What Size of Generator Do I Need For A 200AMP Service?

Even if you don’t plan on wiring your own home, learning about electricity is a great idea. It would help if you had at least a basic understanding of how electricity flows through your home, and knowing some electrical codes is also crucial.

As a result, knowing what size of generator do I need for a 200AMP service during an outage takes a bit more knowledge than what most people possess.

Below we’ll discuss some basic principles of electricity that can help you decide what size generator you need for a 200AMP service.

We will also cover measuring voltage which can be relatively handy in certain situations, such as checking whether or not an outlet works correctly. With that introduction out of the way, let’s get started.

Determining the Size of Generator Needed for 200AMP Service

What Size of Generator Do I Need For A 200AMP Service?There are two ways to determine how big a generator you will need for your application. You can either use watts to calculate or amps.

In all cases, for a given load, it is always more efficient to operate at lower watts rather than higher watts. In other words, it would be better to have a 1,000-watt generator and power 400 watts than a 2,000-watt generator and power 1,000 watts.

1. Using Watts Method

To determine what size of generator is right for your Service using this method, you need to know two things. What amount of watts does your home consume each hour, and what is the standby wattage requirement. Calculating both of these figures will give you a good starting point for finding out how big a generator you’ll need.

So, what is Wattage?

It refers to how much electricity your household is using each hour. You can find the watts on your utility bill at what’s called kWh usage. You can calculate Wattage by multiplying volts times amps (W=V *A). To convert from watts to kilowatts, multiply by 1,000. A kilowatt is equal to 1 amp at 1 volt.

Check out this video

On average American home uses about 11,000kwh of energy per month. So it would make sense to find out how much energy you are using in one hour (Watts Used Per Hour). Just divide your monthly number by 30 or the days in that month.

Calculating Wattage

What Size of Generator Do I Need For A 200AMP Service?For example, if your monthly bill shows 17,500 kilowatt-hours, to get that number down to usable hourly power use, divide 17,500 by 30. That brings it back down to 575 kilowatts, which gives 600 kw/h or 60360 total watts when rounded up.

Now we have our first information to calculate the overall power needs. The next part is determining your Standby Wattage Requirement.

Calculating Standby Wattage Requirement

When you turn off everything in your house, you need to figure out how much power you need. These include appliances, lights, and pumps except any items required for heating, such as wood-burning stoves and heaters plus fridges & freezers.

Check out this video

Though switched off, they still consume some power, but not nearly enough to compare to on levels.

The best way to determine your Standby Wattage Requirement is to take inventory of everything currently being used around your home and combine them into one lump sum. Here’s a quick table list of typical standby power drains:

The Amperage of Various Appliances & Devices that be serviced by 200AMP Generator

  Name Model Amperage
1. Electric Water Heater 1,500W 8 AMP
2. Washer Dryer Combo Units 1,300W 7 AMP
3. Range Hood 2,000W 10 AMP
4. Refrigerator 500W 8 AMP
5. Garage Door Opener 3,000W 27 AMP


In addition, lights around the house, including ceiling fans, chandeliers, and exit signs, account for 10-20% of your current load. With everything else turned off and only those items left running, you’re likely looking at around 300W.

However, these numbers might vary depending on home size and square footage.

Therefore, if you want to power 200AMP Service, you’ll first need to determine how many amps each item will use individually, then add up all of those numbers together.

In our example above, that would be 60 amps. After determining how much electricity your items will consume at one time, you can divide that number by 120 to determine how many watts it will be (to convert from amps to watts).

So, 60 divided by 120 = 7,200 watts

Then multiply that number by 0.8, about 20% for line loss and system efficiency factors. This means that, on average, your generator will only have to produce enough energy for 80% or 5760 or 5.8 kW to support 60 amp service.

2. Method 2 – Using Amperage

Amperage is best understood as how much current is moving through a wire or circuit at any given time. To determine how much you need for your home, you’ll first want to know what size of generator you need for your specific needs.

Let’s do some maths. First, let’s say you have a main breaker panel on my house that has ten circuits with thirty-five plugs spread across those ten breakers. We know that each circuit uses an average of 15 amps. So if you turned on all 35 appliances, the results should be as follows; 10 x 15 = 150 total amps.

That would require an 18,000 watt / 150 amp generator. But that’s not considering appliances like well pumps, central air units, and other such items that may be on separate circuits.

We also cannot forget about safety; when using extensive tools or high-powered machines, we recommend that you add another 20% to your calculations. With these considerations in mind, a 36,000 watt/200 amp generator should suffice in my case.

Frequently Asked Questions

1. How big of a generator do I need for a 200-amp service?

Depending on how many appliances you need to run, the generator required to power a 200-amp service should be between15kW to 20 kW. For example, if you have only one air conditioner running, you will need a 15kW generator.

On the other hand, if you have several large appliances like a refrigerator, sump pump, and water heater, you will need a 20kW generator.

2. Is there a 300-amp service?

The short answer is no; there isn’t. A residential building permit will not allow a more than 200-amp service run on a home. There are two reasons for that limit: first, it makes it safer for your electrician and other utility workers. Second, it helps prevent fires by keeping power from running through faulty wiring.

