Residual Current Device (RCD) Tests
Short answer: Residual current device (RCD) tests verify that the residual current protection device interrupts the circuit at the defined tripping current and duration. RCDs are one of the most effective protection devices against electric shock, and the test button alone is not sufficient.
RCDs (residual current devices) prevent fatal electric shock by interrupting the circuit within milliseconds in the event of a leakage or direct contact. A 30 mA RCD provides typical protection for human safety.
However, an RCD only protects if it is actually functioning correctly. A mechanically jammed relay or one that has lost its sensitivity over time may not trip in the event of a real leak. Therefore, simply pressing the test button is not enough; the actual tripping current and duration must be measured with the device.
What is done during an RCD test?
- Verification of the tripping current (e.g., 30 mA) with the device.
- Measuring the opening time and comparing it with the limit value.
- Test button and mechanical function check.
- RCD type (AC/A/B) suitability for the load
- Selectivity and circuit protection suitability
Why is the Test Button Insufficient?
The test (T) button on an RCD only indicates that the relay's mechanical tripping mechanism is active; it does not measure the actual protection performance. An RCD may trip when the button is pressed, but it may not trip at the defined leakage current (e.g., 30 mA) or for the required time. For accurate evaluation, a special test device is used to measure at what current and for how long the relay trips. The RCD type is also important: AC type only detects sinusoidal leakage, type A detects leakage with a pulsed DC component, and type B detects straight DC leakage from loads such as drives/inverters. Choosing the wrong type can lead to the leakage not being detected at all.
Legal Basis and Accurate Assessment
Leakage current protection is one of the fundamental tests in periodic inspections of electrical installations; the tripping current and duration are measured and documented in a TÜRKAK accredited report.
For a complete list of the inspection areas we are accredited in and official TÜRKAK scope verification: Our Accreditation Scope.
Frequently Asked Questions
Is the RCD test button sufficient?
No; the button only controls the mechanism, the actual tripping current and duration must be measured with the device.
What does a 30 mA RCD provide?
This is a typical safety feature; it prevents electric shock by quickly opening the circuit in case of leakage current.
Why is RCD type important?
An unsuitable type for the load (e.g., AC type in an inverter load) may not be able to detect some leakage.
Ensure your safety with accredited measurement.
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