What Size Wire Should You Use to Feed a Subpanel in Your Garage?

When it comes to electrical installations, particularly in garages, selecting the right size wire to feed a subpanel is crucial for ensuring safety, efficiency, and compliance with local electrical codes. The decision on the appropriate wire gauge depends on several factors such as the subpanel amperage, the distance from your main panel, and the type of wire being used. This guide aims to provide you with the necessary information to make an informed choice.

Determining the Amperage

First, you need to determine the amperage of your subpanel. Common subpanel sizes are 60A, 100A, or 200A. Each of these amperage ratings requires specific wire gauge recommendations.

Wire Size Recommendations

60A Subpanel: Use 6 AWG copper wire, or 4 AWG aluminum wire. 100A Subpanel: Use 4 AWG copper wire, or 2 AWG aluminum wire. 200A Subpanel: Use 2 AWG copper wire, or 1/0 AWG aluminum wire.

Distance Considerations

While the wire size recommendations above are a good starting point, the distance from your main panel to the subpanel also plays a crucial role. If the run is longer than 100 feet, you may need to use a larger wire size to account for voltage drop. A general rule of thumb is to increase the wire size by one gauge for every 100 feet of run. For example, if your run is 200 feet, consider using 4 AWG copper wire instead of 6 AWG copper wire.

Choosing the Type of Wire

There are two main types of wire typically used for subpanel installations:

THHN/THWN: This type of wire is suitable for conduit installations and is available in various sizes. It is highly recommended for installations where the wire will be run through a conduit. NM-B: Also known as Romex, this type of wire is commonly used for indoor installations. It is bundled with its own jacket and is perfect for situations where the wire will be run through walls or along ceilings and floors.

Always ensure that the type of wire you choose complies with local codes and regulations. For instance, NM-B wire is not suitable for runs where the wire will be exposed to moisture, as it is not moisture-resistant.

Local Electrical Codes and Regulations

Local electrical codes can vary widely, and it’s essential to adhere to these regulations. They may have additional requirements or amendments that affect your installation. It’s best to consult your local electrical codes and regulations before starting any work. Failing to comply with these regulations can result in fines, safety hazards, and even legal issues. Here are some key points to consider:

Permits: Ensure that you have the necessary permits before starting the installation. Licensed Electrician: If you’re not confident in your ability to install the subpanel correctly, consider hiring a licensed electrician. They will have the expertise and knowledge to ensure your installation meets all safety standards and regulatory requirements. Margin of Safety: It’s advised not to exceed 80% of the amperage on the wire used. This margin ensures that the wire can handle the load without overheating.

Conclusion: While the wire size often depends on the amperage and distance, taking into account local electrical codes and regulations is critical. Always consult with a licensed electrician if you have any doubts about the installation. Proper planning and compliance with local codes can save you time, money, and potential safety hazards in the long run.