Wiring Schematics and Generator Sizing
|Emerson 2-71gm Genset Wiring Schematics pdf format|
|Please contact our service department for all technical questions:
Emerson 2-71gm generators 1-800-387-4972.
WITH A GENERATOR, SIZE MATTERS
The first thing you need to do is determine what size generator would work best for your particular
needs. When purchasing a generator, it’s important that you select one that’s capable of meeting
* You must match the rated output of the generator to the maximum anticipated power to be used.
WARNING: Electrocution, severe personal injury or death can occur: Do not connect any
generator to any building’s electrical system unless an isolation switch has been installed by an
electrician. Refer to the Generator Owner’s manual.
CAUTION: Property damage can occur: Do not connect any generator to any building’s electrical
system unless an isolation switch has been installed by a licensed electrician. Refer to the
Generator Owner’s manual.
TAKE IT STEP-BY-STEP
Follow these steps when determining your energy needs:
1. Identify the wattage requirements for the tools and appliances that you want to power. The power
requirements for the tool or appliance can be found on its identification plate or in the Owner’s
manual. If the power requirements are given in amps, multiply the amps times volts to derive the
2. Add up the required watts of all the tools and appliances you expect to operate simultaneously.
3. The total watts derived in step 2 is the size of generator you need. These three simple steps will
“size” a generator. Normally, you won’t need to consider motor starting requirements when using a
generator. When a generator is properly sized for a tool’s or appliance’s running requirements, surge
capability or 3 times the rated output for three seconds usually is sufficient to handle the motor’s
starting surge needs.
The Additional Guidelines section explains the procedures to calculate and size for motor starting.
This chart lets you immediately add up all of the appliances you will most likely utilize:
G E N E R A T O R W O R K S H E E T
|Furnace Fan, gas
or fuel oil furnace
|Central Air Condition|
|HEATING / COOLING
|Dish Washer – Cool Dry||700||1400|
|Dish Washer – Hot Dry||1450||1400|
|Clothes Dryer – Gas||700||1800|
|Clothes Dryer – Electric||5750||1800|
|Microwave Oven, 750W||750||800|
|Electric Range 6-in. Element||1500||0|
|Electric Range 8-in. Element||2100||0|
|Lights – Wattage||Actual:|
|Television – Black & White||100||0|
|Television – Color||300||0|
|Garage Door – 1/4 HP||550||1100|
|Garage Door – 1/3 HP||725||1400|
|Wet Pump – 1/3 HP||750||1400|
|Wet Pump – 1/2 HP||1000||2100|
|Sump Pump -1/3 HP||800||1300|
|Sump Pump – 1/2 HP||1050||2150|
|Vacuum Cleaner – Standard||800||0|
|Vacuum Cleaner – Deluxe||1100||0|
|Electric Weed Trimmer||500||500|
|Worm Drive Saw||1560||3100|
|12″ Concrete Cutter||1800||3600|
|7 1/4″ Circular Saw||1500||3000|
|Air Compressor, Average||2000||4000|
CONVERTING AMPS OR HORSEPOWER INTO WATTS
Horse Power required to start motor
If necessary, use these formulas:
Watts = Amps x Volts
Running Watts* = Horsepower x 932** (for motors)
HP * 2.4 amps = per leg requirement
Remember, this worksheet lists average power requirements — a particular manufacturer’s
device may use more or less than the listed wattage.
* Add a 10% correction factor to your totals to help overcome this uncertainty.
If your customer plans to operate devices that use electric motors, list both the starting and
running requirements of each.
* Starting requirements of some devices maybe significantly higher than their running
requirements. This higher demand must be considered when estimating your power needs.
Some small, universal motors — which do not draw a heavy starting load (drills, small saws,
blenders, etc.) — require very little extra current for starting.
