Wiring/Sizing

Wiring Schematics and Generator Sizing

Emerson 2-71gm Genset Wiring Schematics pdf format

Phase versus Polarity 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
your requirements.

*   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
required watts.

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

RUNNING
WATTAGE REQUIREMENTS
ADDITIONAL STARTING
WATTAGE REQUIREMENTS
TOTALS
HEATING/COOLING:
Furnace Fan, gas
or fuel oil furnace
1/8 horsepower 300 500
1/6 horsepower 500 750
1/4 horsepower 600 1000
2/5 horsepower 700 1400
3/5 horsepower 875 2350
Central Air Condition
10,000 BTU 1500 2200
20,000 BTU 2500 3300
24,000 BTU 3800 4950
32,000 BTU 5000 6500
40,000 BTU 6000 6700
HEATING / COOLING
SUB-TOTAL:
KITCHEN
Refrigerator, Average 600 2200
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
Washing Machine 750 2300
Coffee Maker 850 0
Toaster 2-Slice 1100 0
Toaster 4-Slice 1650 0
Electric Skillet 1500 0
Electric Range 6-in. Element 1500 0
Electric Range 8-in. Element 2100 0
Freezer 2500 220
KITCHEN
SUB-TOTAL:
BATHROOM
Hair Dryer 800-1700 0
Curling Iron 1200 0
BATHROOM
SUB-TOTAL:
OTHER APPLIANCES
Lights – Wattage Actual:
VCR 50 0
Heating Pad 65 0
Radio 100 0
Television – Black & White 100 0
Television – Color 300 0
Dehumidifier 400 0
Electric Blanket 400 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
APPLIANCES
SUB-TOTAL:
COMMERCIAL PRODUCTS
1/4″  Drill 300 300
Jigsaw 300 300
Electric Weed Trimmer 500 500
Router 1000 1000
Belt Sander 1000 1000
Disc Sander 1200 1200
Chain Saw 1200 1200
Worm Drive Saw 1560 3100
12″ Concrete Cutter 1800 3600
7 1/4″ Circular Saw 1500 3000
Disc Grinder 2000 4000
Air Compressor, Average 2000 4000
COMMERCIAL PRODUCTS
SUB-TOTAL:
GRAND TOTAL:

ADDITIONAL GUIDELINES

CONVERTING AMPS OR HORSEPOWER INTO WATTS            

Horse Power required to start motor
If necessary, use these formulas:

Watts = Amps x Volts                                                                      

HP/1.341=KW Requirement

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
STARTING WATTS
RUNNING WATTS
Motor A 2600 850
Motor B 1300 600
Motor C 1000 750

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.

DEVICE
WATTS
Electric Skillet 1500
Light 100
Heating Pad 65
Total: 1665

Footnotes:
*   Running Watts is the amount of power a motor consumes once it has started to run at normal
speed.
**   932 is the factor used to convert motor horsepower ratings to needed electrical energy. It takes
into account normal losses in utilizing that power.

VOLTAGE DROP

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*
25′ 50′ 100′ 150′ 200′ Amp Load
Copper 14 12 8 6 6 15 AMP
Copper 12 10 8 6 4 20 AMP
Copper 10 8 6 4 3 30 AMP
Copper 3** 3** 1 2/0 3/0 100 AMP
Aluminum 2 2 2/0 4/0 300
MCM
100 AMP
Copper 3/0 3/0 3/0 MCM 350
MCM
200 AMP
Aluminum 4/0 4/0 300
MCM
400
MCM
600
MCM
200 AMP
220 Volt, Single Phase, Max 3% Voltage Drop*
Copper 14 14 12 10 8 15 AMP
Copper 12 12 10 8 8 20 AMP
Copper 10 10 8 6 6 30 AMP
Aluminum 8 8 6 4 4 30 AMP
Copper 8 8 8 6 4 40 AMP
Aluminum 8 8 4 3 40 AMP
Copper 8*** 8*** 6 4 50 AMP
6 6 4 3 50 AMP

* 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
voltage drop.
** 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.