What is an Electrical Sub-Panel?

An electrical sub-panel is simply a secondary electrical distribution panel inside the home or on the property. Sub-panels generally receive electricity from a home’s main electrical service panel, and send power out along feeder and branch circuits throughout the home. The fundamental difference between electrical main panels and sub-panels are the source of electricity. Main panels receive power directly from the utility provider, whereas a sub-panel receives power from the main electrical panel via a circuit breaker. The other critical differentiator is how grounding is handled in each panel. One requires a main bonding jumper installed while the other does not, additionally, installation of a sub-panel in remote buildings requires supplemental grounding electrodes, more on that in a later article. Sub-panels come in various sizes, the most common are 30, 60, and 100-ampere panelboards. There are numerous applications for an electrical sub-panel which we will explore in this article. 

Do I need to Install an Electrical Sub-Panel?

There are three primary reasons for choosing to install an electrical sub-panel. The first and most common are space constraints. In this scenario, the main electrical circuit breaker panel does not have enough available spaces to add a new branch circuit. Alternatively, where added protection is code required or homeowner elected, the existing electrical main panel may not have room inside the cabinet or on the bus bar for a GFCI (Ground-Fault Circuit Interrupter) or AFCI (Arc-Fault Circuit Interrupter) circuit breaker. For example, a standard 100-amp electrical main panel may have a bus bar with 24 total slots to plug circuit breakers. If all 24 positions are filled with single and double pole circuit breakers, then in the event a new branch circuit is needed, the existing main panel could not accommodate. That being said, ultra-thin circuit breakers are available. Those breakers are known as tandem, duplex, or peanut breakers. Tandem circuit breakers provide two single pole 120-volt circuits in a single plastic body capable of fitting into the space of one standard circuit breaker. Tandem circuit breakers are identified by two breaker mechanisms side by side on the front face of the breaker. There are some challenges when using duplex circuit breakers. Not all AHJs (Authority Having Jurisdiction) will approve the use of tandem circuit breakers. When the AHJ does allow the use of duplex circuit breakers, there will likely be a maximum limit that can be safely installed. This is because two circuits inside a single plastic circuit breaker body will have a hard time safely dissipating heat generated. Additionally, tandem circuit breakers are not available with either GFCI or AFCI protection, further limiting their use given current NEC (National Electric Code) requirements. Given the limitations and challenges associated with tandem circuit breakers, the overall best solution for a lack of space in the main electrical circuit breaker panel is to install a sub-panel. Given societal changes toward renewable energy and government incentives encouraging electrification, sub-panels will no doubt play a critical role in residential PV (Photovoltaic) solar systems, and EV charging infrastructure.  

Wiring Efficiency on New Construction or Addition

The second reason for installing an electrical sub-panel involves wiring efficiency, particularly on new home construction or home additions. When the electrical service panel is located on one side of a home versus near the center, individual electrical home run branch circuits may become very long, which is particularly problematic in larger homes. Longer electrical wires have inherently more resistance to current flow, and therefore generate far more heat. Additionally, long electrical circuits can experience power quality issues such as excessive voltage drop. Higher quantities of heat can degrade wire insulation and increase the probability of home fires while large voltage drops create excessive wear and tear on appliances, particularly those equipped with electric motors or sensitive electronics. Additionally, longer electrical circuits require significantly more copper wire and are much more expensive to install. Installing an electrical sub-panel in a location effectively shortens multiple home run circuits while achieving significant efficiencies. This is accomplished by installing one large feeder circuit from the electrical main panel to supply electricity to the sub-panel. Consequently, each individual electrical branch circuit from the sub-panel becomes shortened. This is accomplished by terminating the branch circuits at the much closer sub-panel versus installing longer wires back to the distant electrical service panel. An electrical sub-panel installation generally is a cost-effective option, producing less heat and creating less voltage drop.

Homeowner Convenience

Finally, the third primary reason for installing an electrical sub-panel is convenience. If, like most homes, the electrical main panel is located in a basement or far distant part of home, the homeowner must traverse one or more flights of stairs and potentially cross the length of the home, and potentially move personal property to reach the main electrical panel. This is especially problematic in larger homes with two or more stories, a basement, and homes exceeding 4000 square feet. Adding an electrical sub-panel to each floor or section of a home can be thought of as electrical zoning, providing a great deal of convenience. In the event of a tripped circuit breaker, reaching the electrical panel is significantly closer and much easier to reach. Additionally, the installation of an electrical sub-panel allows for electrical expansion by providing additional unused circuit breaker slots for future circuits. Today, common circuit additions in a residential home include, EV charging stations, and PV solar arrays. Lastly, sub-panels are very convenient for remote locations on a single property. For example, if the home has a detached garage or outbuilding in which the homeowner chooses to equip with electricity, an electrical sub-panel is the most efficient, convenient, and cost-effective approach.

Performance Group Electrical Sub-Panel Installation in Kansas City

An electrical sub-panel can be a practical component of a home’s electrical system. When chosen, a quality electrical sub-panel installation should be both, code compliant, and electrically sound delivering an efficient, convenient and cost-effective solution. Consider hiring a licensed electrical professional with expert knowledge to protect your family and your home. An investment in a safe electrical sub-panel can save tens of thousands in fire restoration, and most importantly save lives.

At Home Performance Group, we continue to invest in electrical technical training so we can safely install electrical sub-panels. We have performed numerous service upgrades, main panel replacements, and sub-panel installations for our clients.

If you are interested in a no-cost in-home consultation, schedule with a Solutions Advisor today. 

Article by Larry L. Motley Jr., 18 October 2021

Larry is a graduate of both Wentworth Military Academy and Missouri Western State University earning a double bachelor’s degree in Economics and Finance. Additionally, he maintains six professional tradesman licenses in two states and advanced credentialing in green technology, project and program management, and process improvement. Larry is a three-time combat veteran having served in Operation Iraqi Freedom, Operation New Dawn, and Operation Inherent Resolve. He continues to serve through a value-based building science company focused on providing clients the best design, highest quality installation, and most honest repair services in the community.