Cummins · Cummins D6 Commercial Diesel

Cummins C1250 D6

1250 kW standby / 1135 kW prime · Diesel · Liquid-cooled

1250 kW diesel standby generator with QSK38 37.7L V-12 engine and MCRS fuel injection. EPA Tier 2 compliant, PowerCommand control, 2P2L cooling, for data center, hospital, and mission-critical standby applications.

Cummins Cummins C1250 D6 generator — specifications and details
Standby power
1250 kW / 1135 kW prime
Voltage options
277/480V, 346/600V, 4160V, 12470V, 13800V
Frequency / Phase
60 Hz · 3-phase
Engine
Cummins QSK38 · 37.7L
EPA / Emissions
Tier 2
Data CentersHealthcareManufacturingCommercialparalleling-array
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Overview#

The Cummins C1250 D6 is a 1250 kW standby diesel generator set powered by the QSK38 -- a 37.7-liter, V-12 diesel engine with Cummins' Modular Common Rail System (MCRS) fuel injection. Rated at 1563 kVA standby and 1419 kVA prime at 60 Hz, the C1250 D6 represents the top of the QSK38 power band, delivering maximum output from this proven platform.

The QSK38 at 1250 kW provides 1.5+ MVA of apparent power in a single V-12 package -- a significant capability for data centers and hospital campuses that need above-megawatt standby. The MCRS fuel system, combined with the 2P2L cooling architecture, delivers precise fuel control and thermal management under the most demanding transient load conditions. The 40,000-hour major overhaul interval reflects the QSK38 platform's robust design.

Medium-voltage options up to 13,800V and PowerCommand 2.3/3.3 paralleling controllers enable multi-genset arrays for data centers requiring 5-15 MW of standby capacity. The C1250 D6 is commonly paralleled in arrays of 4-8 units for Tier III and Tier IV data center designs.

Engineering specifications

Physical

Length
155 in
Width
80 in
Height
92 in
Dry weight
13,500 lb

Fuel system & runtime

Fuel use @ full load
87 GPH
Fuel use @ 75% load
65 GPH
Fuel use @ 50% load
46 GPH

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Estimate runtime for the Cummins C1250 D6

Adjust load percent and tank size to estimate runtime. Pre-filled with this model's spec where available.

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Estimated runtime

3.0 hours(0.1 days)

Fuel consumption ≈ 67.11 GPH at 75% load. Estimate based on industry-typical 1800 RPM standby curves (≈0.07 GPH/kW at full load). Actual consumption varies by engine, ambient temperature, fuel quality, and tuning.

Service intervals

Manufacturer-recommended intervals for the Cummins C1250 D6 under standby duty. Field intervals may differ based on load profile, ambient conditions, and fuel quality.

Oil & filter
Every 500 hours or 12 months
Air filter
Every 1000 hours
Fuel filter
Every 500 hours
Major overhaul
≈ 40,000 hours

Common failure modes

What we've seen fail on this platform. Use as a service-planning reference, not a diagnostic — actual failure modes depend heavily on duty cycle and maintenance history.

ComponentSymptomTypical hoursSeverity
MCRS fuel injection systemInjector fault codes, rough running, power imbalance between banks—moderate
Turbocharger(s)Reduced boost, excessive smoke, turbo bearing noise—moderate
2P2L cooling systemCoolant temperature exceedances, system pressure loss in either loop—severe
Fuel quality / tank degradationFilter clogging, hard starting, injector fouling from stagnant fuel—moderate
Starting system (24V battery bank)Slow crank, failed start requirement on infrequently exercised units—minor

Frequently Asked Questions

What engine does the Cummins C1250 D6 use?
The C1250 D6 uses the Cummins QSK38 -- a 37.7-liter, V-12 diesel engine with Modular Common Rail System (MCRS) fuel injection. At 1250 kW, this is the top of the QSK38 power band in the D6 lineup.
What are the standby and prime ratings of the C1250 D6?
Standby rating is 1250 kW (1563 kVA) at 60 Hz, 0.8 power factor. Prime rating is 1135 kW (1419 kVA). Both at 1800 rpm, 60 Hz, three-phase.
What are the service intervals for the C1250 D6?
Oil and filter changes are due at 500 hours or 12 months. Air filter replacement at 1,000-hour intervals. Fuel filter at 500 hours. Coolant flush at 6,000 hours. Major overhaul interval is 40,000 hours under standard standby duty conditions.
How does the C1250 D6 compare to the C1500 D6?
The C1250 D6 uses the QSK38 (37.7L, V-12) while the C1500 D6 steps up to the QSK50 (50.3L, V-16) platform. The QSK50 is significantly larger and heavier, designed for the 1500 kW class. The QSK38 offers a more compact package for sites that can meet their load requirement at 1250 kW or through paralleling multiple C1250 D6 units.
What cooling system does the C1250 D6 use?
The C1250 D6 uses Cummins' 2P2L (2-pump, 2-loop) cooling system, which separates the jacket water circuit from the charge air cooling circuit. This provides precise temperature control and protects against thermal cycling damage during transient loads.
Can OnPoint Generators service the C1250 D6 in Northern California?
Yes. OnPoint Generators provides authorized Cummins service for large diesel generators across the San Francisco Bay Area and Northern California. QSK38 service requires Cummins INSITE diagnostics for MCRS fuel system calibration, and careful attention to the 2P2L cooling system.

Compatible equipment

Transfer switches

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