Generac · MD Series (Modular Diesel)

Generac MD400

400 kW standby / 360 kW prime · Diesel · Liquid-cooled

400 kW modular diesel standby generator system. Factory-paralleled configuration with Perkins 12.5L inline-6 engine for N+1 redundancy.

Standby power
400 kW / 360 kW prime
Voltage options
277/480V, 346/600V
Frequency / Phase
60 Hz · 3-phase
Engine
Perkins 12.5L · 12.5L
Alternator
Generac 520

Overview#

The Generac MD400 is a 400 kW modular diesel standby generator system powered by a Perkins 12.5-liter turbocharged and aftercooled inline-six engine. Part of Generac's Modular Power System (MPS) platform, the MD400 is factory-configured with integrated paralleling controls for plug-and-play scalability. Multiple MD400 units can be deployed together for N+1 or N+2 redundancy, and the system supports mixed configurations with other MD Series units to match evolving facility load requirements.

The modular approach simplifies logistics for facilities that cannot accommodate a single large genset. Individual units can be taken offline for maintenance without interrupting backup power, and capacity can be added incrementally as facility loads grow. At 400 kW per module, the MD400 is well-suited for campus environments and multi-building facilities that need distributed, redundant standby power.

Our Service Experience#

The MD400 shares the proven Perkins 12.5L platform with the SD400. In modular installations, paralleling controller calibration is critical during commissioning and at each annual service visit. We recommend staggered exercise schedules for each module to confirm independent load-carrying capability, along with regular parallel operation verification to ensure proper load sharing and synchronization across units.

Engineering specifications

Physical

Length
137.5 in
Width
57.6 in
Height
68 in
Dry weight
6,649 lb

Fuel system & runtime

Fuel use @ full load
27.8 GPH
Fuel use @ 75% load
23.1 GPH
Fuel use @ 50% load
16.7 GPH

Thermal & ventilation

Heat to coolant
1,067,520 BTU/hr
Exhaust flow
3,044 CFM
Exhaust temp
1256 °F
Combustion air
1,180 CFM
Ventilation air
18,685 CFM

Documents & downloads

Spec sheets & manuals

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Configure your Generac MD400

Lock the enclosure, fuel system, transfer switch, and add-ons — we'll confirm pricing, availability, and lead time within one business day. Prefer a free-form quote? That option is still here.

Estimate runtime for the Generac MD400

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

Estimate runtime on this tank

Estimated runtime

9.3 hours(0.4 days)

Fuel consumption ≈ 21.45 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 Generac MD400 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
Load bank test
Every 12 months

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
Fuel quality / degradationHard starting, filter clogging, reduced power output4,380+moderate
Paralleling controller synchronizationFailed sync, load sharing imbalance, hunting20,000+moderate
BatteryFailed to start, slow cranking8,760+minor

Frequently Asked Questions

What is the difference between the MD400 and the SD400?
The MD400 is a modular (factory-paralleled) system designed for scalable, redundant power architectures. It uses the same Perkins 12.5L engine as the SD400 but comes factory-configured with integrated paralleling controls, enabling plug-and-play expansion with additional MD units. The SD400 is a single-unit standalone generator at the same power rating. The modular approach provides N+1 redundancy, easier installation logistics, and the ability to service one unit while another continues operating.
What is the fuel consumption of the MD400?
The MD400 uses the same Perkins 12.5L engine as the SD400. At standby rating, fuel consumption is approximately 27.8 gallons per hour at full load per module.
What voltages are available?
The MD400 is available in three-phase configurations at 277/480V and 346/600V, both at 60 Hz.

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