MCBs

Protecting your electrical devices and systems against electrical over-current is crucial for ensuring safety and avoiding hazard such as an electrical fire. Miniature Circuit Breakers (MCBs) are a simple and highly effective way of shutting equipment down preventatively in the event of over-current. Here at Cromwell, we have a wide range of MCBs from leading brands such as ABB, Schneider Electric and MK Electric.

Why MCBs?

An MCB - Miniature Circuit Breaker - is designed with the specific purpose of interrupting or stopping current flow if necessary to prevent the risk of fire, electrical over-current caused by a short circuit or electrical overload. Unlike fuse wire which can only be used once and once blown in an overload cannot be revived, MCBs are usually not destroyed during electrical over-current and can therefore be used multiple times.

MCB types

There are six types of MCB (Miniature Circuit Breaker), however the most commonly used are types B, C and D. The different types of MCB differ in their trip curve. A trip curve simply refers to the maximum current that an MCB can withstand before being destroyed in an over-current, or the amount of current that the MCB will allow in a power surge. Below, we've outlined the six types of MCB to allow you to make a confident purchase and to better understand our range of MCBs.

• Type A   -    This type of miniature circuit breaker is designed to trip off the circuit when the current exceeds 2-3 times the actual current rating. In simple terms, this is a highly sensitive MCB that is likely to short circuit and is thus better suited for use in semiconductor devices such as a bipolar transistor.

• Type B   -    These type of MCBs trip off the circuit when the current exceeds 3-5 times the actual current rating and is most commonly used for cable protection and smaller residential applications on devices with mainly a resistive load.

• Type C   -   This type of miniature circuit breaker is designed to trip off the circuit at currents that reach 5-10 times their rated load. These are generally used for commercial, domestic and smaller industrial applications.

• Type D   -    This type of miniature circuit breaker is designed to trip off the circuit at currents that reach 10-20 times their rated load. These are generally used in heavy duty applications where strong surges of power can occur occasionally. Examples of where Type D MCBs are useful include X-ray machines, big motors or industrial welding equipment.

• Type K   -   Designed to withstand 8-12 the recommended maximum rated load, type K MCBs are generally used in motors.

• Type Z   -   Type Z MCBs are similar in function to type A miniature circuit breakers, with a maximum capacity of 2-3 times their maximum rated load. They are also most commonly used in semiconductor devices due to their sensitive nature.

FAQs

When to use an MCB or MCCB?

Similarly to MCBs (Miniature Circuit Breakers), MCCBs (Moulded Case Circuit Breakers) are a device used to trip circuits when there is a risk of fire or hazard due to a unsustainable power surge. However, MCBs are generally used in low circuit current applications in domestic settings, designed for low voltage circuits that possess fixed trip curves that aren't suitable for adjustment. MCCBs however, are suited for high energy requirement applications where a higher voltage is needed. MCCBs also have adjustable trip characteristics, making them useful in demanding, industrial applications.

Which is better an MCB or fuse?

Both MCBs and fuses serve a similar function; they are both designed to trip a circuit when there is an excess or dangerous current due to overload. However, fuses work by literally melting when under extreme heat to trip the circuit, meaning they can only withstand one circuitry overload before needing to be replaced. Conversely, MCBs do not require replacement after use as they break the circuit via their internal switch that gets tripped when there is an excess current.