Diesel generators are essential for providing reliable power in industrial, commercial, and remote applications. However, operators may occasionally encounter a low voltage alarm, which can cause unexpected shutdowns and disrupt operations. Understanding the common causes of this alarm and following proper troubleshooting steps is crucial to ensure stable performance and protect connected equipment. This guide explains the typical reasons for low voltage alarms on diesel generators and provides step-by-step instructions to diagnose and resolve the issue.

Possible Causes of Low Voltage Alarm

1. Excessive Load or High Starting Current

Motors or high-power equipment can draw 3–7 times the rated current during startup, causing a temporary voltage drop and triggering the alarm.

2. Insufficient Generator Capacity

If the connected load approaches or exceeds the generator’s rated capacity, voltage may drop when the load is applied.

3. Low Voltage Alarm Setting or Voltage Regulator Issue

Incorrect AVR settings or a high low-voltage alarm threshold may activate the protection unnecessarily.

4. Unbalanced Three-Phase Load

Uneven load distribution or incorrect wiring connections can result in voltage drop on one or more phases.

5. Load-Side Short Circuit or Ground Fault

Short circuits or grounding issues in the load or supply cables can cause a sudden current surge, leading to voltage drop and triggering the alarm.

6. Site Wiring or Connection Issues

Loose terminals, improper wiring, or incorrect connection between the generator and equipment may also cause abnormal voltage behavior.

Recommended Troubleshooting Steps

• ● Check the nameplate information and rated voltage of connected equipment.

• ● Measure generator voltage under no-load and load conditions to observe fluctuations.

• ● Confirm the load power and starting method of all connected devices.

• ● Inspect load cables and equipment for short circuits or grounding issues.

• ● Gradually connect the load to identify which equipment may trigger the alarm.

• ● Adjust the low voltage alarm setting on the generator controller if necessary.