Service Manual

Table Of Contents
6. Service 10-2019
114 A062J683 (Issue 1)Copyright © 2019 Cummins Inc.
For these products, generator set output power is equal to amperage multiplied
by line to line voltage; that is, power (Watts) = amperage x voltage (L-L). The
C17N6H generator set model is rated at 70.8 Amps, at 240 V Line to Line,
which is equal to a power of 17,000 Watts (70.8 A x 240 V). If the generator set
is operating at its rated elevation and temperature, and the voltage is reduced
from 240 to 230 volts, the amperage will increase from 70.8 to 73.9 if the load
on the generator set is identical. To verify generator set power output:
Using the equation power = amperage x voltage can help determine if the
generator set is functioning properly, or is not providing the expected
power. Using the voltage measured at the generator set mounted circuit
breaker, and the current through the load leads, you can calculate the power
produced by the generator set and compare that to what is expected to be
available. It may be difficult to determine the exact power output of the
generator set using the customer's connected load, because these loads are
seldom always on (heating and cooling loads typically cycle on and off, and
have a high initial starting power requirement). If required, a load bank can be
used to determine the full output power of the generator set. See the Model
Specifications for derate information.
Generator Set Derating Guidelines
Maximum wattage or maximum current are subject to and limited by such factors as
fuel BTU content, ambient temperature, elevation, engine power, etc. The starting
point for derate caused by elevation or temperature varies depending on the
generator set model. Full rated power is available at 15.5 °C (60 °F) at sea level.
See the Model Specifications section for generator set derating guidelines for all
models. The table below is an example of applying product derates for warmer
temperature and higher elevation.
TABLE 15. DERATE CALCULATION EXAMPLE*
Factor Values
Scenario
A C17N6H model generator set is located at 2750 ft above sea level and
the air temperature is 93 °F.
Generator Set
Rating
70.8 Amps x 240 Volts = 17,000 Watts
Elevation
Derate
Schedule*
3.5% per each 1000 ft over 1000 ft
Temperature
Derate
Schedule
3% per each 10 °F above 77 °F
Calculation Equation
Example
Calculation
Example
Result