80% from site during test and inspection, the other 20% are from Engineers who are preparing / planning a job. Having a basic understanding of the RCD tripping parameters defined in the product standards, for different types of residual currents, can save time on site when testing unfamiliar devices. We have summarised the tripping characteristics for the various types of RCD detailed in 531.3.3 (see table further on). This can be used as a quick guide, for specific information for design purposes refer to the relevant product standard. For example, a Type A RCCB (EN61008-1) when subjected to an AC sinusoidal residual current is designed to trip at >50%35% We have come across examples of RCD Test Instruments that appear to have incorrect values programmed into the software. One example recently, testing on 30mA Type A setting ½ Pulse, recorded as fail – tripping at 12 mA i.e. 40%. The customer was not aware of the difference in the trip values, for AC and pulsating DC residual currents. He assumed the problem was associated with the RCD, not the software in the test instrument. If in doubt check with the Instrument Manufacture for software updates or your Trade Associat...