RCD Testing


RCD/ELCB/Safety Switches and ground fault detector circuit breakers are used in mains meter boxes and as portable devices to protect personnel against faulty household and industrial circuits as a result of equipment fault or failure. Mains mounted RCD's along with portable units found on extension leads and integrated with power boards can fail as a result of abuse, age, corrosion, ingress of water or dirt and welded contacts. These products need to be regularly tested for personal safety as well as compliance to the appropriate standards. Test periods vary depending on the location and current flowing, higher current result in the potential for the contact to “stick” and fail to open under fault conditions. An absolute minimum annual testing should be used. Quarterly testing is recommended as a more reliable strategy.

MeasureSafe is easy to use - just plug it into the power outlet connected to an RCD circuit and select the appropriate RCD type then press the test button. The unit will automatically test the RCD and report the mains voltage along with the current and time taken to trip on alternative tests. Alternatively service personnel with more advanced knowledge can set up their own test conditions.

RCD devices are built to a range of specifications depending on the installation application and will break the mains electrical circuit when an imbalance is detected between the active and neutral current supplied to the circuit (ie. there is a leakage current to earth). The current and time thresholds for tripping the RCD (which are designed into each RCD device) must operate before the leakage current poses a life threatening hazard to personnel operating attached equipment.

The typical threshold of a household RCD will trip at a current of 30 milliamperes and a time of less than 30 milliseconds. However RCD designs will vary from 10 to 50 milliamperes with trip times up to 300 milliseconds, depending on the application and intended use.

The MeasureSafe 36B can test all currently available RCD's by simulating various earth leakage problems. In addition the MeasureSafe 36B will also report the mains voltage and incorrect wiring of outlets. Suspect equipment can also be tested whilst in operation to provide earth leakage operating margins to identify nuisance tripping problems or faulty equipment. Simply connect the MeasureSafe 36B measure the trip current, then remove the suspect equipment redo the current trip test then the difference is the leakage current from the test equipment.

In order to properly test both the trip current and the trip time two separate tests must be performed. The trip time is measured when the RCD trip current is applied to the RCD, the time taken to trip is then measured. The trip current is measured by slowly incrementing the leakage current from 0 mA until the RCD trips, then the current at which the unit tripped is recorded. Both test results are displayed and recorded for later download using the M36 Reporter software, free download. The MeasureSafe 36B can record up to 4000 test results recording time date and test performed and results.

The MeasureSafe 36B has an I-Test and T-Test button this can be used to manually select a particular type of test, either current trip test (I-test) or time trip test (T-Test). If neither is selected then the unit will intelligently alternate between the two tests each time it powers up. This provides minimal operator setup for each test. Totally automatic testing is performed by simply plugging in to an RCD equipped outlet and when the ready screen is displayed the test button is pressed.

A selectable, "test slope" feature for testing the worst case response time, is available on the MeasureSafe 36B. This enables the RCD to be repeatability tested. Once selected this will become the default setting for future tests but can easily be reset. The selectable RCD type is used to test the trip time and current, of the different RCD type categories. There is also a "custom type" setting to enable the selection of a customised value.

The testing slope can be best described using the diagram below the red sine wave indicating the main voltage.

The MeasureSafe 36B can test with the load starting at each of the 4 major points as indicated above. Surprisingly enough differing results are obtained depending on the starting point of the power cycle.

RCD Testing


Using Isolation Transformer