Abstract
The use of residual current devices (RCDs) is obligatory in many types of low-voltage circuits. They are devices that ensure protection against electric shock in the case of indirect contact and may ensure additional protection in the case of direct contact. For the latter purpose of protection, only RCDs of a rated residual operating current not exceeding 30 mA are suitable. Unfortunately, modem current-using equipment supplied via electronic converters with a pulse width modulation produces earth fault currents composed of high-frequency components. Frequency of these components may have even several dozen kHz. Such components negatively influence the RCDs’ tripping level and, hence, protection against electric shock may be ineffective. This paper presents the results of the RCDs’ tripping test for frequencies up to 50 kHz. The results of the test have shown that many RCDs offered on the market are not able to trip for such frequencies. Such behavior was also noted for F-type and B-type RCDs which are recommended for the circuits of high-frequency components. Results of the test have been related to the requirements of the standards concerning RCDs operation. The conclusion is that these requirements are not sufficient nowadays and should be modified. Proposals for their modification are presented.
Highlights
Effective protection against electric shock in modern low-voltage electrical installations depends a lot on the proper selection, application, and operation of residual current devices (RCDs)
Research conducted by the authors and its results presented in this paper show that there is a strong effect of frequency on the tripping threshold of RCDs
Unfavorable behavior was noted for F-type and B-type RCDs, which are dedicated to circuits having earth fault current with harmonics
Summary
Analysis of provisions of the standard HD 60364-4-41 [1] shows that the highlysensitivity RCDs (rated residual operating current not exceeding 30 mA) are obligatory in socket-outlets circuits up to 32 A intended for general use, mobile equipment circuits up to 32 A for using in outdoors, and lighting circuits in premises designed to accommodate a single household. Even wide application of RCDs is required in special installations and locations mentioned in the 700 series of the standard HD (IEC) 60364 “Low-voltage electrical installations”. Such widespread use of RCDs as well as utilization of electronic equipment producing various shapes of earth fault currents prompt scientists and engineers from many countries to focus on the operation of RCDs under waveforms different than sinusoidal of the 50/60 Hz
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