This guide is designed to help you choose the right fixed automatic system for your home or business. It will tell you how standby generators operate, what types are available, and how to choose. You will also find here a quick review of major brands and the lesser known details you need to know.
HOW THEY WORK
All stationary on-grid power systems include three main parts: an engine- generator set (genset), a transfer system, and a control circuit.
The genset is always mounted outdoors. It has to be hardwired to a transfer system and connected to a fuel line, such as natural gas or liquefied propane (LPG). The transfer system is usually installed indoors and wired between the utility lines and main distribution panel. The control circuit is continuously monitoring the condition of the mains voltage. If the utility power is down or its voltage drops below a preset level, the control circuit starts up the generator. First it lets it warm up for certain time, typically from 5 seconds to 1 minute. Then it disconnects your house from utility lines and connects it to the generator. During the transfer time the device is powered from an external battery.
YOUR CONNECTION OPTIONS
There are two main stationary system configurations.
If wattage of the model you picked is sufficient to power the whole house, you can install a transfer system between the main service disconnect and your existing circuit panel. You transfer switch should have the same or greater amperage than the main circuit breaker. With this setup, you don’t have to rewire individual branches since you will be switching the entire service.
If you chose a system that is not large enough to run the whole house, you may need to install a sub-panel for critical lines desired to be energized in an emergency. Automatic transfer systems often come with a built-in sub-panel. You will need to re-wire the selected circuits from the main box to the sub-panel.
With the first option, you pay more for a larger generator, but you save on the installation costs since you don’t have to move individual circuits. With the second option, you save on the genset, but pay extra for the labor.
Nowadays many automatic models come with a digital load management (DLM) control. This technology lets you prioritize your appliances. If your system approaches its maximum capacity, the DLM starts shedding non-essential loads to prevent overload. This allows you to buy a smaller generator.
WHAT TO CHOOSE
There are a number of genset brands available on the market. The main domestic manufacturers of standby systems are Generac®, Kohler®, Briggs & Stratton, and Cummins® Onan®. As far as I know, Siemens, Eaton and Honeywell models are actually made by Generac. Likewise, GE and Milbank systems are manufactured by Briggs & Stratton. Each of these brands obviously has its pros and cons. Generac is the largest domestic manufacturer of home generators: in 2010, its market share was greater than 65%. It offers a broad selection of residential air-cooled stationary systems in the power range from 6kW to 22kW. Generac Guardian series seems to be on the low end of the price range. Kohler and GE seem to be a bit more expensive, but they offer long warranties. Of course, all warranties have some limitations- refer to official documents for complete information. Kohler claims the fastest transfer time- its units restore power within 10 seconds of an outage. The chart below compares selected models in the 14 to 17 kW range, which is the most popular size for small homes with a central a/c.
|Transfer switch||Online price|
|5873||Generac||17 kW||steel||3||Included 100A||$3,700|
|40303||Briggs & Stratton||15 kW||no info||4||71045 (100A)||$3,800|
|14RESL||Kohler||14 kW||corrosion-proof composite||5 years 2000 hours||Included 100A||$3,900|
|040330||GE||15 kW||galvanneal||5 years 1800 hours||Included 200A||$4,200|
The prices in the above chart represent the numbers I found online at the time of this review. Of course, the prices change frequently, but this chart will give you some ideas of how much you may need to pay for an automatic system. A professional installation may cost $2,000-6,000. Note that installation of a fixed system by yourself may void the manufacturer’s warranty and may violate local codes. In the above power range, Generac Guardian 5873 seems to have the lowest cost per kilowatt. This model once was the Consumers Digest Best Buy. However, if you live in a salt air coastal area, you may want to consider Kohler corrosion-proof device. Unfortunately, Briggs & Stratton specification does not state the material of their enclosure.
LESSER-KNOWN FACTS TO KNOW
- Maximum power with natural gas is 5-10% lower than that with propane. The advertised rating of most dual-fuel models (and the numbers in the above table) is for operation on propane.
- Rated wattage is normally given for 60 oC at sea level. In summer and at higher elevations the available output will be lower.
- All automatic systems require a battery which is usually not included in the set.
- Advertised warranty is for residential use. Read fine print for commercial warranty (if any).
- If you have an older gas meter, its capacity may not be sufficient for high-power models. In this case you will need to contact your gas provider to change your meter. They may charge you from $500 to several thousand dollars for such an upgrade. However, if you are also adding a regular appliance that brings your fuel consumption above the meter rating, some utilities may upgrade it for free.