What is the difference between short circuit values mentioned in the 2 standards , Icn values in IEC60898 & Icu value in IEC60947. There is also one observation that Icu values of MCB’s as per IEC60947 are higher than Icn values of MCB as per IEC60898.

No, your statement is not correct. MCB is a miniature circuit breaker and MCCB is a molded case circuit breaker. Difference is in the breaking technology and size. Where a more frequent switching is required, such as the switching on and off of banks of luminaires, the manufacturer’s instruction should be followed and preferably an alternative device should be selected. If I understood your question well, the difference comes from ratio of nominal Icn and ultimate Icu breaking capacities ratio to service breaking capacity Ics. It is usually stated in percentage 100%, 75%, 50% or less. As higher this value as more “robust” breaker to withstand Ics. Dear Sahad, it is normal having MCCB certified as per 947 in commercial/small commercial buildings with MCB’s certified as per 898. And it is wrong to use MCB’s dedicated for domestic applications (60898) in industrial applications installations. However if we perform the calculation using 230Vac will will get a reduced permissible Zs. This would seem to suggest to me that we could be failing Zs values that allow enough current to flow in the event of a fault to trip the fault protective device.Table B6 of the OSG and Table A4 of GN 3 contain maximum Z s values for circuit-breakers based on the cross-sectional area (csa) of the protective conductor and at an assumed conductor temperature of 10°C. Assemblies such as distribution boards are validated with specific circuit-breakers installed and these cbs are usually from the same manufacturer as the distribution board. Where cbs made by a different manufacturer are to be installed, verification will have to be undertaken by the manufacturer of the distribution board to BS EN 61439-2 or BS EN 61439-3. Fitting unverified devices will invalidate any verification and the warranty. BS EN 60898-1:2019 Electrical accessories. Circuit-breakers for overcurrent protection for household and similar installations Circuit-breakers for a.c. operation For example, the BS EN 60898-1 standard describes B, C and D operating curves with ratio to rated current. But the BS EN 60947-2 standard prescribes an instantaneous tripping release which may be provided with a plus or minus 20% tolerance and adjustable as illustrated in Fig. 1. For this reason, manufacturers provide additional curves K, Z and MA to the B, C and D curves. Where manufacturers’ values of Z s for MCBs are used, they will often recommend multiplying the measured value of Z s by a correction factor, to correct for ambient temperature. For example, Schneider, recommend using a factor of 0.8,

But I’m still confused in case of MCBs that have 2 condition of breaking capacity depend on which IEC that MCB comforting to RCD as a term used without any further additional information would revert to the most commonly used general purpose version when quoting tripping times.. Are AC MCB’s able to be used for DC applications? If so, What is it about the Ac rated MCB’s that makes this possible? I am being told by an inspector that we have to use 230Vac when performing permissible earth loop impedance calculations as per BS7671:2018 clause 411.4.4 Zs × Ia ≤ U0 × Cmin. Maximum Z s values for MCCBs to BS EN 60947-2 are not included in BS 7671. Therefore, manufacturers’ tables should be consulted for the rating of the MCCB to be used.Thanks for your reply. One more question regarding RCCB. The printed label on RCCB is either 6000A or 10000A. Understand that is making capacity and not Short Circuit capacity. What this 6000A or 10000A meaning. If my outgoing MCB is 10KA, them I should use a 10000A RCCB. Is this correct? As mentioned in the blog, MCB manufactured as per IEC 60898 to be used in residential buildings or similar applications. In industrial applications can be used breakers certified as per IEC 60947-2 or IEC 60947-2 and 60898 both. IEC 60947-2 governs circuit breakers (CBs) for industrial applications. They protect electrical power distribution of up to 1000 volts a.c. and 1500 volts d.c. with an entire spectrum of rated currents from 0,5 to 6300A. Utilities and manufacturing facilities often use air circuit breakers (ACBs), molded case circuit breakers (MCCBs), and miniature circuit breakers (MCBs)