Honeywell 6442 Manual To Operations page 24

Generator Sizing Instructions:
There is not a single correct sizing solution. Following are several methods that, when mixed
with good judgement, should result in an appropriately sized generator. Remember to consider
load growth, seasonality, and effects of starting motors.
As municipalities and states adopt the new 2011 NEC Electrical Code, there may be new sizing
requirements, spelled out in the code book, which the installation technician must follow. Always
check with the local inspection department to confirm which code cycle will affect your install.
Never add amps when sizing a generator. Convert amps to kW and add kW to determine
the required generator size. Power factors for various motor loads vary widely. Adding
amps without properly accounting for the power factor and/or mixing voltages will result in
improperly sizing the generator.
When motors start, they create a current surge that step loads the generator and creates a
voltage dip. After selecting a generator, reference the generator's surge capability using table 3.
Verify that voltage dip is adequate for the application. Most commercial applications should be
limited to about 15% voltage dip and residential applications should be limited to a 30% voltage
dip.
Some applications utilize an uninterruptible power supply (UPS) to back up critical loads. Please
read sizing guide for this load type.
Measurement Method
Use a clamp-on amp meter or power analyzer to measure facility load levels. Clamp each leg
separately and take the measurement during peak usage levels.
240V 1ø Applications: To determine peak usage in kW, add the highest amp readings from the
two legs, multiply by 120 and divide by 1,000.
(L1 + L2)120 / 1000
Size the generator 10 to 20% larger than the peak measured load.
3ø Applications: Add the peak amp readings from all three legs and divide by 3 to determine
peak amps. Multiply peak Amps by volts, multiply the result by 1.732 (square root of 3), then
divide by 1000 to convert amps to kW.
Peak Amps = (L1 + L2 + L3) / 3
kW = [(Peak amps x Volts) x 1.732] / 1000*
*Assumes power factor of 1.0
Size the generator 20 to 25% larger than the peak measured load.
Project Layout
24
Peak amps = _____________ Peak kW= _____________
Determining Existing Loads/Billing History Method
11
Many customers have a utility rate structure that has a peak demand charge. Using a year's
worth of electric bills, size the generator 25% larger than the largest peak demand.
Verify motor and UPS load compatibility.
Load Summation Method
1) Enter running kW for all motor loads (except the largest) expected to run during peak load
levels into table 6. Refer to table 1 for typical motor load sizes and electrical require-
ments.
2) Enter kW for all non-motor loads expected to run during peak load levels into table 7. Refer to
table 2 for typical residential loads and rules of thumb.
3) Add the running motor load kW, non-motor load kW, and the starting kW of the largest
motor load.
Motor load running total (minus largest motor):
Non-motor load total:
Starting load from largest cycling motor:
Total electrical loads:
Select generator: Commercial (add 20 to 25% to total kW)
Residential (add 10 to 20% to total kW)
4) Confirm that voltage dip is within acceptable limits by comparing motor LRA to generator surge
capability (see table #3).
5) Confirm UPS compatibility (see page 6).
System Capacity – Load Calculation
I
f the local municipality or state you are in has adopted the 2011 NEC Code, you may be
required to use this step. Article 702 of the 2011 NEC includes a new requirement for sizing
(702.4). If no other method for sizing is acceptable, sizing of the generator shall be made in
accordance with Article 220 of the NEC. The system capacity estimating sheet will guide you
through this process.
PMM Load Control Module
2011
The PMM Load Control Module is a 50 amp contact housed in a NEMA 3R enclosure
for indoor and outdoor installation applications. Through the use
of the PMM Modules in conjunction with any of the 100–400
amp Sync Smart Switches, household or business loads can be
intelligently managed enabling the use of a smaller, more efficient
generator system. Up to four PMM Modules can be used with a
single switch.
Ball Park Estimates (Do not use for final sizing)
Estimate based on 60% service size: (commercial)
240 Volts, 1 Ø: __________ Amps x .15 = __________ kW
208 Volts, 3 Ø: __________ Amps x .22 = __________ kW
240 Volts, 3 Ø: __________ Amps x .25 = __________ kW
480 Volts, 3 Ø: __________ Amps x .50 = __________ kW
Estimate based on 40% service size: (residential)
240 Volts, 1 Ø: __________ Amps x .10 = __________ kW
208 Volts, 3 Ø: __________ Amps x .15 = __________ kW
240 Volts, 3 Ø: __________ Amps x .17 = __________ kW
480 Volts, 3 Ø: __________ Amps x .34 = __________ kW
Estimate based on square footage
Fast food, convenience stores,
restaurants, grocery stores
Other commercial applications
Square footage = __________ Estimated kW = __________
220.87 NEC 20
Peak Demand = _______
_______________ kW (ref. table 8)
_______________ kW (ref. table 9)
_______________ kW (ref. table 8)
= ______________ kW
702.4 (B) (2) (a) NEC
kW = 50 kW + 10 watts/sq. ft.
kW = 30 kW + 5 watts/sq. ft.