’ve already mentioned, fuses are fitted in series in the circuit they are meant to protect. This is so that all the current flowing through the circuit goes through the fuse to ensure it’s within the capacity that the circuit and appliances can safely handle.

The fuse size used for each circuit should match the gauge of the circuit wires. Once current starts flowing, it first goes through the fuse. If it exceeds the current-carrying capacity of the fuse, the metal element overheats and eventually melts. This immediately interrupts the current and breaks the circuit.

This means that the fuse is made in such a way that it easily melts immediately. It detects an over-current. So fuses blow before the circuit wires themselves can overheat, get damaged, or even possibly cause a fire. 

Once a fuse blows, it cannot be reset, as is the case with circuit breakers. A blown fuse has to be unplugged and replaced. The replacement fuse needs to be correctly matched to the circuit’s amperage. 

Types of Fuses and Sizing

There are different types of fuses. Here are some of the most common:

Type-T Fuses

These are also known as the Edison base fuses. 

This is the standard fuse for 120/125-volt circuits. It can be used in a household cabling system. The ampere rating is no more than 30 amps, and you’ll see this printed on the face of the fuse. 

The reason the amperage rating is always clearly displayed is to avoid someone replacing their fuse with the wrong fuse size. The biggest concern is “over-fusing,” i.e, installing a fuse that’s larger than the circuit’s ampere rating. Over-fusing will allow excess current that’s beyond what the circuit can handle and so can lead to damage. 

Type-S Fuses

Type-S fuses consist of a base and the fuse itself. 

The base is a socket adapter for the fuse, and its size varies with the fuse amperage. This feature safeguards from mismatching fuses.

Type-S fuses are, therefore, a great choice, where practical, since it prevents the installation of the wrong fuse size in the future.

Cartridge Fuses

Cartridge fuses are used in 240-volt circuits. They can either be used for appliance circuits or the “main fuse” for an entire fuse panel. 

Cartridge fuses are cylindrical in shape with metal sleeves on both ends. They fit into a fuse block and positioned into a slot in the fuse box. 

For the main fuses, the amperage rating is often 60-amp while cartridge fuses for appliance circuits are rated 30 or 40-amp.

Overloaded Circuit

A circuit overload occurs when too many plug-in appliances are connected to the circuit. These draw excess power that exceeds the capacity of the fuse. The metal strip within the fuses will, therefore, melt, i.e., the fuse will blow.  

This will keep repeatedly happening if the “extra” appliances or whatever is causing the overload are not removed from the circuit. 

To fix this, offload the circuit or move some of the appliances to another circuit, then replace the fuse, and you’re good to go. 

Short Circuit

If there is a loose wire, damaged wire, or damaged wire insulation either in the circuit or within the internal wiring of a device plugged into the circuit, then a short circuit can occur. The electric current strays beyond its intended path due to lack of resistance hence causing excess current flow through the “short.”

Simply replacing the blown fuse, in this case, will not solve the problem. The fuse will keep blowing until you find where the short circuit is and correct it. This will take patience or the help of a professional electrician. But if it is a short within an appliance, then unplugging that device will correct the situation.

Ground Fault

A ground fault is a type of short circuit. In this case, the hot wire in the system touches the grounding wire. The straying current, therefore, flows directly to the ground or touches a grounded part of the system. 

A ground fault will not only blow the fuse but can increase the chances of shock if someone is standing in or is in contact with the path of the fault, e.g., a wet ground.

Correcting a ground fault is similar to the fix for a short circuit. It’s advisable to have an electrician check it out to ensure all is in order.

Wrong Fuse Installed

Installing an “under-rated” fuse in a circuit can result in repeated blown fuse even when the current through the circuit is below the capacity of the circuit wiring. It’s therefore important to make sure you use the correct size of fuse in the circuit. If you have any doubts, have an electrician look at it and advise you.

Conclusion

If your generator keeps blowing a fuse, then the cause is most likely either a current overload in the circuit, a short circuit, or ground fault. If you find none of this, then check if you have the correct size fuse in place because an “under-rated” fuse can keep blowing.

Related Reading:

• Generator Dies Under Load: Likely Cause and How to Fix It
• Generator Starts But Won’t Keep Running? Here’s Why