# What Size Generator For 400 Amp Service?

**A 400 Amps service panel is essential for commercial and industrial space mainly. It will indeed power up even the most electricity-hungry tools to help you run the large residential, industrial or commercial area. However, power shortage for an extended period can be detrimental for such gigantic 400 Amps service panels.**

It will lower productivity and cost you profit-loss. Thus, it would help if you always used a generator to backup the 400 Amps panels. The real question is, what size generator for 400 Amp service is suitable?

We talked with industry experts following it. Most electricity and generator experts recommended that you will need 35KW to 50KW of electricity supply from the generator for 400 Amps service. It will be helpful to run multiple large-scale machines or air conditioners efficiently.

**The key to choosing the right generator size for 400 Amps service is to look at its power production capacity.** Then, as you convert the electricity requirement of the service panel to KW, you can easily choose the right size for the generator. Also, you must know how many Amps the generator can deliver at what volts.

Contents

## Why Choosing The Right Generator Size Important For A 400 Amp Service?

A 400 Amp service pane is a large one by any means. You will see its use in large industrial and commercial spaces. Following it, this large service panel will link with the industry’s production capacity. So, load shedding is the last thing you will want here. One of the best ways to avoid such inconvenience is to back up the system with a large generator.

But, what size generator should you choose for the 400 Amp service?

For this, you will have to convert the Amp rating of the panel to the required KW. Also, you must know the generator’s capacity to deliver the electricity at the Amp rating.

**In this case, you should know that Amps=Watts/Volts. It means that the amps rating results from how many watts the machine needs dividing by the voltage of the supply line.**

For instance, a generator may have a 1500W load capacity. If it runs at 120Volts, its amps rating will be= 1500W/120Volts. So, a 1500W load capacity generator will have a 12.5Amps rating.

## What Size Generator For 400 Amps Service Is Preferable?

In the previous section, we discussed the importance of a suitable-sized generator. Also, we have shown you the calculation technique of the generator’s Amp rating. So, we will take this calculation system deeper to know which generator size is ideal for the 400 Amps service panel.

Most industrial appliances will run at 120 Volts as a standard. So, for this volt, you need to find the generator’s wattage capacity. We already know the generator will work with a 400 Amps rated service panel.

So, the calculation follows:

**Amps= Watt/ Volts**

**So, watt= amps X volts = 400X120**

**It is equivalent to 48000W or 48KW.**

As this calculation suggests, for a 400 Amps service panel, you will need around a 48KW generator. But, the service panel can’t work at its full-load capacity. It will lose 15% to 25% of its actual load, which results in 300 to 350 Amps of accurate rating. Thus, a 35KW generator can confidently back up the 400 Amps service panel.

## Steps to Calculate Your Generator Size You Need

Now, you know the generator size requirement for a 400 Amp service panel. Yet, you might be keen to know how much wattage you need for the generator in residential space. For this, you must count the number of devices you want to run with a generator. Then, you can add up the total wattage requirement of all these devices.

The steps are as follows:

Step 1: Enlisting the number of devices

Enlist all of the appliances you want to run during a power shortage. It should be straightforward because you will hardly run three to five devices during a power shortage. Ideally, you may run air conditioners, fans, lights, and freezers. So, write their name on a notebook or your smartphone.

### Step 2: Calculate the wattage consumption

Now, you must count the wattage requirement for all the devices you want to run during power cuts. For this, you will need the following facts:

**1. Wattage requirement of the device when it starts****2. Wattage requirement for running the device**

The 1st point is crucial because every device requires a higher wattage when it starts. It is higher than the running wattage requirement of the appliance. For instance, a refrigerator needs around 1500W to 2000W to start. But, it will consume only 300W to 700W to run.

So, you have to calculate both wattage requirements separately.

You should find the device’s starting and running electricity consumption from their user manual. So, you must read the user manual and know the electricity requirement precisely.

### Step 3: Add the wattage required to know the generator size

Once you have found the starting and running electricity requirement of all home appliances you wish to run, you have to add them separately. Once you have added all the devices’ electricity consumption, you have got to go.

The summation of the wattage requirement will suggest which generator is suitable for you. Now, you can go to the market to choose the right generator without confusion.

### What’s The Number of Amps Is A 20kW Generator?

A 20kW generator typically has wired for single-phase. It gives you 83 amps at 120 volts for every leg. So, this requires 90 amps pre-set circuit breaker. But, when it comes to 400 amps along with 240 volts, it’ll give you 96000 watts.

If you’re using a diesel generator, you have to ensure you’ll use a minimum of 30% of its total capacity. As a result, a generator with 80kW/100kVA will give you a 24kW.

You probably don’t want a generator that’s too large and heavier. For this reason, you have to study its load in an emergency. When you don’t give it enough loads, it may quickly provide you with all types of issues.

**Related Articles:**

- what size generator for 100 amp service?
- What size generator for 600 amp service?
- what size generator for 200 amp service?
- what size generator for 150 amp service?
- what size generator for 500 amp service?

**Conclusion**

That’s all about: what size generator for 400 amp service. Hopefully, you have got the answer that you’re looking for. So, the content summary is that you should use a 30 to 50 kW generator with a panel with 400 amps.

Determining the necessary electrical loads in your building is a simple way to select a generator. Indeed, you have to pick a generator that has rated 25% more than the devices you have calculated.

**Frequently Asked Questions (FAQs)**:

**How many watts is a 400 amp service?**

A 400 amp panel service is designed to power up large devices with massive electricity consumption. When the panel runs at full-load capacity, you can expect to get 20000W or more than that electricity requirement from the service panel

**What can you power with 400 amps?**

The 400 amps service panel is essential for larger residential projects. You can use it to power up sizeable central air conditioners, room heating systems, saunas, etc. So, it is ideal to meet the electrical requirement of a larger size with adequate performance.

### How do I determine the size of generator needed for a 400 amp service?

To determine the size of generator required for a 400 amp service, calculate the total wattage requirements by adding up the starting (surge) wattage of all appliances and devices, as well as any additional wattage needs. Choose a generator with a rated wattage capacity equal to or greater than this total wattage.

### Can I use multiple smaller generators to power a 400 amp service?

Yes, you can use multiple smaller generators to power a 400 amp service by installing a load management system or using individual generators for specific circuits. However, ensure that the combined wattage capacity of the generators meets or exceeds the total wattage requirements of the service panel.