What Size Generator for 200 amp Service?

Selecting the right generator size is a crucial decision. In the United States, the average electrical service is 100 amp to 200 amp. Although a power outage is not typical, you could consider a portable generator to run your house in emergencies. But what is the right generator size for a 200 amp service?

If you have a 200 amp service, consider a 7000-watt to 20000-watt portable generator based on your need. If you live in a large house and want to run the furnace, central air, and other tools, you should go for a 15 kw+ portable generator. Running the necessary appliances, consider an under 10KW portable generator.

How many KW can a 200 amp service handle?

To determine the wattage required for a 200-amp electrical panel, consider the Voltage of the electrical service. In most residential applications in the United States and Canada, the standard Voltage is 120/240 volts.

To calculate the wattage for a 200-amp panel at 120/240 volts, you can use the following formula:

Wattage = Voltage x Amperage

Wattage = 240 volts x 200 amps

Wattage = 48,000 watts

So, for a 200-amp panel at 120/240 volts, you would need a capacity of 48,000 watts. This is the maximum load that the panel can handle at any given time. Remember that residential electrical panels are typically sized to provide some extra capacity for future expansion and to ensure the electrical system’s safety. So it’s not advisable to load the panel to its total capacity. It’s a good practice to leave some headroom for safety and to accommodate future electrical needs.

How Do You Size a Generator?

Sizing a generator properly is crucial to ensure it can meet your power needs during an outage without overloading or underutilizing the generator. Here’s a step-by-step guide on how to size a generator:

  • Determine Your Power Requirements: List all the essential electrical appliances and equipment you want to power during an outage. Include lights, refrigerators, heating or cooling systems, sump pumps, well pumps, and essential electronics.
  • Note each item’s wattage (or amps and volts) on your list. You can typically find this information on the appliance’s nameplate or in the user manual. If wattage isn’t listed, calculate it using the formula: Watts = Volts x Amps.
  • Group items into two categories: essential and non-essential. Important things are those you must power during an outage. In contrast, non-essential items can be left off or powered selectively.
  • Calculate Total Wattage: Add the wattage of all essential items on your list. This will give you the total wattage required to power these items simultaneously. Be sure to account for starting or surge power, which is higher than the running power for some appliances like refrigerators or air conditioners.
  • Apply a Safety Factor: It’s advisable to size your generator to handle more than just the essentials, especially if you have a large starting load or plan to add more items. A standard safety factor is 20% to 25%. Multiply your total essential wattage by 1.25 to account for this safety margin.
  • Choose the Right Generator Size: Look for a generator with a rated capacity (in watts) that matches or exceeds the total wattage calculated in the previous step. Generators come in various sizes, from portable units to standby generators.
  • If you plan to use the generator for emergency backup power for your home, consider a whole-house standby generator that can supply power to your main electrical panel.
  • Fuel Source and Budget: Consider the fuel source for your generator, such as gasoline, propane, natural gas, or diesel. Choose a generator that aligns with your preferred fuel source and availability.
  • Factor in your budget. Larger generators with higher capacity tend to be more expensive. Balance your power needs with your budget constraints.
  • Consult an Electrician or Generator Expert: For complex installations or if you’re unsure about your power requirements, it’s advisable to consult with a licensed electrician or generator expert. They can provide valuable insights and help you select the right generator size.

Remember that proper generator sizing is essential for safety and functionality. An undersized generator may overload and cause damage, while an oversized one can be inefficient and costly. Carefully assess your power needs and plan accordingly to ensure your generator meets your requirements during power outages.

What Size Transfer Switch Should You Use for Your 200 Amp Service? 

