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Guide to Circuit Breakers

Circuit breakers are electrical safety devices designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of starting a fire. When choosing a circuit breaker to use for a particular system, there are several key things to consider. In this article, we will be discussing these major factors which include circuit breaker sizes, protection ratings, current types, and trip characteristics.

Though many variations exist, the most common types of circuit breakers typically fall under two categories: MCCB (Molded Case Circuit Breaker) and MCB (Miniature Case Circuit Breaker). The main difference between the two breakers is that a MCCB will be suited for higher energy environments, while mini-breakers are meant for smaller environments with lower current ratings. MCCBs are rated for current up to 1000-2500 Amps and their trip current may be adjustable. In addition, they have thermal-magnetic operation and an interruption current rating of up to 200,00 Amps. Conversely, MCBs have a rated current of no more than 100 Amps and have a trip current that is not adjustable. They also have thermal or thermal-magnetic operation and an interruption current rating of up to 18,000 Amps.

Circuit breakers will also have a protection rating which can generally be split into two types: UL489, and UL1077. UL489 rated circuit breakers provide overload protection to devices rated up to 600V and 600A, as well as short circuit protection, switching functionality, and disconnection function. Most UL489 devices are used in electrical distribution panels, so the minimum current ratings available are almost always greater than 15A. Alternatively, UL1077 rated circuit breakers are those that have been approved for use as overcurrent, over-voltage, or under-voltage protection within an appliance or other electrical equipment where branch circuit overcurrent protection is already provided or is not required. In essence, whereas other current breakers can be used on their own, UL1077 rated devices are supplementary protectors that are added on to an existing circuit breaker to extend its overload protection.

Another factor to consider when buying a circuit breaker is whether it is suited for AC or DC. If the current types of the two devices do not match up, the breaker will be ineffective at stopping the circuit. Trip characteristics are also important, and these are the thresholds in which the breaker will trip and will need to be reset. Generally, the higher the current spike, the faster the breaker will trip. For example, B-Trip protectors can trip between 3 to 5 times when receiving a full load current. They are commonly used in domestic systems and light commercial applications where surges are low. On the other hand, C-Trip protectors trip between 5 to 10 times when receiving a full load current. They are most suitable for commercial and industrial use where there are motors and a high number of fluorescent fittings which, when switched off together, may cause a high inrush current. Finally, Type-D trip protectors trip between 10 to 20 times when receiving a full load current. They are used more for specialist industrial use where current inrush can be high, such as in x-ray machines, pumping motors, and transformers.

Overall, circuit breakers come with many options for varying characteristics that can determine their suitability for use in different applications. You may want to consider sizing, AC/DC use, trip protection, and more when choosing a circuit breaker for your project. For additional help, on Industrial Part Numbers, we are ready to answer any questions, along with providing you access to a wide range of circuit breakers and other electrical equipment. Browse our online catalog of available parts or search for specific parts on our website using our optimized search tools. If any items pique your interest, you may simply submit an RFQ form as provided on our website to receive a custom quote for your comparisons in 15 minutes or less! Get started with Industrial Part Numbers today to experience a procurement process that is guaranteed to fulfill all your operational requirements with ease.


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