Understanding Safety-Related Electronic Circuits (SRECs) in UL 8750

03 Jun 2026

Why Functional Safety Matters More Than Ever

As lighting products continue to evolve, electronic controls are no longer simple on/off devices. Modern LED equipment increasingly relies on complex electronics and embedded firmware to manage critical safety functions. This shift has made functional safety a central concern in product certifications, particularly under UL 8750.  As a result, Supplement SA – safety-related electronic circuits (SRECs) exists.

This article provides a practical overview of when Supplement SA applies, what an SREC evaluation entails, and how manufacturers and safety engineers can navigate functional safety expectations with confidence.

From Electromechanical Controls to Functional Safety

Historically, many safety critical functions in lighting products were handled by electromechanical devices such as bimetal thermostats, switches, etc. These components directly controlled loads, and their safety could often be verified through prescriptive testing alone (i.e., UL 873, UL 60730-2-9).

In present day, products are more complex. Electronic circuits utilize logic-level signals, sometimes relying on microcontrollers with embedded software/firmware, often making decisions that are relied upon to mitigate hazards. When electronics or software are responsible for preventing fire, electric shock, or injury to persons, correct operation can no longer be assumed – it must be evaluated. This is where Supplement SA becomes applicable.

When Does UL 8750 Supplement SA Apply?

UL 8750 requires that any control relied upon to perform safety critical functions be evaluated as an SREC. Safety critical functions are those intended to reduce risk during normal and abnormal conditions, such as:

• Limiting power or cutting power when excessive temperatures are detected
• Preventing access to hazardous voltages during maintenance
• Maintaining user assessable outputs within non‑hazardous energy levels (i.e., Class 2 or LVLE)

If a product relies on electronics to perform these functions, Supplement SA directs the evaluation toward UL 60730-1, Annex H, which is the foundation for functional safety assessment.

Control Function Classes: Why Classification Matters

IEC/UL 60730-1 has three classes of control classification (A, B, C). LED driver and lighting protection functions will fall under Class B, making them subject to hardware, EMC, and sometimes firmware evaluation under Annex H.

• Class A: Controls not relied upon for risk mitigation; this only addresses inherent fire/shock hazards associated with a product (no functional safety evaluation required).

• Class B: Controls relied upon to mitigate fire hazards, shock hazards, or personal injury risks (functional safety evaluation required).

Note: Class C covers special hazards (i.e., risk of explosion) and will likely not be applicable to UL 8750.

Understanding the Safety Function

Functional safety starts with clearly defining the safety function. This includes understanding the full “safety-critical thread”:

• Input: the sensing element (e.g., temperature probe)
• Logic: processing circuitry (e.g., microcontroller with embedded firmware, analog comparison circuits and logic gates, programmable logic controller)
• Output: the actuator that removes or limits power (e.g., relay, drive IC, etc.)

For example, for an over-temperature protection function, a temperature sensor feeds data to a microcontroller I/O input, which then commands a relay or driver IC to de-energize the load, as necessary. Every element in this loop must be reviewed, including the safety-critical microcontroller pins.

Fault Tolerance and Single-Fault Conditions

For Class B controls, UL 60730-1 requires single‑fault tolerance. This means that under any single component fault, the system must either:

• Continue to perform the safety function as declared, or
• Transition to a safe or risk‑addressed state (may include product “bricking” or hard lockouts)

Continued operation with the loss of the safety function is never considered acceptable. Designs often achieve compliance through redundancy, fail-safes, or independent shutdown paths. Fault tolerance is not optional – it is a core design expectation to be considered during development and proven and documented via an FMEA analysis. 

The Role of an FMEA in SREC Evaluations

A Failure Mode and Effects Analysis (FMEA) is central to demonstrating fault tolerance. The FMEA examines:

• How each safety-critical component can fail (open, short, for IC’s – pins pulled high/low and short to adjacent pins, etc.)
• The effect of that failure on the system
• Whether the safety function remains intact or the system enters a safe state

UL 60730-1, Annex H provides a fault mode table that provides guidance as to component failures which must be considered, or which may be excluded. The results of the FMEA analysis are typically subject to laboratory fault testing by an NRTL as a spot-check of the FMEA. 

Hardware, EMC, and Software: What Gets Evaluated?

An SREC evaluation under Supplement SA may include:

• Hardware assessment: Fault tolerance, component reliability, environmental stress testing, and electronic fault testing.
• EMC immunity testing: Verifying safety functions before and after EMC disturbances, across different operating modes.
• Software/Firmware evaluation (if applicable): Demonstration of mitigation measures to avoid systematic (people, processes, tools) and random errors (microelectronic hardware and system faults).

In some cases, a firmware evaluation may be waived – such as when independent redundant hardware channel or a separate hardware/software channel can fully uphold the safety function. However, a functional safety evaluation is still required even for hardware‑only designs.  

Final Thoughts

Safety-related electronic circuits are no longer an edge case – they are a reality of modern lighting design. Understanding when and how UL 8750 Supplement SA applies allows development teams to address functional safety early, reduce redesign risk, and move through certification more efficiently.

By clearly defining safety functions, designing for fault tolerance, and aligning with UL 60730-1 Annex H expectations, manufacturers can confidently bring safer, more robust products to market.