Many homeowners and DIY enthusiasts reach a point where their existing electrical service panel can no longer accommodate new circuits. Whether you’re adding a workshop, expanding your kitchen with high-power appliances, or installing an electric vehicle charger, the solution often lies in learning how to install sub panel. This crucial upgrade provides additional circuit breaker slots, distributing power safely and efficiently from your main panel to a specific area of your home. While the task requires careful planning and a solid understanding of electrical systems, it is a manageable project for those with advanced DIY skills. This guide will walk you through the entire process, from planning and permits to the final connections, ensuring you can install sub panel correctly and safely.
Before you even pick up a tool, the first step to install sub panel is thorough planning. This involves assessing your electrical needs, choosing the right location, and selecting the appropriate equipment. You must determine the amperage rating required for your new sub panel. Common sizes for residential applications are 60-amp, 100-amp, or even 125-amp panels. The total load of all the circuits you plan to run from the sub panel will dictate this size. The location is equally critical. It should be easily accessible, in a dry location, and as close as practical to the main panel to minimize the length of the feeder cable, which can be costly. The National Electrical Code (NEC) specifies clear working space requirements: at least 30 inches wide, 36 inches deep, and 78 inches high in front of the panel must be kept clear. Once you have a plan, you must check with your local building department. A permit is almost always required to install sub panel, and the work will need to be inspected to ensure it meets code, a non-negotiable step for safety and insurance purposes.
Gathering the correct materials is the next crucial phase. Trying to install sub panel with incomplete or incorrect parts will lead to frustration and potential hazards. Here is a comprehensive list of what you will typically need:
- Sub Panel: Choose a panel with enough spaces for your immediate needs and a few extra for future expansion. Ensure it is rated for the amperage you require.
- Feeder Cable: This is the heavy-gauge cable that will carry power from the main panel. For a 100-amp sub panel, you will likely need #3 AWG copper or #1 AWG aluminum THHN wire in a conduit, or a 2-2-2-4 Aluminum SER cable for certain applications. The exact size depends on the amperage and the distance.
- Circuit Breaker: You need a double-pole breaker of the correct amperage for your main panel that will serve as the disconnect for the sub panel.
- Conduit and Fittings: If required by code for your installation method, you will need rigid or EMT conduit, elbows, and connectors to protect the feeder wires.
- Grounding Bar: Most sub panels come with a neutral bar that is bonded to the panel. You must remove this bond and often need to purchase a separate grounding bar since the neutral and ground must be isolated in a sub panel.
- Grounding Rods and Wire: You will need to establish a ground at the sub panel location with one or two grounding rods and the appropriate grounding wire.
- Various Hardware: Wire nuts, screws, cable clamps, and weatherproof seals (for outdoor installations) are essential.
Safety is the absolute highest priority when you work to install sub panel. Electricity is unforgiving. Before starting any work inside your main service panel, you must shut off the main power breaker. However, be aware that the wires feeding the main lugs are still live unless the utility company disconnects your service. This is an extremely dangerous area. Use a voltage tester on the main lugs (with the main breaker off) to confirm they are live, reinforcing the danger. Always treat every wire as if it is live. Wear safety glasses and use insulated tools. If you are uncomfortable at any point, especially working in the main panel, stop and hire a licensed electrician. The cost of a professional is far less than the cost of a serious injury.
With the power off and safety gear on, you can begin the physical installation. Start by mounting the sub panel enclosure securely to the wall using heavy-duty screws anchored into studs. Next, plan the route for the feeder cable from the main panel to the sub panel. If you are running conduit, install it first. Then, carefully measure and pull the feeder wires through the conduit. A key point when you install sub panel is understanding the separation of neutral and ground. In the main service panel, the neutral and ground bars are bonded (connected). In a sub panel, they must be kept separate. This is a critical code requirement for safety. Install a separate grounding bar in the sub panel if one is not already present. The feeder cable will have four wires: two hot wires (usually black and red), one neutral wire (white), and one ground wire (bare copper or green).
Now, make the connections at the sub panel first. Connect the two hot wires to the main lugs of the sub panel. Connect the white neutral wire to the neutral bar. Connect the bare ground wire to the new grounding bar you installed. Ensure all connections are tight. Next, at the main panel, install the new double-pole breaker. Connect the two hot wires from the feeder cable to this new breaker. Connect the white neutral wire to the main panel’s neutral bar. Connect the bare ground wire to the main panel’s grounding bar. Before closing any panels, double-check every connection against a reliable wiring diagram. A mistake here can cause a short circuit or create a serious shock hazard.
The final and most critical step to properly install sub panel is establishing a grounding system. At the sub panel location, you must drive one or two eight-foot grounding rods into the earth, at least six feet apart. Connect these rods to the sub panel’s grounding bar with a continuous, unspliced grounding wire (typically #6 AWG copper for a 100-amp panel). This grounding electrode system provides a path for fault current to dissipate into the earth, a fundamental safety measure. Once everything is connected and before energizing the system, call for your inspection. The inspector will verify that the work is up to code. Only after passing inspection should you proceed.
With the inspection passed, you are ready for the moment of truth. Ensure all the breakers in the new sub panel are in the OFF position. Then, go to the main panel and turn on the new double-pole breaker that feeds the sub panel. Finally, go back to the sub panel. You should see a voltage indicator light (if equipped) turn on. Use a multimeter to check the voltage between the two hot lugs; you should read 240 volts. Between each hot lug and the neutral bar, you should read 120 volts. If all readings are correct, you have successfully completed the core task to install sub panel. You can now turn on the individual branch circuit breakers as you connect loads to them.
Successfully learning to install sub panel is a rewarding project that significantly upgrades your home’s electrical infrastructure. It provides the flexibility to power new additions, workshops, and modern appliances safely. However, it is not a project to be taken lightly. The risks associated with working on a home’s electrical system are substantial. If any part of this process seems beyond your skill level, especially the work inside the main service panel, do not hesitate to contact a qualified electrician. Their expertise ensures the job is done safely and to code, protecting your home and your family. A correctly installed sub panel is an investment that adds value, functionality, and peace of mind for years to come.