The term emergency power systems is often used as an umbrella for both emergency power and standby power systems. Both are on-site power sources that provide electricity to a building during grid outages or other failures of the normal supply. Although these systems are often referred to simply as “generators,” there is a meaningful distinction between emergency and standby systems.
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Emergency Power System Components
The primary components for both types of systems include the generator itself (power source), transfer equipment, controls, supervisory equipment, and accessory equipment needed to deliver power to selected circuits. They may be powered by a fuel supply or batteries.
The transfer switch is the device that shifts a building’s electrical load between the utility supply and the generator. When normal power is lost, it disconnects the utility and connects the generator to the building. Once utility service is restored, the transfer switch transfers the load back. Transfer switches may be automatic, delayed automatic, or manual, depending on the system design and code requirements.
Diesel is the most common fuel, but inspectors may also encounter natural gas, propane, or other alternatives. Biodiesel is an emerging renewable fuel compatible with most diesel generators, often requiring little or no modification, and supporting green building practices.
Emergency Power System Differences and Requirements
Emergency power systems are required by building and fire codes for life safety functions. Standby power systems are installed to support operational continuity or protect the property, but not necessarily human life.
The requirement for either system is generally determined by building and fire codes, which can vary based on occupancy type, facility use, critical functions, and the equipment being served. When an emergency power supply system is required by an AHJ, it usually specifies the class, type, and level of system needed.
NFPA 110: Standard for Emergency and Standby Power Systems explains these categories. Class is the minimum amount of time the system must operate at its rated load before refueling or recharging (minutes or hours). Type refers to how quickly the system must restore power after the normal source fails (seconds). Level indicates whether a failure would impact life safety (Level 1) or only continuity and operations (Level 2).
Much of this goes beyond what a commercial property inspector needs to know, aside from noting the presence of a system in the report. However, the following chart highlights key takeaways to help put observed equipment into context.
| Emergency Power System | Standby Power Systems | |
|---|---|---|
| Code Basis | Installed when electrical failure could cause injury or death (Level 1) | Installed when an outage would be disruptive or costly but not life-threatening (Level 2) |
| Examples | Exit signs, egress lighting, fire alarms, fire pumps, smoke control, evacuation elevators, emergency communications | Refrigeration, HVAC for comfort, data centers, manufacturing/industrial processes, communications, sewage disposal, non-life-safety lighting |
Level 1 emergency power systems are typically installed in buildings where lighting is necessary for safe egress and panic control in high-occupancy buildings, such as hotels, theaters, sports arenas, schools, and healthcare facilities.
A third category to note is the optional standby generator. These units are not required by code and are typically installed for discretionary measures (non-critical or life-threatening applications).
Building Inspection Video
The video below demonstrates inspection procedures for the generator and transfer switch for an emergency power system, outlines the scope in accordance with ComSOP Standards, and highlights visual points inspectors may choose to assess within or beyond the baseline scope.
The featured system was observed at a large recreational center. The label identifies it as a Kohler Power Systems diesel generator with Fast-Response controls. Whether it serves as an emergency generator or a standby generator depends on the connected loads and the building’s design intent.
To identify the type of equipment, inspectors should look for signage at the service entrance equipment. NEC Article 700 on Emergency Systems requires a sign at this location that indicates the type and location of any on-site emergency and legally required standby power systems, with specific exceptions for individual unit equipment.
Emergency Diesel Generator Inspection Checklist
The emergency power system inspection video highlights several key visual checks. Inspectors should look for signs of fuel leakage, verify clear working space around electrical equipment, and note exhaust outlets that could pose hazards if located near operable windows. The fuel fill may be visible at the unit, underground, or inside the enclosure.
Inside the building, the transfer switch is a critical component. It interconnects with the main electrical system, shutting off grid power when an outage is detected and switching over to generator power. Once utility service is restored, the transfer switch returns the building to normal power. The following checklist reviews inspection points in more detail, covering fuel supply, fire and life safety, and electrical components.
Inspecting generators is beyond the scope of ComSOP Standards, but commercial property inspectors should still understand the differences between emergency and standby systems, along with the basic requirements set by codes. While enforcement is handled by the Authority Having Jurisdiction (AHJ), inspectors can apply their general visual inspection practices to related components. This includes observing fuel storage, electrical equipment, fuel lines, and other fire and life safety considerations that may impact building operations and safety.
Additional Resources for Commercial Property Inspectors:
- Inspecting Commercial Electrical Systems Online Course
- Life Safety Inspection Online Course for Commercial Property Inspectors
- Mock Commercial Inspection Online Course: On-Site Inspection Procedures
- Mock Commercial Inspection Course: Pre-Inspection to Final Report Business Practices
- Commercial Property Inspection Checklists and Field Guides
- Commercial Property Inspection Video Library