Introduction
DALI (Digital Addressable Lighting Interface) is one of the most widely used lighting control protocols in commercial lighting systems.
The DALI bus typically operates at a nominal voltage of around 16V DC. Because of this, it is often assumed that DALI can be treated as a SELV (Separated Extra-Low Voltage) circuit.
However, that assumption is not correct.
DALI is classified as FELV (Functional Extra-Low Voltage), and that distinction has important implications for how systems are designed, installed, and assessed.
SELV vs FELV — What’s the Difference?
Both SELV and FELV operate at extra-low voltages, but the key difference is how the circuit is protected from higher voltages.
SELV (Separated Extra-Low Voltage) systems are electrically separated from higher voltage circuits, typically through reinforced or double insulation. This level of separation ensures that, under normal conditions, accessible parts of the circuit do not present an electric shock risk.
FELV (Functional Extra-Low Voltage) systems also operate at low voltage, but they do not provide the same level of protection. The circuit may have a relationship to earth or to higher voltage systems, and therefore cannot be assumed to be safe to touch.
In simple terms:
- SELV → low voltage and electrically separated
- FELV → low voltage, but not necessarily separated
Why DALI is Classified as FELV
DALI is classified as FELV because the DALI circuit does not meet the requirements of a SELV system. While the operating voltage is low, the way DALI systems are implemented in real-world equipment means they cannot be treated as fully isolated, touch-safe circuits.
In practice, this comes down to several key factors:
- Isolation within devices is not to SELV requirements
Many DALI drivers and control devices include isolation between mains and the DALI interface. However, this isolation is typically functional and not designed to meet the reinforced or double insulation requirements of a SELV circuit. - The DALI bus may have a relationship to earth
The DALI line is not required to be electrically floating in the same way as a SELV circuit. Depending on the device design, it may be referenced or coupled to earth. - The system is designed for communication, not safety separation
DALI is a communication protocol. Its electrical characteristics are defined to ensure reliable signalling between devices, not to provide a fully isolated power system. - The electrical characteristics depend on the complete system
A DALI line typically connects multiple drivers, control devices, and interfaces. The behaviour of the circuit depends on all connected devices, not just a single component.
For these reasons, DALI cannot be assumed to provide the level of protection associated with SELV circuits and is therefore treated as FELV.
What This Means in Practice
The classification of DALI as FELV has practical implications that should be considered during system design and installation.
While the voltage is low, DALI wiring should not be treated as inherently safe to touch in the same way as a SELV circuit.
This means consideration needs to be given to:
- how the DALI circuit is routed and contained
- how it is separated from other circuits
- how it is integrated into luminaires and control devices
- whether any conductors may be accessible
These considerations become particularly important where DALI is integrated into shared systems such as track lighting, modular luminaires, or user-accessible control interfaces.
Where Confusion Commonly Occurs
The most common issue is the assumption that extra-low voltage automatically means SELV.
Because DALI typically operates at around 16V DC, it is often treated as if it were a fully isolated, touch-safe control circuit. This can lead to design decisions that do not properly account for accessibility, insulation, or system-level behaviour.
Another common misconception is that if individual components appear compliant, the system as a whole will also be compliant. In reality, the behaviour of a DALI system depends on how all components interact once installed.
Why This Matters for Designers and Specifiers
Understanding that DALI is FELV is not just a technical detail — it directly affects how lighting control systems should be designed and assessed.
This includes:
- ensuring appropriate protection against access to live parts
- confirming how circuits are separated within a system
- assessing compliance at a system level, not just component level
- understanding the implications for publicly accessible environments
These considerations ultimately influence compliance, safety, and project risk.
Conclusion
DALI is a robust and widely adopted lighting control protocol, but it should not be treated as a SELV circuit simply because it operates at a low voltage.
DALI is FELV, and must be understood and applied accordingly.
Recognising that distinction ensures that lighting control systems are designed correctly from the outset, reducing risk and avoiding compliance issues later in the project.
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