A subpanel, also known as a load center, is an essential component of a home’s electrical system. It works in conjunction with the main service panel to distribute power throughout the home. For homeowners, understanding what a subpanel is and how it functions can help ensure your home’s electrical system remains safe and reliable. This comprehensive guide will explain everything you need to know about subpanels for your home.

What is a Subpanel?

A subpanel is a secondary electrical panel that derives power from the main service panel. The main service panel is the central hub of your home’s electrical system, receiving power from the utility company and feeding electricity through large-gauge wires to subpanels located throughout the house. Subpanels then distribute power to individual circuits that serve lights, outlets, and appliances in specific areas of the home.

In a way, you can think of the main panel as the “heart” of your electrical system and subpanels as smaller ” hearts” helping circulate electricity throughout your home. Subpanels expand the number of available circuits in your home and allow localized control over those circuits. Without subpanels, homes would require exceptionally large main panels and extensive wiring running back to a single location.

Why are Subpanels Used in Homes?

There are several important reasons subpanels are commonly installed in homes:

Expand Circuits: The main breaker panel usually doesn’t have enough space for all the circuits a modern home needs. Subpanels increase the number of available circuits.
Control Circuits Locally: Subpanels allow you to group and control circuits by location, such as by floor or by room, for convenience.
Reduce Wire Runs: Locating subpanels around the home shortens the distance power needs to run through wiring. This uses less copper and can improve efficiency.
Manage Load: Distributing electrical load across subpanels balances draw and reduces strain on the main panel and service entry wires.
Meet Code Requirements: Electric code requires a certain number of circuits for lighting, outlets, specific rooms, and appliances. Subpanels help ensure these requirements are met.
Safety: In case of an overloaded circuit or short, a subpanel breaker will trip before the main, reducing risk and isolating the issue.
Add Circuits in the Future: Subpanels make expanding circuits easier for additions, renovations, and new wire-intensive appliances.

Without subpanels, even a modest home would require an exceedingly large and complex main service panel. Subpanels allow homes to have an intelligently designed electrical system that provides capacity, control, and safety.

How Does a Subpanel Get Power?

Subpanels are always fed power from the main service panel. Thick wires, usually gauge #3 or #2 AWG copper, run from the main breaker through conduit over to the subpanel. The subpanel does not have its own separate power supply or meter from the utility company like the main panel does. The number of subpanels in a home depends on the size of the home and number of circuits required.

Inside the subpanel, the hot wires coming from the main panel connect to a “feed breaker” that serves as the master cutoff switch for that subpanel. This feed breaker is sized according to the subpanel’s capacity and is often between 60 amps to 100 amps. If an issue ever occurs in that subpanel, its feed breaker could be switched off without affecting other subpanels or the main service panel.

Ground and neutral wires also run between the main and subpanel. The neutral provides a safe return path for the current while the ground protects from shocks and shorts. Without a properly fed subpanel connected back to the main service panel, a subpanel would have no power source of its own to distribute electricity.

120V vs 240V Circuits in Subpanels

Like the main service panel, subpanels provide both standard 120-volt and higher 240-volt circuits to your home.

120V circuits serve regular lights, outlets, and small household appliances. They consist of a hot, neutral, and ground. The 120V is the potential difference between the hot and the neutral. These circuits supply smaller loads around the home that don’t require as much power.

240V circuits serve larger appliances like electric dryers, stoves, ovens, air conditioners, and hot water heaters that require more electrical power. They have two hot wires that each carry 120V relative to the neutral to create 240V between the two hot wires. No neutral is required. The ground is still included for safety.

A subpanel will have a mix of both 120V and 240V circuits fed by the panel’s supply voltage coming from the main service panel. The 120V circuits will take up more spaces in the subpanel since they require a hot and a neutral compared to just two hots for 240V.

Subpanel vs Main Panel: Key Differences

While subpanels and main panels both distribute electricity throughout your home, there are some important differences:

Power Supply: The main panel gets power directly from the utility line while subpanels are fed from the main panel.
Location: Usually only one main panel located near the utility service entry point; subpanels wherever they’re needed.
Metering: Main panel contains the kWh meter and is the demarcation point to the utility. Subpanels have no metering.
Breakers: Main panel has the large main breaker that shuts off all power. Subpanels don’t.
Size: Main panels are very large to manage the total home load. Subpanels come in smaller sizes.
Circuits: The main panel often houses the service entrance wires, larger appliances, HVAC. Subpanels have branch circuits.

