GB/T 4943.1-2022 SELV Testing Requirements

With the implementation of GB/T 4943.1-2022 Audio, Video, Information Technology and Communication Technology Equipment – Part 1: Safety Requirements, the safety assessment of information technology, audio, video and communication products has entered a new stage focusing on hazard control.

During testing, we have found that technical issues related to Separated Extra-Low Voltage (SELV) remain one of the most common non-conformities for Class III equipment and low-voltage powered products.

The main reason is that the understanding of SELV is limited to the misconception that "low voltage equals safety", while ignoring the standard requirements for construction and fault conditions.

This article systematically explains the basic testing requirements for SELV in GB/T 4943.1-2022 from a practical testing perspective, and introduces several frequently performed test items.

Understanding SELV

In GB/T 4943.1-2022, SELV is not merely a voltage value, but a complete electric shock protection system.

When conducting SELV-related assessments, testing institutions generally judge from the following three aspects:

1. Whether the voltage and energy itself fall within the safe range;

2. Whether the SELV circuit is reliably isolated from hazardous voltage circuits;

3. Whether the safe state can be maintained under abnormal or single-fault conditions.

Only when all the above conditions are met can a circuit be identified as a standard-compliant SELV circuit.

Basic Test Item 1: SELV Output Voltage Verification

4. Test Purpose

This test confirms that all accessible SELV output ports of the equipment pose no electric shock hazard to personnel under normal operating conditions.

5. Key Testing Points

Measurements and verifications are performed under the following conditions:

• Normal operating state

• Rated load condition

• No-load or light-load condition

• Different operating modes (e.g. standby, operating switching state)

6. Judgement Principles

The output voltage shall always stay within the SELV range, with common limits as follows:

• AC voltage not exceeding 30 V

• DC voltage not exceeding 60 V

7. Testing Experience Tip

In practice, voltage rise under no-load or abnormal control conditions is a common problem. Therefore, manufacturers are advised to conduct sufficient multi-state self-tests before submission, rather than only testing under rated working conditions.

Basic Test Item 2: Isolation Assessment Between SELV and Hazardous Voltage

1. Test Purpose

This test verifies that adequate electrical isolation exists between SELV circuits and potentially hazardous voltage circuits, preventing hazardous voltage from reaching accessible parts.

2. Testing Content

Key focus areas include:

• Whether clearances and creepage distances meet standard requirements

• Structural integrity of solid insulating materials

• Whether PCB layout and routing weaken isolation

• Whether production processes affect the original isolation structure

3. Analysis of Common Issues

Some products meet requirements at the design stage, but actual isolation is weakened during later structural adjustments, material replacement or production, resulting in SELV protection failure. Such issues are particularly common in type testing.

Basic Test Item 3: SELV Verification Under Single-Fault Conditions

1. Test Purpose

GB/T 4943.1-2022 clearly specifies that safety design shall not rely on a single protective measure. Therefore, even if one component fails, the SELV circuit shall not turn into a hazardous voltage state.

2. Testing Method

Testing institutions typically simulate single-fault conditions artificially (e.g., component failure or functional abnormality), then re-evaluate the SELV output status.

3. Judgement Requirements

Under any single-fault condition:

• SELV output shall not exceed the safe voltage limit

• No new electric shock hazard shall be introduced

4. Testing Experience Tip

In some designs, SELV safety excessively depends on a single isolation component or control measure. Once the component fails, the low-voltage circuit may be directly exposed to hazardous voltage, which is one of the key concerns in testing.

Within the testing framework of GB/T 4943.1-2022, although Separated Extra-Low Voltage (SELV) is one of the most basic electric shock protection measures, its compliance directly determines the overall safety level and classification of the equipment.

SELV is not simply "low voltage", but a systematic safety requirement that requires multi-dimensional verification of voltage, structure and fault conditions.

Only with sufficient verification in design, production and testing can the safety requirements of GB/T 4943.1-2022 be fully satisfied.