Cummins · Cummins D6 Commercial Diesel

Cummins C300 D6

300 kW standby / 270 kW prime · Diesel · Liquid-cooled

300 kW EPA Tier 3 diesel standby generator with Cummins QSL9-G7 inline-6 engine and PowerCommand 2.3 control. HPCR fuel system, sound-attenuated enclosure, for large commercial and industrial standby applications.

Cummins Cummins C300 D6 generator — specifications and details
Standby power
300 kW / 270 kW prime
Voltage options
120/208V, 277/480V, 347/600V
Frequency / Phase
60 Hz · 3-phase
Engine
Cummins QSL9-G7 · 8.8L
EPA / Emissions
Tier 3
Commerciallight-industrialData Centers
Configure & QuoteDownload spec sheet

Overview#

The Cummins C300 D6 (model designation DQDAC) is a 300 kW standby diesel generator set built on the QSL9-G7 engine -- an 8.8-liter, inline-6-cylinder turbocharged and charge-air-cooled industrial diesel running at 1800 rpm. Rated at 375 kVA standby and 338 kVA prime at 60 Hz, the DQDAC represents the maximum standby output of the QSL9-G7 engine platform. It also carries a DCC (data center continuous) rating of 680 kW / 850 kVA.

Standard equipment includes the PowerCommand 2.3 control with AmpSentry protective relay, an HCI434F alternator, and a sound-attenuated enclosure. The engine features Bosch high-pressure common rail (HPCR) fuel injection, a Holset HX40 wastegated turbocharger, and a 24-valve cylinder head design. EPA Tier 3 certified.

The DQDAC is the top of the QSL9 standby range. For applications requiring more than 300 kW, the next step up is the C350D6 which moves to the larger QSG12-G1 engine platform (11.8L). The DQDAC is designed for large commercial, healthcare, and data center standby applications.

Our Service Experience#

At 300 kW, the QSL9-G7 is operating at its maximum standby rating. This means the engine has less thermal headroom compared to the 250 kW DQDAA on the same block. We recommend more frequent charge air cooler inspections and turbocharger monitoring on DQDAC units. The HPCR fuel injection system is paramount -- any fuel contamination at these power levels will manifest as injector faults and rough running more quickly than on lower-rated QSL9 applications. We keep a close eye on fuel pressure trends during annual load bank testing.

Frequently Asked Questions#

What fuel consumption should I expect from the DQDAC? Based on the QSL9-G7 engine spec sheet, standby fuel consumption at full 300 kW load is approximately 23.5 gallons per hour (89 L/hr). At 50% load, consumption drops to approximately 12.7 gallons per hour (48 L/hr). These are verified from the Cummins engine specification sheet.

Can the C300 D6 be paralleled? Yes. The PowerCommand 2.3 control supports paralleling with synchronizer and isochronous load sharing. Multi-unit paralleling of DQDAC generators is common in hospital and data center applications.

What alternator does the DQDAC use? The DQDAC uses the HCI434F alternator as standard equipment. This is a brushless, 4-pole, drip-proof, revolving field alternator with Class H insulation.

Engineering specifications

Physical

Length
155 in
Width
56 in
Height
72 in
Dry weight
5,900 lb

Fuel system & runtime

Fuel use @ full load
23.5 GPH
Fuel use @ 50% load
12.7 GPH

Documents & downloads

Spec sheets & manuals

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Estimate runtime for the Cummins C300 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

11.0 hours(0.5 days)

Fuel consumption ≈ 18.13 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 C300 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 500 hours
Fuel filter
Every 500 hours
Major overhaul
≈ 25,000 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
HPCR fuel injection systemInjector fault codes, rough running, power loss, fuel dilution of oil—severe
Fleetguard two-stage fuel filterFilter clogging, reduced fuel flow, hard start under load—moderate
Charge air coolerCoolant in intake, white smoke, loss of power on high-load events—severe
Holset HX40 turbocharger bearingIncreased turbo noise, oil consumption, reduced boost pressure—moderate
PowerCommand 2.3 AmpSentry relayNuisance overcurrent trips during motor-starting events—moderate

Frequently Asked Questions

What engine does the Cummins C300 D6 use?
The Cummins 300 kW diesel generator (model DQDAC) uses the QSL9-G7, an 8.8-liter, inline-6-cylinder, turbocharged and charge-air-cooled diesel rated at 1800 rpm. EPA Tier 3 certified. The QSL9-G7 features Bosch high-pressure common rail (HPCR) fuel injection, a Holset HX40 wastegated turbocharger, and a 24-valve cylinder head. At 300 kW, the DQDAC is the maximum standby rating on the QSL9-G7 engine.
What are the standby and prime ratings of the C300 D6?
Standby rating is 300 kW (375 kVA) at 60 Hz, 0.8 power factor. Prime rating is 270 kW (338 kVA). The DQDAC also carries a DCC rating of 680 kW (850 kVA). Both at 1800 rpm.
What is the model designation for the 300 kW Cummins diesel generator?
The 300 kW standby diesel generator is designated DQDAC in the Cummins North American product line. It uses the QSL9-G7 engine with an HCI434F alternator and PowerCommand 2.3 control system. The next step up is the C350D6, which moves to the larger QSG12 engine platform.
What are the service intervals for the C300 D6?
Oil and filter changes are due at 500 hours or 12 months, whichever comes first. Air filter and fuel filter replacement at 500-hour intervals. Coolant flush at 4,000 hours. Major overhaul interval is 25,000 hours under standard standby duty conditions.
How does the C300 D6 compare to the C350 D6?
The C300 D6 (DQDAC) uses the QSL9-G7 engine (8.8L, 6-cylinder) while the C350D6 uses the larger QSG12-G1 engine (11.8L, 6-cylinder). The QSL9 at 300 kW is at its maximum standby rating. The QSG12 at 350 kW has more thermal headroom. If you need more than 300 kW or want a more conservatively loaded engine, the C350D6 is the next step.
Can OnPoint Generators service the C300 D6 in Northern California?
Yes. OnPoint Generators serves the San Francisco Bay Area, Silicon Valley, and broader Northern California with authorized Cummins service. We carry QSL9 parts, InPower diagnostic tooling, and provide annual maintenance, load bank testing, and emergency response for 300 kW installations.

Compatible equipment

Transfer switches

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