One of the most basic necessities on a jobsite is the need for portable power. The demand for clean, reliable power has made Multiquip generators the most highly regarded brand in the equipment industry.
This handbook will cover basic electrical terminology and provide you with the necessary guidelines to help properly size a generator.
A generator converts mechanical energy into electrical energy.
Electricity is commonly described in terms of voltage, amperage and watts:
Voltage can be compared to the flow of water. There must be a difference in pressure in order for water to flow from one location to another.
In an electric circuit, if there is a pressure (voltage), and path provided, then electricity will flow (current) through the conductor. Voltage is the force that causes electricity to flow through wires, while current is the movement of electricity.
Direct Current (DC) is an electrical charge that flows in one direction through a circuit (figure 1). It is commonly used in consumer goods such as radios and automobiles. Dry cells and batteries are some other common sources of direct current.
A direct current source is marked with plus (+) and minus (-) symbols that indicate the direction of current flow in the circuit. The theory behind direct current holds that it flows from the positive (+) terminal, through the circuit and returns to the negative (-) terminal of the power source.
Alternating current (AC) changes its direction of flow at regular intervals and is found in all residential, commercial and industrial applications.
Utility companies generate electrical power at several thousand volts and send it hundreds of miles. It is converted to higher and lower values through transformers.
The rate at which alternating current changes direction determines its frequency. Each time the current goes one way and then the other way is called a cycle. Frequency is the number of cycles that occur in a single time period.
Frequency is also commonly referred to as Hertz (Hz) or CPS (cycles per seconds). One Hz is equal to one CPS. In the United States standard household current is 60 Hz while many foreign countries use 50 Hz current.
In the construction industry 180Hz “high-cycle” current is used to power certain concrete vibrators. Some aircraft and ships use 400Hz power. Figure 2 illustrates the relationship between alternating current and frequency.
Phase is a term applied to designate the circuits of an AC system. In the single-phase system, the voltages are in the same time phase in all parts of the system. In the three-phase system, the voltages are 120° apart.
Single-phase power (figure 3) can be transmitted by either a two-wire circuit or a three-wire circuit. The single-phase two wire method is the simplest and most commonly used. The voltage associated with this method is 120 VAC and is used to supply lamps, small motors, hand tools and appliances.
The single-phase three wire circuit is really two single-phase circuits with one wire in common. The voltage associated with this method is 240 VAC. This application is used where more power is required can can be supplied by the two wire system. Multiquip GA-Series generators produce this type of single-phase power.
power (figure 4) is transmitted by three hot wires with one ground. It is more versatile than single-phase power and is commonly used in industrial and commercial applications. One reason for this is a three-phase motor is easier to start and more efficient than a single-phase design. It is not used in residential applications.
Construction equipment typically uses either single phase or three phase motors. The contractor should specify the phase required for the job. MQ Power has a full line of generators that provide both single and three-phase power.
Gasoline-powered portable generators are rated in terms of maximum and continuous output.
Maximum output is the total wattage put out by the generator over a short period of time. Once the generator has been running for about 5 minutes the heat created by the machine will lower its electrical output.
Continuous output refers to the total wattage put out by the generator over a long period of time. Frequently referred to as rated output, it takes into account the effects of heat on generator efficiency. When sizing a generator, continuous output is more important than maximum output.
There is also a difference between starting amperage and running amperage. Starting amperage is the amount of amps required to start an electric motor. Running amperage is the amount of amps required to continuously run a motor.
The first thing you will need to do is determine what type of load your customer will be using with the generator. There are two types of loads resistive and inductive.
Resistive, or reactive, loads are devices that use a heating element and require the same amount of power to start as to run. Examples include light bulbs and appliances such as heaters, toasters, irons and skillets.
Inductive, or capacitive, loads are devices that use an electric motor and require more wattage for start up than continuous operation. Examples of inductive loads include concrete mixers, submersible pumps and air compressors.
Next, ask your customer to provide you with the voltage, amperage, and wattage of the tools that will be run off the generator. With this information you can easily determine the total wattage requirement of the equipment being used. This is accomplished by using the power formula.
Use this formula to size a generator to fit your customer’s needs.
Volts x Amps = Watts
The following example explains how to apply the power formula.
A customer calls looking for a generator to power a heater at his jobsite. Simply ask what the voltage and running amperage is and insert them into the formula. So, if he has a 120-volt heater that draws 4 amps . . .
120 Volts x 4.0 Amps = 480 Watts
You have determined that the heater will need 480 watts to operate. In this application the smallest Multiquip generator (GA2H5) would adequately fit his needs.
When sizing a generator, select a unit that has a continuous output equal to or greater than the total wattage requirement of the equipment. It is often a good idea to provide a little more power than what is actually required. This will give the contractor a little more versatility once he arrives on the jobsite. Often the customer may need to run more equipment than initially expected and will appreciate the extra power.
