Selecting the Right Residual Current Circuit Breaker01.11.2021
RCCBs play a vital role in any protection system. RCCB is an amperometric protection device which is tripped when the system leaks a significant current to earth. This is paramount as it protects people from shock as well as your equipment from fires due to subsequent insulation failure.
This device continuously calculates the vector sum of the single-phase or three-phase system line currents and while the sum is equal to zero allows electricity to be supplied. This supply is rapidly interrupted if the sum exceeds a value preset according to the sensitivity of the device. RCCBs are only sensitive to current leakage to earth. They must be used in series with an MCB or fuse which protects them from the potentially damaging thermal and dynamic stresses of any over currents.
These devices are used in systems already equipped with MCBs which preferably limit the specific energy passing through, also acting as the main disconnecting switches upstream of any derived MCBs (e.g.: domestic consumer unit).
RCCB’s can be classed according to four parameters:
- type of construction
- detectable wave form
- tripping sensitivity
- tripping time.
According to the wave form of the earth leakage currents they are sensitive to, the RCCB’s may be classed as:
- AC type (for alternating current only)
- A type (for alternating and/or pulsating current with DC components)
- B type (for alternating and/or pulsating current with DC components and continuous fault current).
AC type RCCBs are suitable for all systems where users have sinusoidal earth current.
They are not sensitive to impulsive leakage currents up to a peak of 250 A (8/20 wave form) such as those which may occur due to overlapping voltage impulses on the mains (e.g.: insertion of fluorescent bulbs, X-ray equipment, data processing systems and SCR controls).
A type RCCBs are not sensitive to impulsive currents up to a peak of 250 A (8/20 wave form). They are particularly suitable for protecting systems in which the user equipment has electronic devices for rectifying the current or phase cutting adjustment of a physical quantity (speed temperature, light intensity, etc.) supplied directly by the mains without the insertion of transformers and insulated in class I (class II is, by definition, free of faults to earth). These devices may generate a pulsating fault current with DC components which the A type RCCB can recognize.
B type RCCBs are recommended for use with drives and inverters for supplying motors for pumps, lifts, textile machines, machine tools, etc., since they recognize a continuous fault current with a low level ripple.
Residual current sensitivity and environment
Household and special environments I_n_30 mA
High-sensitivity or physiologically sensitive RCCBs IEC/EN 60364 makes the use of these devices mandatory in all bathrooms, showers and private and public swimming pools and environments in which plugs and sockets may be installed without insulating or low safety voltage transformers
Laboratories, service industry and small industry I_n from 30 mA to 500 mA
Large service industry and industrial complex I_n from 500 mA to 1000 mA