What Size of a Generator is for 400-Amp Service

With the increasing cases of power outages in the United States, it is necessary for everyone to get a generator to back up their power supply. So, when the power goes out, they can start their generator. Of course, most of the equipment and appliances in homes are powered by electricity. That’s why a power failure has become unbearable, even for only some minutes.

Generators come in various sizes and capacities and you need to find out your power consumption before you can get a generator that can serve your home fully. Today, we want to answer the question – what size of a generator is for a 400-amp service?

We won’t just tell you the appropriate generator size, but we will also explain how to determine the size. In addition, we will answer several other frequently asked questions about upgrading your electrical system. So, without further ado, let’s get straight to business.

How Many Watts Do I Get for 400-Amp Service?

The answer to the question lies in this equation: Volts x Amps = Watts

The two standard voltages supplied by power outlets are either 120 volts or 240 volts. So, if your main supply outputs 120 volts, you will get the following wattage from a 400-amp service panel.

Volts x Amps = Watts

120 volts x 400 amps = 48,000 watts.

On the other hand, if your main supply outputs 240 volts, you will get the following wattage from a 400-amp service panel.

Volts x Amps = Watts

240 volts x 400 amps = 96,000 watts.

So, with a 400-amp service panel, you’ll get 48,000 – 96,000 watts.

What Size of a Generator is for 400- Amp Service?

Generators also have two standard voltages and they are 120 volts or 240 volts. In fact, some of them have outlets for both voltages. So, based on the calculations we made above, we can state categorically that you need a generator that can give out at least 48,000 watts or 48 kilowatts for 400-amp service.

However, you need to understand that the electrical panel has nothing to do with your generator. What you need to calculate is the total power consumption in your house. To calculate the total power consumption, some homeowners will list out all their electrical appliances and the power consumption of each of them.

This will lead to an inflated figure. This is because some appliances complement each other. You can’t switch on both of them at the same time.

For instance, you can’t switch on your heating unit and your air conditioners at the same time. You’ll always switch on one of them at the same given time. So, you need to list out complementing devices and pick the amperage required by the one that consumes more power. This is how to get a more accurate figure. This figure will guide your choice of generator.

How To Size a Generator Based on Amps?

After summing up all the total amperage for all your appliances, use this equation to get the right generator capacity – Volts x Amps = Watts

For illustration, let’s assume that your total amperage is 120 amps. Remember that generators have two standard voltages – 120 volts and 240 volts. Let’s pick 240 volts for this illustration.

Volts x Amps = Watts

240 volts x 120 amps = 28,800 watts.

For a total power consumption of 120 amps, you need a generator that can supply at least 28,800 watts.

What You Should Know Before Upgrading to 400-Amp Service?

While upgrading to a 400-amp service panel is a great idea, it may be overkill for you. Most homes are fine with only a 200-amp panel. What we are saying is that the higher the capacity, the more expensive an electrical panel will be. Hence, if you decide to purchase a 400-amp panel when a 200-amp service panel is enough for your electrical system, it means you are wasting money. You’re paying for an extra 200 amps that you don’t need, at least, yet.

You can’t just upgrade your electrical panel without upgrading your wire and your circuit breakers too. Your electrician should evaluate your wiring and circuit breakers to be sure that they can handle a 400-amp panel. If not, they should also be upgraded.


1. Efficiency

When you upgrade to a 400-amp service panel, your entire electrical system will run safely and more efficiently. There will be enough power for all your appliances. In fact, you may not need to upgrade your electrical panel in the next 10 years.

2. Safety

When a power surge occurs, it usually leads to an electrical fire if the electrical panel does not have extra capacity to accommodate the surge. With a 400-amp service panel, power surges are not likely to cause electrical fires because there will be enough room to accommodate the surge. This is why upgrading your service panel will make your home safer.

Also, when your wiring can no longer withstand the amount of power you consume in your house, the wires may start melting or burning. What makes matters worse is that the wires are inside the walls. As such, you may not have direct access to the burning wires. That’s why burning wires could wreak havoc in your home.

However, when you upgrade your wires, they are not likely to melt because they will be able to handle your power consumption.

3. Additional appliances

As time goes on, you’ll continue to install more electrical appliances in your home, and your power consumption will keep increasing. With a 400-amp panel, you won’t need to upgrade your service panel because of new electrical appliances, no matter how heavy they are.

Final Words

As explained above, there are several benefits of upgrading your service panel, but it is not enough to upgrade only your service panel. You need to also upgrade your wiring and circuit breakers because they may not be able to handle the higher-capacity electrical panel. Finally, if you intend to upgrade your electrical system, don’t d