What is a Subpanel: Complete Guide to Subpanels

The heart of the electrical system of every home is the main circuit breaker box called the main electrical service panel. It’s the point where power from a utility company enters your home first from the meter. But what are subpanels?

A subpanel is a smaller service panel that enables power distribution to specific areas of your building or home. A subpanel is a satellite circuit breaker panel that extends the capacity of the main panel. A double-pole 240V circuit breaker at the main service panel usually feeds your subpanel with power. The single feed circuit is also divided into several branch circuits at the subpanel.

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It’s from the main panel that power is distributed to several branch circuits in your home. At least every home contains a main service panel. But smaller panels known as subpanels are also as important. Subpanels allow for adding additional circuits for new electrical appliances, additions, or anywhere you need to run new circuits.

According to the National Electric Code (NEC), there’s no limit to the number of subpanels a house can have, provided usage doesn’t exceed incoming capacity.

Here, we’ll focus on what subpanels involve and how you can handle them for effective performance. 

What’s the Difference Between the Main Panel and Subpanel?

The main panel is the power entry point from a utility company into your home. At the same time, a subpanel operates as an intermediary between circuits connected to your property and the main panel. They link to the main panel via a circuit feeder. 

The main panel regulates the power connection and controls the power that gets to the outlet subsidiaries on your property. In most cases, the main panel has circuit breakers to regulate the branch circuits and subpanels. It has a main breaker switch used for disconnecting power entering the panel and all the subpanels that service several areas of your home. 

There is a clear difference between the main panel and the subpanel. However, you’ll find one main circuit breaker as the primary distinguishing difference. 

A subpanel can have different subpanels. Even though a subpanel operates similarly to the main panel, it can’t generate or add more power supply independently. This is because they feed off current from the main panel. 

A subpanel is, therefore, a smaller service panel.

You should install subpanels in your electrical system for several reasons:

  • Separating Usage: Whether operating a restaurant, manufacturing workshop, healthcare facility, dental clinic, mall, school, or shop, you might need various power consumption needs. 

The different areas in your building might have various appliances, equipment, and machinery. If you add a subpanel, you’ll enable the separation of these other areas, thus enhancing the efficiency of your business. 

If you organize the circuit by their related sub-panels, you’ll have an easier time identifying the switches in your building. It’ll also be easier to repair and maintain anything in your circuit. 

For instance, turning off the power supply in one area won’t affect the operation in other areas. 

  • Improving safety: While the main panel is positioned inside your building, a sub-panel can be stationed anywhere. It can be helpful, especially during emergencies or fires when entering your home to switch off the main service panel is dangerous. 

If you turn off your power using the subpanel, you don’t risk any chances of suffering from electrocution. 

  • Adding the circuit space: The main service panel has a maximum number of circuit breakers and switches that it can hold. You should go for a subpanel if you wish to create more room on your circuitry. 

Apart from just having additional space, you’ll also have adequate and safe distribution and regulation of power to the intended areas in your property. 

Is a Subpanel Necessary?

Are you considering adding a new electrical sub panel because your main panel has no more breaker spaces? Wait, you may not need a new subpanel.

If your main breaker box allows for tandem breakers, you can increase your house panel capacity by replacing the existing 1-pole breakers with tandem breakers. Tandem breakers allow for two branch circuits to share one breaker space.

The new circuit breakers can handle the additional branch circuits without needing an electrical panel upgrade or a new subpanel.

Can any Panel be a Subpanel?

You can use a panel as a subpanel but under certain conditions. You can use a standard load center as a subpanel in your building. However, you must remove a neutral bonding jumper in such a case. 

In a subpanel, a neutral is completely isolated from the ground. When you decide to do electrical work, you should completely turn off the power. 

You can only bond the ground and neutral in a single point in the main panel for residential service. You’ll have a machine screw or metal strap connecting the neutral bus bar to most panels’ ground or panel case.

You should therefore remove the screw or metal strap. It’s, therefore, possible to use a panel as a subpanel as long as you make the right connections. 

Are Subpanels Safe?

A subpanel is very safe to operate with. One of the reasons you should use a subpanel is to offer your building and circuit safety.

For instance, if you want to manage any repairs and maintenance in your circuit, you can switch off your subpanel to prevent any power flow. If the power in the subpanel is off, you lessen the risk of being electrocuted.

It would help if you remembered that it’d only take about one minute to shut off the power. However, it takes less than one second to be shocked by the power and get injured. 

