Why are there so many RCD (Residual Current Device) specs and mA tripping thresholds for use in equipments in Europe vs the USA where they were not used (but only 5mA GFCI for personal safety)?
Don't they use any EGC (Equipment Grounding Conductor connected directly to the utility transformer) in Europe that requires such massive RCD specs?
Lastly. Is the RCD in Europe compatible when used in the USA 240v ac (red and black wire)? Has anyone successfully used RCD in the USA? In theory it should work because the toroid only detect imbalances but some people comment that they were not compatible for some reasons. True?
Best Answer
There are many different classes of RCD's and GFCI's. The 5mA 5 second test is the most common residential for bathroom grounded outlets or wherever secondary earth paths exist. ( see AC-2)
The selection criteria is based on location between source and load, country laws , and to avoid nuisance trips yet to prevent:
The typical HIPOT leakage test in America is < 100uA using HVDC to eliminate the AC filter earth current but where 500uA is allowed per unit which comes from the EMI ground noise PI filter current. Up to 2.5mA earth current is allowed per system that contains many PSU's.
Both RCD's and GFCI's measure the differences in line current to magnetically activate a relay. The construction depends on the current rating and residual difference threshold and thus the acceleration which affects the response time. Higher thresholds or time delays are selected to avoid nuisance trips such as from transient voltage suppressor currents to to earth.
Although a 5mA threshold device is more protective than 30 mA device, in residential areas with high humidity and dust, the device may false trip until the moisture or contaminants that cause the internal leakage to earth evaporate or are heated away.
Residential RCD's with 30mA threshold may be common but in America GFCI's now must have a 5mA/25ms threshold on outlets near moist connections to earth. Laundry room, unfinished concrete basement, outdoors, kitchen, bathroom. Old houses with 2 wire outlets may use these in place or rewiring the house with 3 wire if labelled as "no equip. ground".