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How to Select a Home Generator


Summary: Selecting and Sizing a Home Generator: How to rate a generator for your application requirements.This handy guide will help you understand generator ratings as it applies to your home generator project.
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Selecting a Home Generator for Your Application Requirements

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There are a wide variety of portable generators that are available for purchase, however selecting the right generator for your project will require considerations about the rating and size.

Some generators are more suitable than others for the basic requirements of your home, and generally, many lower priced generators are not suitable for a home.

Small sized generators with a lower power output may not have sufficient engine durability to power your house during an extended power outage, and poor power quality can damage expensive electronic devices such as home office equipment and furnace controls.

Selecting the Right Voltage and Power Output

For basic home electrical loads you may wish to consider a generator with a 4-Wire 120/240 Volt configuration and a maximum power rating of 50 amps. The typical power connection supplied with the generator is a L1450P straight receptacle.

Smaller size portable generators typically have a 30 amp rating with a L1430 locking receptacle, or a 20 amp rating with a L1420 locking receptacle.

When selecting a generator for your home be sure to consider the following features:

  • Voltage stabilization for sensitive electronic appliances.
  • Automatic voltage regulation of 5% or less.
  • Capability to start a well pump or other large electric motor loads.
  • Capacity for all the essential loads you wish to use.
  • Overhead valve engine, opposed to side-mounted valves.
  • Continuous rating between 4400 and 7200 watts.
  • Peak rating sufficient to start the largest electric motor to be used.
  • Low level oil safety shut down.
  • 4-Wire, 120/240 volt output.
  • A fuel type that is available or connected to the home such as natural gas or propane, rather than gasoline.

Home Generator Fuel Options

Portable generators have several fuel options including, gasoline, natural gas, or propane. Each of these fuel types have certain advantages and disadvantages.

Gasoline is tempting because it is readily available, however there are drawbacks associated with gasoline. For example, If gasoline is stored for a period of time it can lose its energy potential. Gasoline also has a tendency to "gum up" the engine's carburetor system, which can eventually cause starting problems. Finally, gasoline is a very hazardous fuel to store because it is a highly volatile liquid and its vapors can be ignited easily by a spark, flame, or other hot object.

Natural Gas
Natural gas is the fuel of choice whenever it is available. Natural gas is a clean burning fuel that does not require a storage tank. In addition, exhaust emissions are kept to a minimum, which is becoming increasingly important as new, stringent regulations continue to be passed. However, due to the lower energy content of natural gas, your generator maximum capacity may be reduced by approximately 20%.

Propane is very similar to natural gas and it is a great alternative if natural gas is not available in your area. Propane is nontoxic so it burns clean and it is not harmful to soil or water. However, propane does have it's drawbacks. You must store propane in an appropriate storage tank. Yet, when it comes to storing propane, it is much safer than other petroleum products because of its narrow range of flammability. Due to propane's lower energy content, your generator maximum capacity may be reduced by approximately 10%.

Home Generator Cord Connectors
Generators have various types of electrical connectors depending on the type of generator, the type of power provided, and the size of the generator.

Many electrical connectors that are only rated for 120 volt, or low amperage 240 volt are not appropriate for powering your home.

If you have an existing transfer switch or generator panel with a cord connection, then make sure to purchase a generator that has the same receptacle specifications.

Generators with Full Panel GFCI Protection (Ground Fault Circuit Interrupter) comply with OSHA inspections for job site usage, therefore these generators will not function when connected to the home or building main breaker box because of a neutral that is bonded to ground. When both the generator and the home or building breaker box contains a neutral bonded to ground, the generator's GFCI will open and outlets will not function.

Generators with a 30-Amp Rating
Generators with a 4-wire 120/240-volt outlet and a maximum rating of 30-amps are the standard which is found on most portable generators in the 5 to 7 kW size range.

Generators with a 20-Amp Rating
If the generator has a 4-wire 120/240-volt outlet rated at 20 amps it will have limited output capabilities for lights and small loads, however it will not be able to power home appliances.

Examples of Approved Methods for Connecting a Generator to a Home
Transfer Switch.
Circuit breaker linkage lockout system.
A cord with the same voltage and amperage rating as the generator receptacle.

If you connect electrical loads to your generator receptacle which exceed the amperage rating, the circuit breaker on the generator will trip off and may stall the generator. To restart your generator and restore the generator power you must first decrease the connected loads by switching off circuit breakers in the household breaker panel.

If you try and connect a higher rated receptacle such as a 50-amp receptacle found on many portable generators in the 10 to 12 kW size range, you will most likely trip a breaker within the generator unit. This breaker serves as a protection device to prevent permanent damage to the generator unit.

Appliance Usage Guide
When using any generator, you will need to know the power requirements of your home appliances. The following guide shows you the power needs of various household appliances, tools and equipment. For the exact power requirements you should consult your product's data plate or manual.

generator loads chart

The wattages presented in this table are estimates.
The actual wattage required for your appliances can be calculated.

Remember that 1kW = 1000 watts, 2kW = 2000 watts, etc.

Running Watts = Volts X Amps

Rule of thumb: Allow 2kW per Horse Power for appliances with motors.
Some motors require up to 3 times the running wattage to start.

Always use the starting wattage when calculating electrical load requirements for your generator. Select the appliances you want to operate and add the starting wattages together to determine if they can all be operated at the same time without exceeding the limits of your generator. Remember that circuit breakers usually control more than one appliance.

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  • Electrical Codes for Generator Installations
  • Generator Transfer switch Wiring Diagram
  • Wiring Methods for Installing Electrical Panels
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More about Selecting a Home Generator


Frequently Asked Questions

Electrical Question from Jeffrey

[ad#block]Question: I wish to wire a 7kw backup generator into my exterior home breaker panel. The power goes out several times a year for several hours at a time. Can I use a 2 pole breaker to get the generator on to the panel?
I have a L14P box attached to the breaker box. This feeds the breaker, albeit on the output of the breaker. When the utility feed into the 200amp up top goes dead, I turn this off. I plug in generator, turn on it’s 2 pole breaker and both legs are energized. I manage my load with normal breaker control.

Thank you,

This electrical question came from: Jeffrey, from Bedford, Texas

Dave’s Reply:
Thanks for your electrical question Jeffrey.
When connecting a generator to a home there must be an approved transfer switch device installed to prevent any possibility of electrical connection between the utility company and the generator.


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selecting generator - 1957