When you decide to connect a portable or standby generator to your Aiken home, you need a safe, code-compliant way to feed generator power into your electrical panel without backfeeding the utility lines. Backfeeding, which occurs when generator power flows backward through the meter and onto the utility lines, is extremely dangerous. It can electrocute utility workers who are repairing downed lines, and it can damage your generator and your home's electrical system when utility power is restored.
There are two primary solutions for safely connecting a generator to your home: an interlock kit and a transfer switch. Both prevent backfeeding, both are code-compliant when properly installed, and both allow you to power your home's circuits through your existing electrical panel. But they work differently, cost differently, and are suited to different situations. Here is a detailed comparison to help Aiken homeowners make the right choice.
How a Generator Interlock Kit Works
A generator interlock kit is a mechanical device that mounts on your existing electrical panel. It consists of a metal plate that slides over the panel's breaker positions, physically preventing the main breaker and the generator breaker from being turned on at the same time. When the main breaker is on, the interlock plate blocks the generator breaker from being switched on. When the main breaker is turned off, the plate slides to allow the generator breaker to be turned on.
This mechanical interlock ensures that your home is never simultaneously connected to both utility power and generator power. It is a simple, elegant solution that uses the laws of physics rather than electronics to prevent backfeeding.
To use an interlock kit during a power outage, you follow these steps: turn off the main breaker, turn off all individual circuit breakers, slide the interlock plate to the generator position, start the generator, plug the generator into the power inlet box installed on the exterior of your home, turn on the generator breaker in the panel, and then selectively turn on individual circuit breakers one at a time, being careful not to exceed the generator's wattage capacity.
The key advantage of an interlock kit is that it gives you access to every circuit in your panel. You are not limited to a pre-selected subset of circuits. You choose which circuits to power based on your priorities at the time, and you can change your selection at any time by turning circuits on and off. If you want to run the well pump for 30 minutes, then switch to the oven for an hour, you have complete flexibility.
How a Transfer Switch Works
A transfer switch is a separate electrical device, installed next to or near your main panel, that has its own set of circuit breaker positions. During installation, the electrician selects a predetermined number of circuits from your main panel, typically 6 to 12 circuits, and reroutes them through the transfer switch. These are the circuits you have decided are most important during a power outage, such as the refrigerator, well pump, furnace, sump pump, and selected lighting and outlet circuits.
Transfer switches come in two types: manual and automatic. A manual transfer switch requires you to physically flip switches to transfer each circuit from utility power to generator power. An automatic transfer switch (ATS) detects when utility power is lost, signals the generator to start (for standby generators with auto-start capability), and automatically transfers the selected circuits to generator power. When utility power is restored, the ATS transfers the circuits back and signals the generator to shut down, all without any action from the homeowner.
The key advantage of a manual transfer switch is simplicity and predetermined circuit selection. You do not need to calculate loads or selectively manage breakers during an outage because the circuits were pre-selected and load-balanced during installation. The key advantage of an automatic transfer switch is hands-free operation, which is especially valuable if you travel frequently or want your home protected even when you are not there.
Cost Comparison
Cost is one of the biggest differentiators between these two options, and for many Aiken homeowners, it is the deciding factor.
Interlock kit. The interlock kit hardware costs between $50 and $150, depending on the panel manufacturer and model. A power inlet box, which mounts on the exterior wall and provides the connection point for the generator cord, costs $50 to $100. The generator cord itself costs $50 to $150 depending on length and amperage. Professional installation, including the inlet box, wiring, breaker, and interlock kit, typically runs $500 to $1,000 total. This makes the interlock kit the most affordable option for connecting a portable generator to your home.
Manual transfer switch. A manual transfer switch with 6 to 10 circuit positions costs $200 to $500 for the switch itself. Professional installation is more involved because each selected circuit must be rerouted from the main panel through the transfer switch. Total installed cost typically ranges from $1,000 to $2,500 depending on the number of circuits and the complexity of the installation.
Automatic transfer switch. An automatic transfer switch is the most expensive option, typically ranging from $2,500 to $5,000 or more installed, depending on the size and features. However, an ATS is usually paired with a permanently installed standby generator, and the ATS cost is often included in the overall generator installation package. When paired with a standby generator, the total system cost ranges from $5,000 to $15,000 or more depending on the generator size.
Code Requirements in Aiken, SC
Both interlock kits and transfer switches are permitted under the National Electrical Code and the South Carolina building code when properly installed. However, there are specific requirements that must be met for each option.
For interlock kits, the kit must be listed (UL or equivalent) for the specific panel manufacturer and model. Not all panels have listed interlock kits available. The installation must include a power inlet box, a dedicated generator breaker in the panel, and proper wiring between the inlet box and the panel. The interlock kit must prevent simultaneous operation of the main breaker and the generator breaker.
For transfer switches, the switch must be listed for the application and properly sized for the connected load. The installation must prevent any possibility of backfeeding. All circuits routed through the transfer switch must be properly identified and labeled.
Both installations require an electrical permit in Aiken, SC. Unity Power & Light handles permitting and inspection for all generator connection installations.
Safety Considerations
Both options are safe when properly installed and used correctly. However, they have different risk profiles during use.
An interlock kit requires the homeowner to manually manage the load during a power outage. You must turn off the main breaker before engaging the generator breaker, and you must selectively turn on circuits without exceeding the generator's capacity. If you turn on too many circuits simultaneously, the generator will be overloaded, which can trip the generator's internal breaker or damage the generator. This requires some knowledge of which circuits draw the most power and the discipline to manage them during a stressful situation.
A transfer switch, whether manual or automatic, eliminates the load management burden because the circuits were pre-selected and load-balanced during installation. The total load of the selected circuits is designed to fall within the generator's capacity, so overloading is unlikely under normal conditions. This makes transfer switches a better choice for homeowners who are less comfortable with electrical load management or who want a more automated solution.
One safety advantage of the interlock kit is that it gives you access to your full panel. If a critical circuit was not included in a transfer switch installation, and you did not anticipate needing it, you cannot power it during an outage without rewiring. With an interlock kit, you simply turn on that circuit's breaker (after turning off another to stay within the generator's capacity).
Which Option Is Right for You?
The best choice depends on your specific situation, budget, and comfort level. Here are some guidelines based on common scenarios we see in Aiken homes.
Choose an interlock kit if: you have a portable generator and want the most affordable way to connect it to your panel; you want access to every circuit in your panel rather than a pre-selected subset; you are comfortable with the manual process of managing circuits during an outage; and your generator is large enough to power your essential circuits but you want flexibility in choosing which circuits to run at any given time.
Choose a manual transfer switch if: you want a predetermined, load-balanced set of critical circuits that you can transfer to generator power without thinking about which circuits to turn on; you prefer a cleaner installation with a dedicated transfer switch panel next to your main panel; or your insurance company or personal preference favors a transfer switch over an interlock kit.
Choose an automatic transfer switch if: you are installing a permanently mounted standby generator; you want fully automatic backup power that activates without any action from you; you travel frequently and want your home protected even when you are not there; or you want the premium, hands-free backup power experience.
Next Steps
Unity Power & Light installs interlock kits, manual transfer switches, and automatic transfer switches for homeowners throughout Aiken, SC and the surrounding CSRA area. We help you evaluate your generator size, identify your critical circuits, and choose the connection method that best fits your needs and budget. Every installation is permitted, inspected, and done to current NEC standards.
If you already have a portable generator sitting in the garage with no safe way to connect it to your home, or if you are considering a standby generator installation, contact us for a consultation and estimate.