While their functions overlap, the main and subpanels each serve distinct roles in a complete electrical system.

Key Components of a Subpanel

Subpanels contain most of the same major components as a main service panel, just on a smaller scale tailored to supply a specific section of the home. Key components include:

Enclosure – Contains and protects all the inner components. Made of thick metal.
Bus Bars – Thick strips of copper that carry the incoming and outgoing power.
Breakers – Overcurrent protection devices that trip to prevent overloads. Control circuits.
Lugs & Terminals – Secure points to connect external and internal wires to the panel.
Neutral & Ground Bars – Where neutral and ground wires are consolidated and attached.
Dead Front – The removable metal plate covering the wires and terminals for safety.

High capacity subpanels also include features like main breakers, ground fault circuit interrupters (GFCIs), and surge protective devices (SPDs) for maximum safety and protection, similar to a main service panel.

Subpanel Breaker Box Sizes

Subpanels are available in a range of standard sizes depending on the number of circuit spaces needed:

12 circuit – Smallest, often used for simple additions like a bathroom or small kitchen.
16 circuit – For a kitchen, workshop, or isolated area with multiple circuits.
24 circuit – Typical for adding a bedroom, office, or finishing a basement or garage.
30-42 circuit – Used for additions, kitchen/laundry renovations, shops.
60 circuit and up – Larger projects like add-on wings and room build-outs.

Like the main panel, the number of circuit spaces needed depends on your home’s electrical demands and code requirements. It’s better to install a subpanel with room to grow than max out its capacity right away.

The two main subpanel box sizes are “flush mount” for new construction and “surface mount” for retrofits:

Flush Mount – Recessed inside the wall like a main breaker panel. More aesthetic.
Surface Mount – Mounted externally to the wall surface. Useful for retrofits and additions.

There are also special “load centers” designed for easy installation in garages, basements, or standalone structures.

Subpanel Installation Codes

Subpanels are a major component of a home’s electrical system and must be installed properly to NEC (National Electrical Code) standards and local codes. Key requirements include:

Circuit Directory – Labels each circuit and its purpose. Often inside the panel door.
Clearances – 30 inches minimum in front. 6 feet access space in front.
Location – Readily accessible. Not in bathrooms or above stairways.
Height – 6 feet 7 inches maximum to top of panel.
Feeder Wires – Proper size copper conductors in conduit. Required disconnect means.
Overcurrent Protection – Feeder breaker sized for wire gauge and capacity.
Bonding – Properly bonded neutral and ground bars. No shared neutrals.
GFCI Protection – For circuits serving wet areas, outdoors, garages and basements.
AFCI Protection – For most lighting and outlet circuits. Prevents electrical arcs.

Consult a qualified electrician to ensure proper code compliance and safety when installing a subpanel. Don’t take chances with electrical work.

Upgrading an Old Fuse Box to a New Subpanel

Many older homes still have outdated fuse boxes instead of modern circuit breaker panels. Upgrading to a new subpanel is highly recommended for safety, capacity, and electrical system management.

The process for replacing a fuse box with a new circuit breaker subpanel includes:

Turn off power at the main breaker panel. Verify it’s off!
Remove the old fuse box.
Install new subpanel as desired – flush or surface mount.
Run conduit and THHN wires from main panel to subpanel.
Connect neutral, ground, and hot wires securely.
Label all the circuits in the new subpanel directory.
Connect existing branch circuit wires to new breakers.
Attach cover plates and dead front.
Turn power back on and test circuits.

Replacing an antiquated fuse box provides many benefits:

Added Circuits – More capacity for new lighting, outlets, and appliances.
Safety – Breakers prevent overloads better than fuses. AFCI and GFCI protection. Better grounding.
Convenience – Individual breakers for each circuit are much easier to reset than fuses. Easier to de-energize individual circuits for work.
Reliability – Breakers won’t blow from temperature changes like fuses can. Fewer neutral connection issues.
Resale Value – Modern electrical service appeals to buyers and meets code requirements.

