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HomeTips & GuidesAuto Circuit breakers: When and How to use them on your auto wiring harness

Auto Circuit breakers: When and How to use them on your auto wiring harness

About Auto Circuit Breakers, Many new and modern electronic vehicle accessories are coming up to enhance your driving experience.

You can do it independently if you also want to modify or upgrade your vehicle accessories. However, you need to follow a proper safety system so that new and old accessories are not damaged.

Several components are installed in a vehicle to protect these accessories: fuse, circuit breakers, fuse blocks, etc. However, putting the suitable components with the correct specifications in the right place is essential.

In the following article, we will read about auto circuit breakers and their importance for the safety of your car’s electronic accessories.

Table of Contents

Automotive fuse and its types:

An auto fuse is a piece of metal that connects two wires and cables in the automobile’s electronic system. It’s an intentionally weak connection that melts and breaks whenever a high current flows through the circuit.

With its melting, the connection breaks, and the high current fails to damage electronic parts. Once the fuse melts or breaks, you must replace it with a new one and restore the connection. 

In a car’s electronic system, there are different types of automotive fuses: 

ANL and MANL (mini ANL):

The current rating of these fuses is up to 300 amps; thus, you can find it in high-current applications.

Blade fuse:

Modern automobiles have this type of fuse. These fuses have four main categories: Micro, Mini, Standard, and Max. The current rating for this fuse is up to 100 amps. 

Glass tube fuse:

You can find this fuse in old cars. AG or automotive glass as a suffix in these fuses’ designation. The current rating for this fuse is up to 30 amps.

Fuse holder/Fuse block:

As the name clears, a fuse holder holds the fuse safely and protects the cable that a fuse connects. A fuse holder ensures that the fuse and its connection remain protected. 

On the contrary, a fuse block has different fuse circuits that distribute current to different electronic systems of a vehicle.

In the multiple fuse circuits of a fuse block, a current overload in one circuit will not affect other circuits. You can find your vehicle’s fuse block in the interior fuse box.

Fuse blocks comprise insulating thermoplastic and flame-resistant material to prevent fires in case of current overloading.

Fuses, relays and fuse blocks in the interior fuse box

Fuses, relays and fuse blocks in the interior fuse box

Auto circuit breakers and their types:

Circuit breakers are similar to fuse as they also protect the circuits when there is an overflow of current.

However, the main difference between fuses and circuit breakers is that they do not melt or break on interruption with current overflow but reset themselves to prevent damage.

When the auto circuit breaker works, there is no need to buy and replace any part, as everything is intact inside the circuit breaker case. However, you may need to replace it when there is damage or it stops functioning.

Automotive and marine applications need high ampere circuits.  To ensure the safety of vehicle electronics, you need the auto-reset breaker,12-volt breaker or shortstop. 

This circuit breaker is best for adding any accessory, like a light or 12-volt device. There are different types of auto circuit breakers available:

Type I or automatic reset:

As the name suggests, these circuit breakers reset themselves automatically once opened.

If the overcurrent condition prevails for a long time, the ON and OFF cycle will continue until the overcurrent condition becomes normal.

Due to this cycling of ON/OFF position, you can also call them cycling breakers. 

These breakers do not correct the fault condition but only react by cycling. Thus, if you notice a type I circuit breaker operating ON and OFF, you must rectify the problem immediately.

After all, it’s not good for vehicle electronics to work under faulty current conditions for a long time. 

Type II or modified reset:

When a high current (higher than the breaker capacity) flows through these circuit breakers, they will trip. They will remain in this position until the circuit has power.

You can reset them by turning them OFF or the IGNITION OFF. You may also know these breakers as non-cycling breakers as they do not cycle between ON and OFF conditions.

Type III or manual reset:

You must manually reset the lever once the circuit breaker trips off in these circuit breakers. Some of these breakers also come with a switch allowing you to use the button to de-energize the circuit.

Auto circuit breaker

Auto circuit breaker

Once Fuse, Now Auto circuit breaker:

Which one should you pick when the fuse and circuit breaker function similarly? Mostly, it’s good to use a fuse, but if you use a circuit breaker instead, enjoy the following benefits.

Operation principle:

As you read above, the fuse is a physical connection that breaks or melts on current overflow, while the circuit breaker is a mechanical connection that disconnects on current overflow.

A circuit breaker only needs a reset, while a fuse needs replacement when it breaks. Due to this reason, people prefer circuit breakers more than fuses.

