THE PORTABLE GENERATORS BUYING GUIDE

THE BASIC FACTS.

Frequent blackouts and growing awareness lead to increasing interest in backup power solutions. Portable generators (or gensets) are designed to temporarily supply AC power during the electrical outages or in locations where grid is not available. As the name implies, this type of devices is for stand alone (non-hardwired) applications. They are normally used to energize a few critical appliances via extension cords, although high-end models can power an entire home. Besides home use, portable generators are utilized on construction sites, farms, motor homes, recreation vehicles, and in camping trips. Currently, they are available for sale in the range of 500W to 17.5kW. Their main advantage is they are generally cheaper than home standby systems and may be used right away without any professional installation.

CHOOSING THE FUEL TYPE.

Depending on the design, genset's engine can run on gasoline, diesel, biodiesel, propane, or natural gas. Each type has its pros and cons. Most of the small models get fuel from the on-board tank- this is what makes generators portable. This results in a short run time- typically it is less than twelve hours per tankful before refueling. If you run these devices continuously at rated load you will need to shut them down several times a day to add the fuel. There are more expensive portable home generators that can be hooked up to an external fuel source (natural gas, LPG or diesel) and supply electricity for extended periods of time.
Gasoline-powered devices generally cost less than other types of gensets. You can buy for example a 4000W gas model for about $350. The main problem with this type is when the grid is down the gas pumps may not work. To assure a backup electricity during a wide-spread blackout you would need to store a substantial supply of stabilized gasoline. Note that unstabilized unleaded gasoline has very short shelf life- it can begin breaking down in about six months and will gum up the fuel system. Manufacturers of some stabilizers claim their products can extend gasoline shelf life to two years. So, you would need to replace your supply of stabilized gasoline at least every other year. Alternatively, for a few hundred dollars consumers can convert practically any gas engine into a multi-fuel one with a third party conversion kit. Note that if not properly maintained, a gasoline engine may have cold weather start up problems due to gum deposits. All gas engines also require frequent maintenance such as periodic oil, filter and spark plug changes.
Portable diesel generators are more efficient, more quite, have the longest engine's life, but generally are the most expensive. Diesel also is the least flammable fuel source and has longer than gasoline shelf line, but it likewise may not be available during a blackout.
Propane can be easily stored in large tanks, has practically unlimited shelf life, and besides natural gas is the only type of fuel normally available during wide spread outages.
There are also multi-fuel devices that offer more options when one type of fuel is not available. Usually a simple field adjustment is needed to switch from one type of fuel to another. Although they are pricey, they still cost less than a permanent system with the same wattage, and you also save on the electrical installation.

FEATURES and OPTIONS.

When choosing a genset, aside from rated power, type and cost, there is a number of features and accessories to consider. Cheap brands may sound like a lawn mower. So-called quiet models normally cost more, but they are still noisy. Check if there are any noise restrictions in your neighborhood. Besides low noise level, look for the following useful features: OHV engine, electric start (in addition to manual recoil), 30 or 50 A twist-lock receptacles, and oil gauge. If you plan to use your device without a transfer switch, look for GFCI for additional safety. Since a typical model may weight several hundreds pounds, also look for wheels kit- devices with wheels can be moved around by one person. If you need a clean sinusoidal voltage for sensitive electronics, consider the devices with inverter technology. Unfortunately, inverter-generators may cost typically twice more than regular gensets. For a peace of mind it is preferable to have a part that is listed with the Underwriter's Laboratory (UL) or FM, or a respective safety agency in your country. As for wattage, be aware that portables are often advertised by their short-term starting watts rathen than by continuous power. See our comparison chart for reviews, ratings, features and prices of some of best ranking models.

HOW TO CONNECT A PORTABLE GENERATOR.

The most common method of hooking up your AC loads is by using extension cords. You just plug the cords into your genset outlets and run them through an open door or window to the appliances you want to power. Be sure to use heavy duty outdoor-rated cords. You will need 3-wire cable for 120VAC outlets and a 4-wire cable for 120/240V. The required wire size depends on its length and the rated load current. As a rule of thumb, AWG #12 cord is sufficient for currents up to 20 A. Instead of running individual cables, you may use a 4-wire extension cord set that plugs into the high-current locking 120/240VAC receptacle of your generating set and provides several female outlets on the other end. Likewise, for a 120V locking outlet you can get a 3-wire cord splitter.
This method perhaps is your only option if you are looking for a quick solution. However your lights, boiler, central a/c and everything else that is directly connected to your house wiring will not be powered. You will need to figure out how to disconnect them one by one from the building wiring system and then connect to the extension cords. You would have to go through all these troubles every time you need to use a generator. A more convenient and safe method is to hook up your backup power device to the house system via a professionally installed transfer switch. Such a switch isolates genset from the grid and prevents power backfeeding into utility lines. Backfeeding can hurt anyone working on the power line or coming in contact with a wire and is illegal. It also protects your genset from damage if grid restores while it is running. Once you wired your system, all you need to do is roll out your backup source from a storage and connect it to the transfer box via a single power cable that plugs into high-current twist-lock receptacle. You can either get a ready to use generator cord or just buy a plug and a socket and build it by yourself. See the diagram below for the pinout of a single phase 120/240V 30A plug NEMA L14-30. The method with a transfer system is safer and gives you more flexibility. However it increases the cost of your setup and requires professional installation. Many guides and reviews also won't tell you that a regular transfer switch will cause problems if your model has both GFCI and internally grounded neutral. In this case you may need to get a special 3-pole device or otherwise disable GFCI. Anyway, for everyone's safety, be sure your electrician turns OFF the main circuit breaker BEFORE starting the installation.