Blog > Automation > Breaking Down Circuit Breakers
3/17/20 | Scott DeVost, Rexel Technical Consultant
Why are there so many different types of circuit breakers? How do I know which one I should be using? Do I need something from Allen-Bradley® Bulletin 140G from Rockwell Automation®, or would 1489-M be the better choice?
Let’s start with the main service entrance, feeder, or branch circuit protection. This would be a UL 489 product designed to protect the wire in the circuit. It is typically called a molded case circuit breaker (MCCB), and it will provide a disconnect means, as well as circuit protection. These products are generally large and have requirements for the distance between conductors and over air spacing. They are rated at no more than 80% of the continuous current unless marked for 100%.
Another type of circuit breaker is a supplementary protector. A supplementary protector is a UL 1077 device designed to protect the load it’s connected to. The supplementary protector needs to have an upstream device such as a molded case circuit breaker. Supplementary protectors can be applied at 100% of the rated current.
Garbage disposals are a residential example of a supplemental protector. If the disposal has a jam or too much in it, it will stop working. The unit is protected by a supplemental protector that protects the load by tripping. Once you clear the jam and the unit is allowed to cool, you can press the reset button on the disposal and use it again. The supplemental protector protects the disposal, while the breaker panel in the house protects the wire. Another benefit is that the circuit breaker in the panel doesn’t trip taking out the entire circuit, saving the walk to the breaker panel as well as keeping other devices on that circuit working.
Another type of circuit breaker is a breaker that is designed to protect a motor load. Motor protection circuit breakers (MPCB) are UL 508 devices and provide short circuit and overload protection for motor loads. Unless they are labeled a Type E self-protected device, MPCBs have the same spacing requirements as supplemental protectors. If they are a self-protected device, they will have the same spacing requirements as a UL 489 device and won’t need additional upstream protection. When paired with a contactor, they are sometimes referred to as a two-component starter. There is also a three-component starter that has a separate short circuit breaker, a contactor, and an overload device.
In summary, there are different breakers for different loads and applications. When applied correctly, they protect the wires in the circuit, as well as the loads that they are connected to. Circuit breakers can also help to isolate the problem to a local area before it becomes a widespread problem. If you need guidance on which breaker will work best for your needs, contact us today.
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