3. Is 200 amp enough?

It depends on how much power your home uses. Power requirements are measured in kilowatts, so you’ll first need to know your home’s peak usage. Most homes require a generator capable of at least 10-15 kilowatts, but larger houses may need more than that.

If you live in an area prone to extended power outages, get a big enough generator to handle all of your appliances. However, if losing power is a temporary inconvenience, you can downsize significantly without affecting performance or safety.

4. How many watts is 200-amp Service?

A 200-amp generator is at least 15,000 watts. To power your home at that level, you need to have an electric service of 15kW or more. The reason why it’s not just called 200 amps is that it takes a high voltage to get enough current out of an alternator to supply 15 kilowatts.

5. How much is a 200-amp generator?

The amount varies depending on the type of generator. For example, Kohler Generators RTX-JFNC-0200A-QS7 RTX 200 Amp Automatic Transfer Switch, Grey costs $659.40 while SIEMENS GNF324R 200 Amp, 3 Pole, 240-Volt, 3 Wire, Non-Fused, General Duty, Outdoor Rated costs $419.95.

6. What size generator do I need for the 400-amp Service?

You should have a 30kW to 50kW generator. This means you can keep using your appliances even during a power outage.

7. How many amps does a 4500-watt generator produce?

A 4500-watt generator can produce approximately 37.5 amps at 120 volts and 18.7 at 240 volts. The load will vary depending on how many appliances run on that circuit. More than one appliance drawing more than 25 amps will cause your generator to overheat and trip its internal breaker.

8. How many amps is a 12kW generator?

A 12kW generator is equal to 12000 watts. Since Watt=Voltage * Amperage (current) it will generate 100amp at 120V (12000/120) and 50amp at 240 V (12000/240).

9. How many amps can a 200-amp service handle?

A 200-amp service can typically manage no more than 160 amps of load at a time. If your house requires electrical appliances and other components that will generate more than 160 amps, then you will need a larger generator to accommodate those loads.

10. Can you overload a 200-amp panel?

Do not overload your 200-amp panel with more than 160 amps of load at a time. Overloading may damage your breaker or wire, which could cause a fire or shock and burn. Overloading also causes excessive heat, increasing wear and tear on circuit breakers.

11. What is the difference between a 200 amp and a 400-amp service?

The 400-amp Service can handle more load or power larger circuits. A 400-amp service can deliver more than 20,000 watts, whereas a 200-amp service can only deliver up to 20,000 watts. Thus, 400-amp Service is recommended for homes with many large electrical appliances like electric heaters and multiple ovens.

12. How many breakers are allowed in a 200 amp panel?

A standard 200-amp service panel has two 120/240-volt 20-amp spaces. This means that you can use up to four breakers, two per side of your panel, with each breaker rated at 25 amps. If you need more circuits than that, you will have to hire an electrician to upgrade your panel.

13. How many watts is a 100-amp service?

If you’re wondering how many watts are in 100 amps, simply multiple amps by volts. When multiplying amps and volts to get watts, remember that 1 volt = 1 watt/amp. So, with 100 amps x 120 volts = 12,000 watts. This means that a 100-amp service would provide 12,000 watts of power.

14. Can I put a 200-amp breaker in a 200-amp panel?

Yes, you can put a 200-amp breaker in a 200-amp panel. You will need to ensure that your main breaker is either rated at 300 amps or will be overstressed and fail to work.

15. Should I use a transfer switch when operating my generator?

Yes, generators equipped with a transfer switch are advantageous because they allow you to start and operate without having to connect directly to your home’s wiring.

It is essential to use portable generators in areas with no electric outlets present or protect against power surges. Without proper protection, plugging your generator directly into an outlet can damage both it and your electrical system.

16. How many amps will a 5000-watt generator produce?

A 5000-watt generator will produce 5,000 watts of power. So 5,000 watts divided by 120 volts = 41.66 amps.

17. What does it mean if I have 240 volt/120-volt electrical outlets in my home?

Most houses have 120-volt outlets (the typical household electrical outlet) and 240-volt outlets. These work exactly like their 120-volt counterparts, but they require more current to power larger appliances.

A 240-volt outlet typically supplies 60 amps of current, while a 120-volt outlet can supply up to 15 amps of current, depending on what kind of circuit breaker you have installed in your home.

Final Thoughts

The right size generator is more important than people think. After all, you don’t want to order a 200 amp generator if the power source is only 100 amps.

It’s reasonable for homeowners to order generators without realizing they’re not big enough to handle their needs. With so many different sizes available on the market today, it’s hard to find the best fit for your needs.

However, as we’ve seen from this post, finding the right size isn’t as hard as you think. It all comes down to determining how much power you need and how long you will be without power.

About Steve Stuart

Steve Stuart is an electrical engineer who developed interest on generators during his school years. After school, he became a generator enthusiast. This is after encountering power supply problems at the area of residence where he lived. Power would be on and off and so food would go bad and the room heater would go off especially during winter. After trying the different generator brands for several years, Steve now provides information on the available brands and products in the market today. Based on his experience, he gives the do’s and the don’ts when it comes to generator use.

Leave a Comment