Switching off a subpanel before you do repairs or in case of an emergency is one of the safety measures you can ever take to remain safe. It would be best to involve a professional technician in your repairs and maintenance tasks. 

How Does a Subpanel Work?

For a subpanel to work, it needs two hot wires linked to a 240V double pole breaker in your main panel. It also requires a ground wire and neutral wire. 

The cable employed in this run is a three-wire cable with ground. The hot wires are known as feeders and offer power to your subpanel. 

The cables link to the 240V main breaker in your subpanel, connecting power down through the hot bus bars. Each circuit breaker connects to the bus bars to distribute power to branch circuits going through your subpanel. 

It would be best to know that a subpanel doesn’t offer its power into your building but instead relies on the supply from the main panel. 

Does a Subpanel Need the Main Breaker?

Having the main breaker on a subpanel in your building isn’t necessary. However, it isn’t restricted; you can include it if you see fit.

If you want to include a main breaker in your sub-panel, you should remove lugs where the black and red wire was connected and screw or nut the breaker in that exact location. You can then connect the black and red wire to the lugs over the breaker. 

How Many Subpanels Can You Have?

You can install as many subpanels for the main panel of 200 amps as long as the combined demand doesn’t exceed 160 amps.  

Remember that a subpanel is simply a secondary circuit breaker that gets its power from the main panel. 

If you plan to have subpanels in your building, it will help to know the exact number of these devices you need. This way, everything works effectively and doesn’t overload the subpanel. 

It would be best if you did proper planning to keep track of every subpanel you add to avoid exceeding the required amperage. 

How Far Can a Subpanel be From the Main Panel?

You can place a subpanel anywhere in your house regardless of where the main panel is. But, it’s recommended that you mount it at least a foot away from the main panel. There are even instances where a subpanel is placed outside the house while the panel is inside. 

However, the most important thing you should focus on is the installation process and cable selection. You should securely attach your subpanel enclosure to a stable surface or wall with fasteners. 

If you install the subpanel outside, you should go for an approved exterior use enclosure. Depending on the voltage to the ground, you always offer at least 3 to 4 feet of clearance from the panel’s sides.

You should also ensure that the panel is easily accessible. Therefore, it would be best if you didn’t install it far above the floor. The right feet would be between 4.5 to 5 feet. 

The cable from your main panel to the subpanel depends on the amperage rating. For instance, for a 30A panel, use a 10 AWG, three-wire conductor. 

If you have a 60A panel, use a 6 AWG wire. For a 100A panel, a 2 AWG aluminum or 4 AWG copper wire would be appropriate. A three-conductor wire contains four wires inside. 

Where Do You Put a Subpanel?

You can have your subpanel anywhere. It is okay to put it in the interior or the exterior of the house or building. However, the best place to put it is about a foot away from the main service panel. 

Having your subpanel outside your building is a safety measure in an emergency. For instance, if there is a fire, you can easily switch power without moving into your house. 

It would help if you mounted the subpanel on a stable surface or wall to prevent any damage from an external force such as wind. 

Instead of worrying about where to put the subpanel, it’s best to focus on implementing a perfect installation process. 

How to Install a Subpanel

Safety is among the key things you should always focus on while installing a subpanel. Your safety and those should come first to prevent any injuries or even death from electric shock. 

It would be best to switch off the main panel during installation. The installation process is straightforward and takes about 2 hours to complete. 

Tools Required

  • A hammer
  • Screwdriver
  • Flashlight
  • Voltage tester
  • Long-nose pliers
  • Lineman’s pliers
  • Strippers

Materials Required

  • Mounting screws
  • Subpanel
  • Approved feeder cable
  • Approved feeder breaker
  • Staples or cable clamps
  • A breaker for your new circuits

If you lack the skills to do an installation, it would be better to involve a professional expert. Follow the steps below to install a subpanel effectively.

Mount The Subpanel

This is the first step you should implement while installing your subpanel. It would help if you mounted your subpanel almost one foot away from the main panel. 

It would help if you purposely determined how your wires would travel and pulled wires accordingly. You should also add cables and strip the wire sheathing.

This is also the perfect time to remove a knockout slug and slide the wires through. It would be best if you also clamped the cables.

Plan The Route

At your main service panel, plan the route for the wires: neutral wire, ground wire, black hot wire, and red hot wire. 

Start by stripping the sheathing and then removing the knockout slug. You can then clamp the cable. 

Finally, carefully route the ground and neutral wires and link them to the bus bar. 

