What are Subpanels: A Complete Guide to Subpanels

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

Here’s what I know from being a Master Inspector for decades:

A subpanel is a smaller panel that enables the distribution of power to specific areas of your building or home. It’s simply a satellite circuit breaker having its breakers. Your subpanel is usually fed with power by a double-pole 240V circuit breaker at the main service panel. The single feed circuit is also divided into several branch circuits at the subpanel.

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 subpanels are also as important.

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

What Is The Difference Between The Main Service Panel And
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Why Home Inspections Are Important
A Subpanel?

The main panel is the entry point of power 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 amount of power that gets to the outlet subsidiaries in your property. The main panel has about 6 circuit breakers to regulate the branch circuits and subpanels in most cases. It has a switch used for disconnecting and 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 pullout fused disconnector and the main circuit breaker most of the time. 

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 you are 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 different types of appliances, equipment, and machinery. If you add a subpanel, you’ll enable the separation of these different 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. If you wish to create more room on your circuitry, then you should go for a subpanel. 

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

Can I Use Any Panel As 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, in such a case, you must remove a neutral bonding jumper. 

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 the ground or panel case in most panels.

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 safety to your building and circuit.

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 you about one minute to shut off the power. However, it takes less than one second to be shocked by the power and get injured in the process. 

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 if you involved a professional technician in your repairs and maintenance tasks. 

How Does A Subpanel Work?

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

The cable employed in this run is referred to as a three-wire cable with ground. The hot wires are known as feeders, and they 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 if you know that a subpanel doesn’t offer its power into your building but rather relies on the supply from the main panel. 

Does The Sub Panel Need The Main Breaker?

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

Never forget 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 of 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 ensure that you securely attach your sub panel 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 clearance from the panel’s sides.

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

The cable running 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 case of 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 damages 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 if you switched off the main panel during the installation process. 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 right 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 the extent that your wires will travel and pull 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 remove the knockout slug. You can then clamp the cable. 

Finally, route the ground and neutral wires carefully 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, 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 for every circuit. 

Should You Inspect Or Replace Your Subpanel?

If you have a subpanel in your building or home, a proper inspection from a competent professional can make all the difference. 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. 

For most business owners or homeowners, identifying an improper wiring challenge might be more complicated 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 they escalate 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. 

Conclusion

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

References:

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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.

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