One – Use this method exclusively with resistance loads (heaters, light bulbs, toasters etc.). Simply total the wattage of all the items being powered by the generator. For example, let’s say you have a total of 29 light bulbs rated at 100 watts each. The total wattage is 2,900 watts (29 x 100 = 2,900). Select a GA36HA generator which puts out 3,200 continuous watts.
“Safety is everybody’s business,” so the old saying goes. This has probably never been truer than it is in today’s workplace. The rise in court cases involving accidents on the job has grown steadily in recent years. Many of these unfortunate accidents could be avoided by having a staff that is properly trained and capable of educating the customer on the potential hazards of operating a piece of equipment.
Following are some basic tips for safe operation. Please take the time to read your operator’s manual before using your generator.
Always remember a generator is a source of high, and potentially lethal, voltage. Never permit unqualified people—especially children—to operate a generator.
GA-Series generators are equipped with a ground fault circuit interrupter (GFCI) on their duplex 120V receptacle. A GFCI protects the tool operator by reacting to leakage current in excess of 5 milliamperes. It should be understood that they do not eliminate the risk of shock or electrocution. By design they will reduce the duration of an electrical shock and minimize the risk of electrocution
All Multiquip generators are equipped with a grounding terminal located on the base of the machine. This enables the operator to provide the machine with a proper earth ground. A copper rod must be driven 8 feet into the ground and attached to the lug with a wire having a minimum size of #8. If possible, complete the ground from the generator to the building’s ground source.
Two – For items such as drills and other power tools, take the total wattage and multiply it by two. These tools will typically require up to twice the power to start than run under load. As an example, it takes 1,300 watts (1.5KW) to run a 71⁄4” circular saw. Multiply the running wattage by two in order to obtain the total wattage (in this case 2,600 watts). Again, you would need a GA36HA generator.
Three – Equipment with bolted down motors (mixers, compressors etc.,) running wattage is generally multiplied by three. Some equipment such as submersible pumps may even require up to seven times the running amperage to start!
Note: The appendix of this handbook contains several charts to help you determine the wattage requirements for contractor and homeowner applications.
Altitude and temperature can have adverse effects on generator output. Let’s begin by looking at the effects of altitude. Gasoline powered gensets will decrease by 3.5% in power for each 1,000 feet of elevation above sea level.
Example: A 6 KW generator in Denver, CO
5,000 ft. elevation
3.5 x 5 =17.5% decrease
Maximum output is now 4,950 watts.
High temperatures can also decrease the efficiency of your generator by 1% for each 10° above 60° Fahrenheit.
Example: A 6 KW generator in Phoenix, AZ
It’s Labor Day weekend; the temperature is 120°
120° - 60° = 6 x 1 = 6% decrease
Maximum output is now 5,640 watts.
Now let’s see what happens when you combine high altitude and high temperature.
Example: 6 KW Generator in Denver, Colorado
Elevation: 5,000 ft. elevation
Temperature: 100° Fahrenheit.
Altitude: 3.5% x 5 =17.5% decrease
100° - 60° = 4 x 1 = 4% decrease
Total decrease = 21.5%
Maximum output is 4,710 watts.
Never operate the generator or handle any electrical equipment while standing in water, while barefoot, with wet hands, or in the rain. Doing so could result in serious injury or death.
Never provide a unit to a customer if it is not working properly. Maintain electrical cords in good condition and check for worn, bare or frayed wiring. If a problem is found, immediately tag the machine and return it to your service department for inspection.
Never operate the generator set in an explosive atmosphere or near combustible materials. An explosion or fire could result.
Always ensure the generator is operated in an area with adequate ventilation. Gasoline engines consume oxygen and produce DEADLY carbon monoxide fumes.
Please exercise common sense when operating a generator. Only a qualified electrician should perform any electrical wiring.
Too often the decision to buy a generator is based solely on the engine used to turn the alternator end. In a market flooded with look-alike generators powered by similar engines it becomes difficult to decide on the best generator for the job.
Remind your customer that all generators are not created equal and cover the features and benefits so the customer is informed before making their decision.
X = This type of motor is not normally used in this power range. For larger motors watts = hp x 932
Note: For pumps, air compressors, air conditioners, add at least 25% to starting wattage.
Extension cords also present another factor that should be considered when sizing a generator. Cables should be sized to allow for distance in length and amperage so that the voltage drop between the generator and point of usage is kept to a minimum. Use the chart below as a guide for determining the proper size and length of insulated copper wire extension cord.
* Estimated
**These items usually require slightly higher starting amperage.
* Estimated
**These items usually require slightly higher starting amperage.
