Learning, Breaker,

Does a Subpanel Need a Main Breaker?

Does a subpanel need a main breaker? As someone who’s worked on a fair share of electrical projects, I understand that this can be a confusing topic, especially for those just starting.

But fear not, my friends, because I’m here to break it down for you(no pun intended). First off, let me answer the question.

Yes, a subpanel should have a main breaker. This is because the main breaker is a crucial safety feature by disconnecting all power to the subpanel if an electrical emergency or fault occurs.

But don’t just take my word for itlet’s explore this topic a bit more. This article will discuss the importance of main breakers in subpanels and some common misconceptions surrounding this topic.

I will also cover some tips on properly installing a sub panel with a main breaker.

Does a Subpanel Need a Main Breaker?

Understanding the Purpose of a Main Breaker

A main breaker is a safety feature that shuts off all power to the subpanel in case of an electrical emergency or fault.

It protects the circuits from overloading and prevents electrical fires. Without a main breaker, the subpanel is at risk of overheating and causing damage to the electrical system.

Code Requirements for Subpanels with Main Breakers

The National Electric Code (NEC) does not require a main breaker in a subpanel. However, it is recommended to install one for safety reasons.

The main breaker must be rated for the maximum current that the subpanel can handle.

If the subpanel is outdoors, the main breaker must be weatherproof and meet the NEC requirements for outdoor installation.

Benefits of Installing a Main Breaker in a Subpanel

Installing a main breaker in a subpanel has several benefits. First, it provides an additional layer of safety to the electrical system.

Second, it lets you shut off power to the subpanel without going to the main panel. This is useful if you need to perform maintenance or repairs on the subpanel.

Third, it can help you save money on your electricity bill by allowing you to turn off power to the subpanel when it is not in use.

Pros and Cons of Subpanels Without Main Breakers

This table outlines some of the pros and cons of subpanels without main breakers to help you decide what type of subpanel is best for your needs.

Pros of Subpanels Without Main BreakersCons of Subpanels Without Main Breakers
Lower cost compared to subpanels with main breakers.Increased risk of electrical shock or fire, especially if proper safety precautions are not taken.
Easier to install since there is no need to connect a main breaker to the main panel.It may not handle the same electrical load level as a sub panel with a main breaker.
It can be more space-efficient since a subpanel without a main breaker can often fit into a smaller space than a subpanel with a main breaker.It may not provide adequate protection for the electrical system in the event of an overload or other issues.
It can be a good option for smaller or simpler electrical systems that do not require the added protection of a main breaker.It may not handle the same electrical load level as a sub-panel with a main breaker.

When it comes to electrical systems, safety is always a top priority. While subpanels without main breakers may offer certain advantages, weighing these against the potential risks and limitations is important.

If you’re unsure about what type of subpanel is best for your particular situation, be sure to consult with a qualified electrician or other expert.

By taking the time to consider your options and seek expert advice carefully, you can ensure that your electrical system is safe and efficient for years to come.

How to Determine the Right Size of Main Breaker for Your Subpanel

It can be frustrating to install a subpanel only to find out that the breaker you installed is too small or too big. I’m here to help you determine your subpanel’s main breaker size.

First, you need to know the amperage of your sub-panel. This is usually written on the label of the subpanel or in the installation manual.

Once you know the amperage of your subpanel, you can determine the right size of the main breaker by following these steps:

  1. Determine the maximum amperage of the subpanel feeder wire. The wire gauge and the length of the wire run usually determine this. You can refer to the National Electric Code (NEC) to determine the maximum amperage of your wire.
  2. Divide the maximum amperage of the subpanel feeder wire by 1.25. This is the maximum amperage that your main breaker can handle. The 1.25 factor prevents the breaker from tripping due to temporary overloads.
  3. Round up the result of step 2 to the next standard breaker size. For example, if the result of step 2 is 48 amps, you should round up to a 50-amp breaker.

It’s important to note that the size of your main breaker should not exceed the rating of your service entrance equipment.

Your electric utility company usually determines this, and it can be found on your electric bill or in the installation manual of your service entrance equipment.

In addition, you should also consider the load that will be connected to your sub-panel.

If you plan to connect heavy loads such as air conditioners or electric heaters, you may need to install a larger main breaker to handle the load.

Common Mistakes to Avoid

I have seen many common mistakes that homeowners make when installing subpanels.

Not Installing a Main Breaker

One of the most common mistakes homeowners make when installing a subpanel is not installing a main breaker.

A main breaker is an essential safety feature that shuts off all power to the sub-panel in an electrical emergency or fault. Without it, the circuits would not be protected from overloading.

Make sure that you install a main breaker in your sub-panel. If you are unsure how to install one, consult a professional electrician.

Using the Wrong Size Wire

Another common mistake homeowners make when installing a subpanel is using the wrong wire size.

The wire size you need depends on the amperage of the subpanel and the distance between the subpanel and the main panel.

Using the wrong wire size can cause the wire to overheat and potentially start a fire. Make sure that you use the correct size of wire for your sub-panel.

Consult a professional electrician if you are not sure what size of wire to use.

Overloading the Subpanel

Another common mistake that homeowners make when installing a subpanel is overloading it.

A subpanel has a limited amperage capacity; if you exceed that capacity, you can overload the subpanel and cause a fire.

Make sure that you do not exceed the amperage capacity of your sub-panel. Consider installing a larger subpanel or upgrading your electrical service if you need more power.

Wrapping Up

A subpanel does not necessarily require a main breaker by code. However, installing a main breaker in a subpanel can provide additional safety and protection in case of electrical emergencies or faults.

As such, it’s important to consult with a licensed electrician and follow all applicable codes and regulations when installing or modifying a sub-panel.

While a main breaker may not be required by code, it can provide peace of mind and added protection for your electrical system.

As always, safety should be the top priority when dealing with electricity, and it is important to take all necessary precautions and follow proper procedures.




  • “Wiring Simplified: Based on the 2020 National Electrical Code (NEC)” by Frederic P. Hartwell and Herbert P. Richter:
  • “Electrical Wiring Residential” by Ray C. Mullin and Phil Simmons:

Video References

Benjamin Sahlstrom

Everyday Home Repairs

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About Alex Robertson

AvatarCertifications: B.M.E.
Education: University Of Denver - Mechanical Engineering
Lives In: Denver Colorado

Hi, I’m Alex! I’m a co-founder, content strategist, and writer and a close friend of our co-owner, Sam Orlovsky. I received my Bachelor of Mechanical Engineering (B.M.E.) degree from Denver, where we studied together. My passion for technical and creative writing has led me to help Sam with this project.

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