Miniature circuit breakers

MCCB (moulded case circuit breaker) or MCB (miniature circuit breaker) and contactor] and the overload relay. These recommendations permit damage of components on fault to varying degrees as noted below ... 

Amongst the diverse uses in the electrical/electronics field are coil formers, miniature circuit breakers, picture-tube mountings, edge connectors and telephone distribution boxes. 

Always use appropriately rated circuit safety devices such as fuses and MCBs (miniature circuit breakers). Make sure they are placed correctly according to code. 

If you are interested in a hybrid storage system with a battery, you can use a blocking diode and you should definitely fuse the battery, or use MCBs (miniature circuit breakers) to prevent possible problems from a short. 

When an earth fault occurs at the far end of a cable it is possible that the armouring, cable gland and the frame of the consumer equipment can be raised to a dangerous potential with respect to electric shock exposure to human operators. This subject has been given considerable attention over the last 20 years, and is well documented in for example IEC60364. The international documentation concentrates on low voltage fixed and portable equipment protected by fuses and miniature circuit breakers. See also Chapter 13. 

The hand-reset feature of a moulded case or miniature circuit breaker may replace the 86 relay. There may be a project requirement to use fuses. For low power circuits an auto-reset device (29) may be acceptable, provided that it does not reclose the circuit breaker or contactor. 

To prevent people from receiving an electric shock accidentally, all circuits contain protective devices. All exposed metal is earthed fuses and miniature circuit-breakers (MCBs) are designed to trip under fault conditions, and residual current devices (RCDs) are designed to trip below the fatal level as described in Chapter 4. 

Fault protection - is provided by protective bonding and automatic disconnection of the supply (by a fuse or miniature circuit-breaker, MCB) in accordance with lET Regulations 411.3 to 6. 

MCBs to BS EN 60898. These are miniature circuit-breakers (MCBs) which may be used as an alternative to fuses for some installations. The British Standard includes ratings up to 100 A and maximum fault capacities of 9 kA. They are graded according to their instantaneous tripping currents - that is, the current at which they will trip within 100 ms. This is less than the time taken to blink an eye. 

The single-storage heater is heated by an electric element embedded in bricks and rated between 6 and 15kW depending upon its thermal capacity. A radiator of this capacity must be supplied on its own circuit, in cable capable of carrying the maximum current demand and protected by a fuse or miniature circuit-breaker (MCB) of 30, 45 or 60 A as appropriate. At the heater position, a DP switch must be installed to terminate the fixed heater wiring. The flexible cables used for the final connection to the heaters must be of the heat-resistant type. 

MCBs to BS EN 60898. These are miniature circuit breakers (MCBs) which may be used as an alternative to fuses for some installations. 

Some British Standard numbers are written as BS EN followed by a number. This means that the British Standard is in harmony or agreement with the European Standards. These standards apply to all countries in the EEC, for example BS EN 60898 1991 is the British and European Standard for miniature and moulded case circuit breakers which were issued in 1991. 

Electrical installations, whether temporary or permanent, together with electrical equipment and apparatus, should be protected by a range of measures including residual current devices (RCDs) which protect human beings from electrical shock, fuses and miniature moulded case circuit breakers (MCCBs) which provide protection to apparatus from overheating and short circuits. Arrangements should be in place to ensure that all electrical work to installations and/or electrical equipment is undertaken by only trained, qualified and competent electricians who are familiar with the systems involved. 

Protection Against Short-circuit Current. A short circuit is a special case of excess current. However, a short-circuit failure differs from overload in that damage to the circuit and cables occurs very rapidly. Protective devices must therefore be able to respond quickly to these failures. As far as any type of fuse is concerned a short-circuit failure will cause it to operate more rapidly because of the increased thermal effect. Circuit-breakers, on the other hand, usually have a separate part of their operating characteristic which is specifically designed for short-circuit failures. A miniature... 

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