Generac · MG Series (Modular Gaseous)

Generac MG400

400 kW standby / 360 kW prime · Natural Gas / LPG · Liquid-cooled

400 kW modular natural gas standby generator system. Factory-paralleled for N+1 redundancy.

Standby power
400 kW / 360 kW prime
Voltage options
277/480V, 346/600V
Frequency / Phase
60 Hz · 3-phase
Engine
Generac 21.9L V12 SI · 21.9L
Alternator
Generac K0400124Y21
CommercialManufacturingHealthcareData CentersGovernment
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Overview#

The Generac MG400 is a 400 kW modular natural gas generator rated at 400 kW / 500 kVA standby (360 kW / 450 kVA prime) at 60 Hz. It uses a Generac turbocharged 21.9L V12 spark-ignited engine and is built on the Modular Power System (MPS) platform with a Power Zone Pro Sync controller for factory-integrated paralleling. This configuration is well-suited for hospitals, data centers, and large commercial facilities. The MPS architecture enables N+1 redundancy configurations where multiple MG units operate in parallel.

Our Service Experience#

The MG400 uses the Generac 21.9L V12 at 400 kW (194 psi BMEP per the spec sheet), a moderate-to-high loading for this platform. Exhaust temperatures reach 1,297 F at rated output. With 12 spark plugs per unit, ignition maintenance is a significant service event. The Power Zone Pro Sync controller manages paralleling when multiple MG units are deployed. Gas supply infrastructure must be sized for the 4,620 CFH demand at full load.

Engineering specifications

Physical

Length
154.4 in
Width
71 in
Height
66.5 in
Dry weight
7,286 lb

Documents & downloads

Spec sheets & manuals

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Estimate runtime for the Generac MG400

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

Estimate runtime on this tank

Fuel demand at 75% load

4,200,000 BTU/hr≈ 4200.0 cf/min @ 1,000 BTU/cf

On utility natural gas the runtime is generally unlimited provided the supply line and meter can deliver this BTU/hr at the engine's required inlet pressure (typically 5–14" WC residential, up to 5 psi commercial). Confirm against the OEM's published fuel-pressure spec.

Service intervals

Manufacturer-recommended intervals for the Generac MG400 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
Spark plugs
Every 2000 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
Spark plugsMisfiring, rough running, reduced power output2,000+minor
Gas regulator / fuel trainUnstable speed, hard starting, fuel pressure faults15,000+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 MG400 and the SG400?
The MG400 is a 400 kW gaseous generator built on Generac's Modular Power System (MPS) platform using a turbocharged 21.9L V12 engine with factory-integrated paralleling capability. The SG400 uses the same 21.9L V12 engine platform but is configured as a standalone unit. The MG400's MPS architecture enables N+1 redundancy configurations and the ability to service one unit while others continue operating.
What fuel types does the MG400 support?
The MG400 supports both natural gas and liquid propane (LP/LPG). Natural gas is the most common fuel choice as it eliminates fuel storage requirements and provides unlimited runtime with utility gas service.
What voltages are available?
The MG400 supports three-phase configurations: 277/480V and 346/600V at 60 Hz.

Compatible equipment

Transfer switches

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