When listing items that use motors, take them in the order of highest – to – lowest starting
requirements, as shown in the example below. Motor A, for instance, has a starting requirement
of 2,600 watts, so it’s listed first, followed by Motor B at 1,300 watts, and Motor C at 1,000 watts.
|MOTOR / DEVICE
Once you have compiled an accurate list of what you will be operating, you can calculate the
maximum power requirements. There are three different calculations you can make, depending
upon the kinds of tools and appliances on the list, and their intended use:
* No electric motors.
* One motor running at a time.
* More than one motor running at a time.
NO ELECTRIC MOTORS
If your list does not include any devices that use electric motors, simply add the power (running)
requirements of all the items on your list to obtain the maximum power needed.
* For example, if you intend to use only an electric skillet, a 100-watt light and a heating pad (as
shown below), the maximum power requirement would be 1,655 watts. In this case, a generator
that can produce 2,500 watts rated output, is recommended.
* Running Watts is the amount of power a motor consumes once it has started to run at normal
** 932 is the factor used to convert motor horsepower ratings to needed electrical energy. It takes
into account normal losses in utilizing that power.
The formula for voltage drop is: Vd = 2K x L x I / Cm
Vd = Voltage Drop
I = Current in Conductor (Amperes)
L = One way Length of Circuit
Cm = Cross Section Area of Conductor (Circular Mils)
K = Resistance in ohms of one circular mil foot of conductor
K = 12.9 for Copper Conductors @ 75 degrees C
K = 21.2 for Aluminum Conductors @ 75 degrees C
/ = Divided by
We will assume you are going to use copper conductors and your temperature is @ 75 degrees C.
Reasonable operating efficiency is achieved if the voltage drop of a feeder or a branch circuit is limited 3 percent. However, the total voltage drop of a branch circuit plus a feeder can reach 5% and still achieve reasonable operating efficiency (210.19(A)(1)FPN No. 4 or 215.2(A)(4)FPN No. 2).
8 AWG = 50 amps @ 75 degrees C = 16510 Cm
Vd = 2 x 12.9 x 377 x 50 / 1650 = 30 volts
30 volts / 24 volts = 0.125 = 12.5% = Not Acceptable
6 AWG = 65 amps @ 75 degrees C = 26240 Cm
Vd = 2 x 12.9 x 377 x 50 / 26240 = 19 volts
19 volts / 240 volts = 0.079 = 7.9% = Not Acceptable
4 AWG = 85 amps @ 75 degrees C = 41740 Cm
Vd = 2 x 12.9 x 377 x 50 / 41740 = 12 volts
12 volts / 240 volts = 0.05 = 5% + Not acceptable – This is not acceptable because the 5% voltage
drop is at your sub panel. If you were to run any wire beyond the sub panel, your voltage drop would
exceed 5%. We are assuming you are going to install a light and some receptacles.
3 AWG =100 amps @ 75 degrees C = 52620 Cm
Vd = 2x 12.9 x 377 x 50 / 52620 = 9 volts
9 volts / 240 volts = 0.038 = 3.8% = Acceptable
Your equipment grounding conductor (ground wire) is sized off of table 250.122. You need to run a
10 AWG equipment grounding conductor (ground wire).
Tip: Plan for voltage drop at 100 feet and increase one wire size for every 100 feet thereafter.
VOLTAGE DROP TABLE
|Wire Size Selection for Long Runs
|110 Volts, Single Phase, Max 3% Voltage Drop*
|220 Volt, Single Phase, Max 3% Voltage Drop*
* The table above applies to the single phase systems, in steel conduit, at a conductor operating
temperature of 75 degrees C. It assumes a power factor of one. The table may be used for
systems using non-steel conduit, but actual results for these conditions may result in a greater
** Type NMB cables may not be used for a 100 amp load.
*** Must use 6 gauge if using NMB or UFB.
WARNING! Installation of electrical wire can be hazardous, if done improperly, can result in
personal injury or property damage. For safe wiring practices, consult the National Electrical Code
and your local building inspector.