It’s good to use a fuse only if you have spare fuses. On the other hand, you need not carry spares with circuit breakers as they only require flicking a switch.

Switching action:

You can use a circuit breaker in ON/OFF switches but not a fuse.

Wide application:

Fuses are best for circuits rated for 30-50 amps of current, while circuit breakers are suitable for up to 200 amperes for high-current circuit systems.

You can use circuit breakers in accessory and auxiliary circuits of buses, RVs, trucks, and boats. You can also use them in battery charging systems.

Auto fuse box protecting your wiring harness

Auto fuse box protecting your wiring harness

Step-by-step instructions for installing a 12-volt circuit breaker:

Prepare what you need:

Wire for your breaker: 

For a 12-volt device, you will typically need a wire size ranging from 16-4 gauge and 15-20 feet long. You can use a circuit breaker ranging from 5-60 amps for this wire size.

Shortstop breaker of correct amperes according to the load (for instance- amplifier):

Out of the two circuit breaker terminals, one is labeled for battery and the other as an output to the new load. Thus, the current flowing in one direction or the other creates the same heat.

So, it doesn’t matter how you wire a breaker, but following the manufacturer’s instructions is always good.

If you put too many devices receiving power from the system simultaneously, it will trip. For instance, you have an amplifier and subwoofer in the car, simultaneously taking power from the same system.

In such a situation, there are chances that the circuit will trip.

So, while using a circuit breaker, you must be vigilant of the devices drawing power from the car’ system at one time so that you do not overload it.

Accessories for installation

Terminal connectors and crimpers

Wire cutter and stripper

Battery or power source

Step 1: Preparing the wires

Making two-way connections (positive and ground) in automotive wiring applications would be best. 

Before measuring the wire length, putting the accessory in your car’s desired location is good. Also, put a breaker’s mounting bracket in the proper position.

While you mount the breaker, put the terminal face towards the battery to establish a positive connection.

Now, measure the wire length. Start from the load to the ground supply and another wire to the breaker. Next, measure the wire length from the circuit breaker to the battery.

The measurement should be taken carefully so that the wire length is enough from accessory to breaker and according to the wire laying arrangement in your vehicle.

Step 2: Connecting the wires:

Firstly, put terminal connectors at the ends of each wire. Use a wire stripper and cutter for this. For circuit breaker wire, it is advisable to use ring connectors for a secure and tight setup. 

It’s time to make the connection once you connect all the terminal connectors. Connect the accessory’s ground terminal to the ground supply.

Connect the breaker to the battery and the load through a positive connection.

Step 3: Testing your work

Once you connect all the wires, you have finished the circuit installation for your accessory. Now, check if the connections are working fine. Switch on your accessory and see if it works correctly.

It is easy to install simple accessories, but accessories with multiple wirings or 12-volt breaker panels for RV electric systems are sometimes difficult.

You may need help with a wiring diagram. Calling a professional if you fail to understand the diagram properly is good.

Custom wiring harness for your plug-and-play installation

Custom wiring harness for your plug-and-play installation

Why are fuses preferred over circuit breakers for low-current applications?

Several reasons will make you pick fuses over circuit breakers for low-current circuits. 


Fuses are undoubtedly cheaper than breakers. Buying a 12-volt fuse will cost you a few cents and a holder a few dollars. On the other hand, a circuit breaker of a similar capacity will cost around $20-$100.

Response time:

In the conditions of current overflow, a fuse responds in 0.02 seconds, while a circuit breaker responds in between 0.02 and 0.05 seconds.

Voltage drops:

The circuit breaker has a dome-shaped button, and all the current passes through this tiny contact area. As a result, there is expected to be more voltage drop in circuit breakers than in fuses.


In auto circuit breakers, a huge electrical arc is created when the contacts open during high current conditions.

The breaker seems to not get damaged with this arc, but the arcing damages the contact area quality and increases the resistance.


There are chances that the circuit breaker welds itself when a high current passes through it before the contacts open up with the heating up of the bimetallic spring.

If the terminals of the breaker weld together, it may fail to protect the battery or the alternator from a short circuit.


It protects your vehicle’s electrical circuit from current damage, whether a fuse or a circuit breaker. They have the same purpose and usage depending on the electric load capacity.

If you need clarification about using wiring harnesses and cable assemblies with fuses and breakers in your car’s electrical system, contact Cloom. We will guide you thoroughly for smooth functioning.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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