Video Overview

Learn how to inspect an emergency diesel generator and transfer switch through a step-by-step overview of its components and common deficiencies.

What Are Emergency Backup Generators?

Emergency backup generators are on-site power systems designed to keep critical building operations running during grid outages. They’re most often diesel-fueled, but can also run on natural gas, propane, or other fuels. Biodiesel is an emerging renewable replacement for diesel, as it is compatible with most existing diesel backup generator systems, often requiring minor or no system modifications. Diesel engines also handle heavy electrical loads more efficiently, making them ideal for powering emergency lighting, elevators, fire alarms, and other critical systems. For a deeper understanding, take the Commercial Electrical Systems Online Course.

Emergency backup generators are often required for:

Fire and life safety systems (emergency lighting, fire alarms, fire pumps, etc.)
Fire and life safety code-compliance (IFC, NFPA standards, and other local and federal adoptions)
Critical operations (elevators, communications, lighting, refrigeration, and other critical equipment, etc.)

You may find that in many commercial properties, the generator is installed to power emergency lighting and critical systems only, not the entire facility. This ensures that basic safety functions remain operational during a power failure. In the video, Rob notes the generator was set up strictly for emergency lighting and connected to a dedicated electrical panel inside the building. To learn more about inspecting commercial fire and life safety systems, take the self-paced Inspecting Commercial Fire and Life Safety Systems Online Course.

Major Components

Several of these components are highlighted as the inspector moves through the system, from the generator itself to the transfer switch inside the building. Each part plays a critical role in ensuring backup power is delivered safely and effectively during an outage. The primary components you may see on-site include:

Generator unit
Fuel storage tanks
Fuel piping
Shut-off valves or overfill alarms
Containment, controls, and safety
Transfer and operation systems

Inspection Considerations

While inspecting generators outside the baseline ComSOP scope, inspectors can perform several visual checks that help clients better understand their systems.

Fuel Systems

Most outdoor generators are powered by fuel oil stored in a basin or tank. Fuel tanks can be above ground (visible) or underground (not visible). Fuel oil leaks might occur due to aging hoses, loose fittings, corrosion, or overfilling. Common leak points include the containment basin, fuel lines, and fill areas. Inspect the generator’s perimeter and examine the containment basin for signs of leaks or staining. Look for signs of leaks or staining around these areas.

Clearance and Accessibility

Generators and their components must remain accessible for maintenance and emergency response. Installations should be free of obstructions such as storage, vegetation, or nearby utilities. Inspectors should confirm clear working space around the unit and its components, including access to control panels and fuel fill points.

Exhaust Outlet Location and Safety

Because generators produce combustion gases, exhaust outlets must discharge into open air and away from operable windows, doors, and air intakes. Confirm that exhaust outlets are directed safely outdoors, without risk of backdraft into the building. Note any exhaust configurations that present potential safety hazards.

Transfer Switch

After completing the exterior inspection, Rob proceeds inside to locate the transfer switch. The transfer switch shifts the building’s electrical load between the utility supply and the generator.

Operation overview:

When the building loses power, the transfer switch detects the outage and signals the generator to start.
The switch then disconnects the building from the utility and reroutes power from the generator to selected circuits.
When utility power returns, the switch shuts off the generator and reconnects the building to the main grid.

Inspectors are not expected to operate or test the switch, but should observe and document its location, condition, and labeling. A non-contact voltage tester may be used to confirm live components without physical contact.

Emergency Panel

Near the transfer switch, an electrical panel typically controls the systems backed up by the generator. Inspectors can perform a visual inspection in accordance with the ComSOP Standard’s electrical section and document the panel’s location, label, and observed visible condition in their report.

Common Issues

Although generator and emergency power system inspections are beyond the baseline scope, inspectors should be aware of the common issues to report and recommend further evaluation:

Absence of shut-off valves or isolation methods on tanks and lines
Corroded, damaged, or unsupported fuel piping
Use of improper materials for emergency vent lines (i.e., aluminum or plastic)
Improper storage of flammable or hazardous materials, or missing hazard signage
Evidence of leaks, spills, or inadequate secondary containment
Missing or illegible labels on systems, panels, or hazardous materials

Additional Resources for Commercial Property Inspectors:

Emergency Diesel Generator and Transfer Switch Inspection