While costs can range from $1,500 to $3,000 or more, upgrading old fuse panels to circuit breaker subpanels provides tremendous value and peace of mind.

Common Subpanel Issues

Subpanels are generally quite durable and reliable. However, issues can occur over time:

Overheating – Check for overloads. Clean out dust. Ensure proper wire sizes.
Corrosion – Loose and corroded connections cause heating and resistance. Resecure and clean connections.
Shorted Breakers – If a breaker trips repeatedly, a short may be present in the wiring or at an outlet or junction. Inspect connections and wiring.
No Power – Check the subpanel’s feed breaker at the main panel. Verify main breaker is on. Check for any tripped GFCI outlets.
Burning Smell – Discontinue use immediately. This indicates overheating electrical components and wiring. Have an electrician inspect and repair.
Buzzing/Crackling – Arcing sounds from a subpanel often indicate a serious issue like loose hot bus connections. Power down and call an electrician promptly.

Warning: If a subpanel exhibits signs of failure like burning smells or crackling noises, shut it off at the main panel immediately and call an electrician before using any of the circuits fed by that subpanel again. Electrical issues can lead to fires and present serious health hazards if not addressed.

Subpanel Safety Tips

Practicing proper electrical safety is extremely important when working with subpanels. Key tips include:

Always turn off the main breaker when accessing electrical components inside a subpanel. Verify it’s off!
Use a non-contact voltage tester on wires before touching to double check they are de-energized.
Only use properly rated insulated tools when working inside an energized panel. Never use everyday household tools.
Wear electrical safety gloves, glasses, and avoid conductive jewelry when servicing a panel.
Ensure circuits are properly labeled. Identifying live wires prevents mishaps.
One hand in the pocket rule – don’t provide a path for current across your chest when using one hand in a live panel.
Avoid water and damp environments when working on panels.
Never overtorque connections or damage can occur. Tighten to spec.
Use caution when reaching inside as bus bars remain live. Don’t contact them.
Replace missing panel covers immediately before an accident occurs.
Service panels only if you are fully qualified and trained to do so safely.

Subpanels contain hazardous high voltage. Contact a professional electrician for anything beyond very minor subpanel work. Safety should be the top priority when maintaining and improving your electrical system.

Common Subpanel Questions

Q: How many subpanels can you have in a home?

A: There is no specific limit. It’s common to have 2-6 subpanels depending on the home’s size and number of circuits required. The electrical load and wire sizing will dictate how many subpanels can be safely added.

Q: Can you add circuits to a subpanel?

A: Yes, if the subpanel has available spaces new circuits can be added by connecting new breakers. If at capacity, a larger subpanel may need to be installed.

Q: Do subpanels need their own ground?

A: No. Subpanels use the same ground system as the main panel they are fed from. The ground wire is extended from the main panel to the subpanel.

Q: How do you wire a subpanel?

A: Run thick feeder wires in conduit from the main panel to the subpanel. Connect the hot wire(s) to the feed breaker, neutral to the neutral bar, and ground to the ground bar. Follow codes for wire sizing.

Q: What size breaker is needed for a subpanel?

A: The feed breaker for a subpanel should be sized slightly larger than the total amperage of all circuits in the subpanel. For example, 100 amps for an 84 amp subpanel load.

Q: Do I need a permit to install a subpanel?

A: Most likely yes. Electrical work like installing subpanels typically requires permits and inspections to meet local electrical codes. An electrician can ensure proper permitting.

Q: Can you install a subpanel in an outbuilding?

A: Yes, subpanels are commonly installed in detached garages, workshops, barns, and sheds to supply power from the main house panel. Specific codes apply for feeder wires.

Conclusion

Understanding subpanels is important for homeowners seeking to maintain and improve their electrical systems. Subpanels allow homes to have the capacity, flexibility, and redundancy needed for today’s modern electrical demands and code requirements. Installing them properly by trained electricians ensures safety and functionality. While subpanels share similarities with main panels, they serve distinct roles in power distribution. With the information in this guide, homeowners can better recognize when and why their home may need additional subpanels as well as how to identify any issues needing correction by a qualified professional. Knowledge of your home’s electrical system leads to making informed decisions when upgrades are called for.

Subpanels Explained for Home Owners