Strip Wires

Cut, route, and strip the black and red wires. You can then connect them to your feeder breaker. Snap the breaker to its rightful place. 

Connect Wires

The route is cut, and strip the feeder wires in the subpanel. You can then proceed to connect them to the terminals. 

Connect the red and black wires to the hot bus bars. The neutral wire should be linked to the neutral terminal, while the ground wires must be connected to the ground bus bar. 

Run the cable for your new circuits into the subpanel and then clamp those cables. Connect the white wire to the neutral bus bar, the hot wire to your circuit breaker, and route your wires around the perimeter of every circuit. 

Should You Inspect or Replace Your Subpanel?

A proper inspection from a competent professional can make all the difference if you have a subpanel in your building or home. An expert can also recommend whether to replace it or not.

Several issues could come up with the subpanel, including improper bonding, corrosion, and missing handle ties. Another common challenge could be improper wiring. 

Identifying an improper wiring challenge might be more complicated for most business owners or homeowners than you think. If you don’t identify such problems well, they might cause more devastating, more expensive, and more significant issues in the future. 

Always involve a professional inspector or local technician in giving you a clear overview of the issues before escalating further. If your subpanel has any problems, you should replace it immediately. Waiting any longer can translate into danger and injuries to occupants of the building. 

Frequently Asked Questions

What Size Wire for a 125 Amp Subpanel?

A 125 amp breaker panel requires either #2 copper wiring or #1/0 aluminum or copper-clad wiring. For underground service, a minimum 1.25 inch, schedule 40 or 80 PVC electric conduit is required to install a 125 amp electric service or subpanel. 

To wire a capacity of 125 amps, an electric permit and skilled installation by a trained electrician are required.

What Size Wire for a 100 Amp Subpanel?

Wiring a 100 amp breaker panel requires either #4 copper wiring or #2 aluminum or copper-clad wiring. For underground service, a minimum 1.25 inch, schedule 40 or 80 PVC electric conduit is required to install a 100 amp electric service or subpanel.

An electric permit and skilled installation by a qualified electrician are necessary for wiring a garage or room addition with a capacity of 100 amps.

For more, see Wire Size for 100 Amp Electric Service: Complete Guide

What Size Wire for a 60 Amp Subpanel?

Professional electricians recommended the smallest wire size is #6 to #4 AWG. If you’re using aluminum wire, you’ll need a larger size. Because almost all household wires are rated at least 600 volts, amperage is the only thing that matters when determining wire gauge.

The wire size for a 220v, the 60 amp breaker is still between #6 AWG and #4 AWG. On the other hand, some electricians advise using only #4 AWG wires when installing 60 amp breakers.

A #4 AWG wire holds more amperage than the 6 AWG. For example, a 4 AWG copper wire can comfortably have 70 Amps of power before overheating to the point you trip circuit breakers. On the other hand, a #6 AWG can have about 55-Amp before overheating to the point you risk tripping the circuit breaker.

For more, see How To Wire a 60-Amp Breaker: (Explained with Video Guide)

Can a 200 Amp Panel be a Subpanel?

You can use a 200 amp panel as a subpanel. When the main disconnect is outside by the meter, the inside 200 amp panel is already wired as a subpanel. Subpanels are not bonded and have a 4-wire setup where two hot wires, a neutral wire connected to the neutral bar, and a ground wire connected to the ground bar inside the electrical box.

We see cases routinely where a house will have two 200 amp breaker panels. What’s most important is that you don’t exceed the capacity of the incoming service. Increasing from a CL200 meter to a CL320 meter may be necessary, depending on your needs.

For more, see How Many Subpanels Can You Have On 200amp Service?

Conclusion

A subpanel is a smaller panel that allows power distribution to specific areas of your building or home. It’s supplied with a double pole 240V from the main electrical panel. 

You should take safety precautions into account while mounting your subpanel. For instance, it would be better to mount it on a stable surface. You should also ensure that the main panel power is switched off.

It would also help to do regular inspections on your subpanel to identify any challenges. If there are any problems with your panel, you should immediately fix them. However, if you don’t have the required skills, it would be best to involve a professional electrician. 

Do You Need an Electrician?

Get FREE quotes from licensed electricians in your area today. Whether you need an outlet or ceiling fan installed or a new electrical panel or wiring, We Can Help! All electricians are screened, licensed, and insured.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.
DISCLAIMER: The content published on HomeInspectionInsider.com is not professional advice. You should consult with a licensed professional and check local permit requirements before starting any project.
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