Residual Voltage in Luminaires: Why Is It Important and How Is It Tested According to IEC 60598-1?

1. What Is Residual Voltage in Lighting Products?
Have you ever wondered why an electrical device may still carry an electrical charge even after it has been switched off or disconnected from the power supply?

This phenomenon is known as residual voltage.

In lighting products, especially LED luminaires and portable lamps, electronic components such as capacitors are commonly used in LED drivers, power supplies, and compensation circuits.

These capacitors store electrical energy during normal operation. When the luminaire is disconnected from the power supply, the stored energy may not disappear immediately.

As a result, a voltage may remain between the power supply terminals, accessible connector contacts, or other relevant electrical points.

If the residual voltage remains too high, it may present an electric shock hazard to users who touch the plug pins or accessible electrical contacts shortly after disconnection.

This is why residual voltage testing is an important part of electrical safety verification for lighting products.

2. Why Do Luminaires Need Residual Voltage Protection?
To understand the importance of residual voltage protection, we first need to understand how capacitors work.

A capacitor stores electrical energy when connected to a power source. Even after the power supply is interrupted, the capacitor can retain part of its stored charge.

The larger the capacitance and the higher the operating voltage, the more energy the capacitor may store.

In a lighting product, the capacitor may discharge through internal resistors or other circuit components. However, if the discharge circuit is missing, improperly designed, or insufficiently effective, the voltage may remain above the permitted safety limit for too long.

This creates several potential risks:
- Electric shock when users touch accessible plug pins.
- Safety hazards during maintenance or replacement.
- Potential risks when handling portable luminaires immediately after disconnection.
- Non-compliance with applicable electrical safety standards.
Therefore, manufacturers need to verify that the discharge arrangement can reduce the residual voltage to the required level within the specified time.

3. What Does IEC 60598-1 Clause 8.2.7 Require?
The international standard IEC 60598-1 specifies general safety requirements and testing methods for luminaires.

Under IEC 60598-1:2020, Clause 8.2.7 addresses residual voltage requirements for luminaires incorporating capacitors.

The requirements distinguish between different types of luminaires and electrical connection arrangements.

The main requirements include:

These requirements are intended to ensure that residual voltage decreases to a safe level within the specified discharge period.

A few important points should also be considered:
- The applicable requirement depends on the luminaire category and connection method.
- Residual voltage is measured at the relevant electrical terminals or contacts specified by the standard.
- Where measuring compensation capacitors, the lamp may need to remain in the circuit if this produces a more onerous result.
- Measurements are performed on individual luminaires, even when they are installed in a multi-luminaire system.
Important: The above table summarizes IEC 60598-1:2020 Clause 8.2.7. Laboratories should verify the applicable requirements against the exact edition and amendments adopted for their certification or compliance project. IEC 60598-1:2024 is the tenth edition and replaces the 2020 edition. 

4. How Is Residual Voltage Testing Performed?

Residual voltage testing evaluates how effectively a luminaire's internal discharge circuit reduces stored electrical voltage after the power supply is disconnected.

A typical testing procedure involves the following steps:

Step 1: Prepare the test specimen

Connect the luminaire to the test equipment according to the applicable test circuit and ensure that the required electrical connections are correctly established.

Step 2: Apply the specified power supply

Energize the specimen at the required supply voltage and operating conditions. The test should follow the applicable standard's requirements, including the specified disconnection condition.

Step 3: Interrupt the power supply

Disconnect the power supply at the required point in the AC voltage cycle. The product's residual voltage tester supports power interruption at peak supply voltage to provide repeatable test conditions.

Step 4: Measure the residual voltage

Measure the voltage remaining between the relevant electrical points, such as:

• Between power supply terminals.

• Between power supply terminals and the equipment enclosure.

• Across externally accessible capacitors, where applicable.

Step 5: Evaluate the measurement results

Compare the measured voltage with the applicable voltage limit and discharge time.

For example, for the relevant portable luminaire category, the voltage between plug pins or accessible connector contacts must not exceed 34 V one second after disconnection under the 2020 edition requirements.

Step 6: Record the test results

Record the measured residual voltage, test conditions, and compliance evaluation for laboratory reporting.

The exact test sequence and measurement connections should always follow the applicable standard and test specimen configuration.

Product details: IEC 60598-1 Clause 8.2.7 Portable Luminaire Residual Voltage Tester – SN-SY2000W