DC Fuse
14 April 2016
Protection of Datalogger Systems Against Sudden Overvoltage
14 April 2016
Residual current devices (RCDs) are designed to protect the system by disconnecting the circuit in case of insulation faults in facilities. According to their purpose, RCDs are divided into two types: 30 mA for human protection and 300 mA for fire protection. The RCD continuously monitors the current flowing through the phase and neutral conductors. If the difference exceeds 30 mA or 300 mA, the device trips. Currents above 30 mA are harmful to the human body, which is why this value is chosen in standards. Currents exceeding 300 mA pose a fire risk due to overheating, so leakage currents above this value are not acceptable. These values are defined in IEC 60479-1.
Why Use Residual Current Devices?
Using a 300 mA RCD for fire protection at the main distribution points and a 30 mA RCD for life protection at secondary distribution points, along with thermal-magnetic circuit breakers or automatic fuses (separately or together), ensures selectivity between all protection devices. Guidelines for the correct use of RCDs are described in the Regulation on Electrical Installations and Grounding. According to Article 315 of the Occupational Health and Safety Regulation, RCDs prevent leakage currents from exceeding certain limits and act as a protective device in grounded systems if a grounding fault occurs.
Another common misconception is confusing RCDs with fuses. Fuses protect facilities from extreme damage such as fire by tripping according to their characteristic when excessive current flows. Therefore, fuses are never a primary protection device. RCDs, on the other hand, trip when a fault current occurs in the circuit, according to IEC/EN 61008 standards.
Relevant Standards
There are many national and international standards for residual current devices. Some of the main ones are:
- TS EN 61008-1,
- TS EN 61008-2-1,
- EN 61008-1,
- EN 61008-2-1,
- IEC 61008-1, IEC 61008-2-1
RCD Classes
AC class devices are used in general power circuits and lighting distribution systems.
A class devices are used in electronic applications such as induction furnaces, pumps, and machinery.
Si class devices are used in regions prone to lightning strikes, and in facilities using variable speed drives, frequency converters, or electronic ballasts.
SiE class has the same application as Si class but provides extra protection against moisture, humidity, and corrosion. It is preferred for ships and high-risk facilities.
