The Basics of Home Generators

Home Generators Defined

A home generator, simply stated, is a device that supplies electricity to residential customers during power outages. It typically provides enough capacity to support the use of essential appliances (e.g. air conditioners, heaters, refrigerators, and lights). Home generators work by converting mechanical energy into electrical energy by creating an alternating magnetic field through a coil that emanates from the spinning shaft of an engine. This type of system/process is typically referred to as an engine-generator set or genset.

How to Choose a Generator

Home generators are either portable or stationary and run on a variety of fuels (e.g. gasoline, diesel, natural gas or LPG):

• Though relatively inexpensive (4,000W set for $350), the portable gas models have short run times, require frequent refills of the gas tank throughout operation, and are not suitable for long-term application.
• Stationary (standby) sets provide continuous power (they are generally connected to an external source of fuel) and they are therefore better suited as a long-term power backup.
• Though some portable devices can also be fueled by external sources (i.e. provide extended run times), they still require additional effort in terms of connection and activation. Stationary sets are already connected to the residence and fuel source and can be started by a push of a button.
• An Automatic Stationary set offers the added advantage of activating based on a sense of a power outage. When power is restored, reconnect the residence to the utility lines and turn off the genset.
• Stationary sets also offer power levels significantly higher than portables, which combined with the considerations discussed above, make them the optimum (yet more expensive) choice in insuring against long-term emergencies.
• In terms of size, an average air-conditioned residence should consider a system rated between 14kW and 17kW.

In choosing among the various options, features and benefits of engine-generator sets, wattage and cost offer threshold criteria in narrowing down the choices, but further refinement requires consideration of the need for emergency power, the availability of fuel, safety and convenience.

Choice of Fuel

The primary determinant in selecting fuel is availability. Most residential generators can run on both natural gas and propane. If these residences are already supplied with natural gas (or if propane is readily available in the area), this type of fuel configuration is recommended. Key factors to consider in selecting a natural gas model include:

• Required gas pressure because occasionally higher pressure may be required to drive the generator than is typically available to the residence.
• Oftentimes, the utility company will be able to close any gap between the minimum fuel pressure specified by the genset manufacturer and that normally supplied by the utility. This will normally require the installation of a regulator along with a separate gas meter.

The ability to switch to propane is especially useful with a stationary natural gas system in cases where the gas supply is interrupted (i.e. usually brought about by a natural disaster).

The obvious option should natural gas not be available, is the installation of a large propane tank, requiring periodic refills; or a diesel engine. The diesel engine offers the most efficient and maintenance-free alternative, but tends to be the most expensive and may not be available during wide area blackouts (generally more appropriate for commercial applications).

Installation of Home Generators

Stationary gensets are mounted outdoors on a cement pad, preferably near a fuel source. The location for the pad should be flat and allow for adequate water drainage. Ventilation away from the doors and windows is necessary to prevent the entry of exhaust gases from entering the house.

Included in the connection of the genset to the house is a transfer switch, which prevents any back feeding into the utility lines, and protects the genset from damage by preventing the electric utility from providing voltage while the genset is running.

Actual installation should be done by a licensed electrician conversant with the specific requirements of the local electric utility and knowledgeable of the permitting requirements for large fuel tanks (if applicable). Further, the fuel pipe sizing, construction and layout of the system must comply with the requirements specified in NFPA 54 (for natural gas applications) and NFPA 58 (for liquid propane applications).