THE BASIC FACTS.
There are different types of backup power devices depending on their operation and source of energy. Portable electrical generators
) are designed to temporarily provide AC power by burning supplied fuels. This page will explain you how they work, what types are available, how to choose the right one and how to connect it. As the name implies, these devices are for stand alone (non-hardwired) applications. Homeowners normally use them to energize a few appliances via extension cords, although high-end models can power an entire home.
Besides home use, portable generators are utilized on construction sites and basically everywhere where the grid is not available. Currently, they are sold in the range of 500W to 20kW, which will fit most homeowners requirements. Their main advantages are they are generally cheaper than standby systems and may be used right away without the need of any special installation.
CHOOSING THE FUEL TYPE.
People tend to think about a portable generator as if it is a kind of generic device. In reality, it comes in various types, which we are going to discuss below. Depending on the design, genset's engine can run on gasoline, diesel, propane, or natural gas. Of course, each design has its advantages and disadvantages. So, let's go over the pros and cons. Most small models are powered by gasoline from the on-board tank- this is what makes these generators truly portable. However, this also results in a short run time- typically it is less than twelve hours per tankful. If you run such a device continuously at rated load you will need to shut it down several times a day for refueling. There are more expensive models that can be hooked up to an external fuel source (natural gas, LPG or diesel) and supply electricity for extended periods of time. They can be used as portable home generators.
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devices generally cost less than all other types. You can buy for example a basic gas model
for about $300. If you go by price alone, it may be a good choice. However this type has a major often ignored disadvantage
: when the grid is down or after a major natural disaster gasoline may not be available. To assure a backup electricity during an unexpected wide-spread blackout you would need to store at home a substantial supply of gasoline. Note that unstabilized unleaded gasoline has a 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. Assuming this is true, you would need to replace your emergency supply at least every other year. Alternatively, for a few hundred dollars practically every engine can be converted into a multi-fuel one with a third party conversion kit. Also note that a gasoline engine requires frequent maintenance, such as periodic oil changes as often as every 20 hours or so. Finally, if not properly maintained, it may have start up problems especially at cold weather due to gum deposits.
Portable diesel generators
are more efficient, more quite, have the longest engine's life, but not surprisingly are more expensive. Diesel is the least flammable fuel source and has longer shelf line, but it likewise may not be available during a blackout.
can be easily stored in large tanks, has practically unlimited shelf life, and besides natural gas is the only fuel that may be available during major power interruptions. Among all types, an LPG-powered genset will more likely start in extremely cold weather. That's why I believe it should be your first choice for portable emergency power.
There are also multi-fuel
devices that offer more options when one type of fuel is not available. Usually a simple adjustment is needed to switch from one type to another. Although they are quite pricey, they still cost less than standby systems
with the same wattage and you don't have to pay for the installation.
FEATURES and OPTIONS.
When choosing a genset, aside from rated wattage, type and price, there is a number of other features and accessories to consider. Most gensets will sound like a lawn mower. So-called quiet models normally cost more and are not available in high power range. And they are still noisy, although to a lesser degree. By the way, check if there are any noise restrictions in your neighborhood. Besides noise level, look for the following useful features: voltage regulator (AVR), electric start (in addition to manual recoil), OHV engine, twist-lock receptacles, and oil gauge. If you plan to use your device without a transfer switch, look for a built-in GFCI for additional safety. Since a typical model may weight several hundreds pounds, you may want to get a wheel kit- devices with wheels can be moved around by one person. If you need a clean sinusoidal voltage for sensitive electronics, consider inverter-generators
. Unfortunately, they are typically priced twice as high as regular ones. Finally, 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, here is a lesser-known detail: the portables are often advertised by their short-term starting watts rather than by continuous power. For more information see our portable gensets ratings
page which provides a comparison chart, reviews, features and prices.
Electrical outlets provided by a typical mid-power portable genset (ETQ TG32P12): 240/120V L14-30R, 120V L5-30R, and 5-20R duplex with GFCI.
HOW TO CONNECT.
The most common method of hooking up your AC loads is by using extension cords. The genset's control panel has several 120VAC outlets. You just plug regular 3-wire cables into these outlets and run them through open doors or windows to the appliances you want to power. Be sure to use heavy duty outdoor-rated cords. The required wire size depends on its length and the rated load current. As a rule of thumb, #12 AWG cord is sufficient for currents up to 20 amps. Models rated above 5 kW usually also provide a 120/240 output via their 30 or 50 amp 4-hole receptacle. In this case, instead of running individual cables, you may use a 4-wire extension cord
. It plugs into the high-current locking 120/240VAC receptacle of your generating set and provides several outlets on the other end. See my eBook
for pinouts of other connectors.
The cords method perhaps is your only option if you are looking for a quick solution. However your lights 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 and then connect to the cords. You would have to go through all these troubles every time you need to use a generator. This is something many people don't realize beforehand. A more convenient and safe method is to hook up your power source to the house via a transfer system
. It connects your house either to the genset or to the grid and prevents so-called backfeeding. Backfeeding can hurt anyone working on the power line or coming in contact with a wire and is illegal. A transfer switch also protects your device from damage if service restores while it is running. Once you wired the switch, all you need to do is roll out your genset from a storage and connect its high-current twist-lock to the inlet box
via a single cable. You can either buy such a ready-to-use generator cord or you can get a proper plug and a socket and build it by yourself. See the above pinout diagram of the outlet for the wiring of a single-phase 125/250V 30A 4-prong plug NEMA L14-30P. The hook-up via a transfer switch is safer and gives you more flexibility. However, obviously, it increases your cost and requires a professional installation. Also note, most guides and reviews won't tell you that a genset with GFCI will not work with a regular changeover panel. You may need to get a special 3-pole transfer device or otherwise disable the GFCI, which is not quite safe and is not recommended.
If in an emergency you really must connect a generator to a building wiring without a redundant switch, remember that for everyone's safety the main service disconnect should be flipped to the "OFF" position prior to connecting the genset. For more info see diagrams that show how to make a plug
for a dryer connection. Note however, that this method is NOT recommended for a number of reasons. First, you would need to turn the main circuit breaker off before you connect a genset, and disconnect it before turning the service back on. If you accidentally do not follow the "proper sequence", you will be backfeeding. Secondly, your main disconnect may not be rated for twice the line voltage (which may develop across it if you have AC voltage on both sides). Finally, using male-male cord is really dangerous.
PORTABLE GENERATORS SAFETY.
Your owner's manual of course will include the recommended safety rules. However you may want to know certain basic less obvious things in advance.
- Just like all engine containing devices, electric gensets should always be used OUTDOORS. You should locate them at least 15 feet away from the house to avoid carbon monoxide and fumes build up.
- A genset should never be connected directly into a wall outlet or your house unless it is isolated from the service lines.
- Most portable generators need to be protected from rain and snow.
For the prices on some of the best rated models from a leading online retailer, see our low-cost generators picks page linked above.
Below you will find comparison guides and reviews of various models, and additional resources you need to make a decision about the best portable generator for your application.