When selecting a transfer switch for a 200-amp electrical service, you should choose one that matches your service’s amperage rating. In this case, a 200-amp transfer switch is the appropriate choice. Here are some key considerations:

  1. Amp Rating: The transfer switch’s amp rating should match your service panel’s amperage rating. In your case, a 200-amp transfer switch is needed for a 200-amp service.
  •  Type of Transfer Switch:Whole-House: Consider a whole-house transfer switch if you want to back up your home during a power outage. This switch connects your main electrical panel to the generator and allows you to power all circuits in your house.
  •  Load Center: Opt for a load center or sub-panel transfer switch if you only want to power specific circuits or essential loads. This allows you to select which circuits receive power during an outage while keeping non-essential circuits disconnected.
  1.  Manual or Automatic: Transfer switches come in manual and automatic varieties. Automatic transfer switches (ATS) can detect a power outage and automatically switch to generator power without manual intervention. Manual transfer switches require you to physically switch between utility and generator power.
  2.  Generator Compatibility: Ensure that the transfer switch is compatible with your generator in terms of amperage and type of connection (e.g., 3-pole or 4-pole). It’s crucial to match the transfer switch and generator specifications.
  3.  Installation: Proper installation by a qualified electrician is essential for safety and functionality. An electrician will also ensure the transfer switch complies with local electrical codes.
  4.  Safety Considerations: Following safety guidelines and adhering to local electrical codes when installing a transfer switch is essential. Proper grounding and electrical connections are critical.
  5.  Budget: Transfer switch prices can vary depending on the brand, type, and features. Consider your budget when selecting a transfer switch, prioritizing quality and reliability.

For a 200-amp service, you should use a 200-amp transfer switch. Choosing between a whole-house or load center transfer switch depends on your backup power needs.

Additionally, consider whether you want an automatic or manual transfer control and ensure compatibility with your generator. Always consult with a licensed electrician to install and size the transfer switch to ensure it meets safety and code requirements.

alternative to transfer switch: Generator Interlock Kits

A Generator Interlock Kit is an alternative to a traditional transfer switch for safely connecting a generator to your home’s electrical panel. A Generator Interlock Kit is a cost-effective solution that prevents backfeeding between your generator and the utility power source.

It allows you to manually switch between utility and generator power while ensuring that both sources cannot be connected simultaneously. Here’s how it works:

Generator Interlock Kit:

  1. Kit Installation: A Generator Interlock Kit is typically installed on the electrical panel cover or inside the panel. The kit includes an interlock bracket, breaker retaining bracket, and associated hardware.
  2.  Interlock Mechanism: The interlock mechanism physically prevents specific breakers in the electrical panel from simultaneously being in the “ON” position.
  3.  Selective Power Source: With a Generator Interlock Kit, you can select whether you want to power your home from the utility grid or the generator. You do this by manually turning off the main breaker that connects to the utility power and then turning on the breaker that connects to the generator.
  4.  Safety: The interlock mechanism ensures that the utility and generator power cannot be connected simultaneously. This prevents dangerous backfeeding, where electricity from the generator flows back into the utility grid.
  5.  Manual Operation: Unlike an automatic transfer switch, which can automatically switch between power sources, a Generator Interlock Kit requires manual operation. You need to physically switch between the utility and generator sources.

The advantages of using a Generator Interlock Kit include:

  • Cost-effectiveness: Generator Interlock Kits are generally more affordable than automatic transfer switches.
  •  Simplicity: They are relatively easy to install and use.
  •  Safety: They provide a safe way to switch power sources and prevent backfeeding.

However, there are also some limitations:

  • Manual Operation: You must be present to switch between power sources, which might not be ideal during an extended outage.
  •  Limited Circuit Selection: Generator Interlock Kits may limit the number of circuits you can power during an outage compared to a whole-house transfer switch.

Before installing a Generator Interlock Kit, it’s important to check local electrical codes and regulations to ensure compliance. Additionally, it would help if you had the installation performed by a licensed electrician to ensure proper wiring and safety.

Choosing between a Generator Interlock Kit and a transfer switch depends on your specific needs, budget, and willingness to manually switch power sources during an outage.


Choosing the right generator size for your 200 amp service requires understanding your power needs, calculating your total load, and considering factors like generator type and fuel choice. With careful planning, you can ensure reliable power during any outage.

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Rayan is an engineer, lives in a farmhouse. He has a passion for electronics and alternative energy. He loves to share his thoughts with other people. That is why he started the blog.

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