What Generator Alarms Mean


What to do About Them

Based on NFPA 110, 2010 edition


Building codes specify the following shutdown alarms be included on your generator’s control panel:

  • Low oil pressure
    • If the oil pressure falls low enough that engine damage could result, it will shut down the engine.
      • Check the oil level and fill if necessary.
  • High engine temperature
    • When the engine temperature reaches a high enough level that damage could result, it will shut down.
      • Let the engine cool before you attempt a correction. Never check the coolant level until the engine is cool. See your operator’s manual for safety instruction.

After the engine has cooled, remove any restrictions to the cooling air flow. Check fan belts. Check to see if the coolant pump is leaking—look to see if coolant is dripping from it. Have a qualified engine mechanic check it out and clean the radiator core.

  • Overspeed
    • Generators are designed to shut down if the engine speed exceeds 10% of its rated speed. Not much you can do here except reset the alarm and restart.
  • Overcrank
    • The generator will go into overcrank if it runs through its cranking cycle without starting or if the cranking voltage drops below its preset level.
      • Check your fuel supply and try again.
  • Remote stop station
    • The building code requires a remote manual stop station. This should have an alarm contact that signals a fault light on the generator control panel. If this alarm is on, just check to make sure your emergency stop switch has not been operated. (See Find Your Generator Control Panel on the flowchart to find how to reset it also see my video How to Set Up a Generator Stop Station)

Building codes (NFPA 110) specify the following additional alarms be present and separate from shutdown alarms.

These alarms are warnings and do not necessarily shut the engine down:

  • Low oil pressure pre-alarm (Pre-alarms are only warnings. They do not shut you down).
  • High engine temperature pre-alarm
  • Low coolant level (may also shut down)
  • Low fuel level (or pressure if LPG on NG)
  • Generator suppling load
  • Control switch not in auto (includes generator and automatic transfer switch)
  • High battery voltage
  • Low battery voltage
  • Low cranking voltage (Measures the lowest voltage during cranking)
  • Battery charger AC fail
  • Lamp test (Just checks to see if the indicator lamps work, it may also reset the alarms on some models)
  • Air damper shutdown if appropriate (Shutdown)
    • Some engines, like Detroit Diesel, have an air damper on the intake manifold. This may need to be rest. It will prevent a start.

Additional alarms may also be present as follows. Some may be code requirements.

  • Low coolant level (Required)
    • If your system has a coolant leak, this alarm will prevent a start when the coolant drops below the level sensor.
  • Low engine temperature (Required)
    • This alarm will not lock the engine out; however, the generator may be hard to start due to cold temperatures. If you get it running, the light should go out after the coolant exceeds 600 F. Check and repair your coolant heater.

Note: The alarms I have listed are NFPA required. Other alarms may be present like “RPM Sensor Loss”. This is not a required alarm, but it will shut the machine down. The primary reason for this alarm is to create an expensive service call.

Alarms other than NFPA required alarms are essentially video games. Their purpose is marketing. They create confusion, expensive service calls, and improve a vendor’s profits.

“Auxiliary Fault” is also not a required alarm, but it may shut the machine down.

Remember to clear an alarm on most generators, turn the control switch to “Off” before pushing the “Reset” button. Otherwise, it won’t clear.

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