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Circuit breakers, we’ve all seen one. Whether the application is in your home or an industrial factory, breakers have become the standard. Until now you may have never had to learn more about them besides what to do when one is tripped, altech_3but let’s take a look at some of the details of a circuit breaker and how that will guide your purchase.

Starting with the basics, we know a circuit breaker is a device that will interrupt the flow of current in an electrical circuit. This interruption protects the surrounding electrical components and wiring from damage caused by either electrical overloads or short circuits. Great, now that we know that; let’s explore the next step in figuring out what kind of circuit breaker you’re looking for.

Here at Marshall Wolf Automation, our most common types of circuit breakers fall under two categories: MCCB (Molded Case Circuit Breaker) and MCB (Miniature Case Circuit Breaker). The easiest way of discerning the two breakers is to remember a MCCB will be suited for higher energy environments, like commercial factories, while the mini-breakers are meant for smaller environments with lower current ratings.

MCCB Circuit Breaker:

  • Rated current up to 1000-2,500 Amps (depending on series and brand)
  • Trip current may be adjustable2POLEUL489
  • Thermal or thermal-magnetic operation
  • Interruption current rating of up to 200,00 Amps (Depending on series and brand)
  • – See all of Marshall Wolf’s MCCB Circuit Breakers here!

MCB Circuit Breaker:

  • Rated current of no more than 100 Amps
  • Trip current is usually not adjustable
  • Thermal or thermal-magnetic operation
  • Interruption current rating of up to 18,000 Amps (Depending on series and brand)

Now that we’ve determined the sizing of your circuit breaker we should move on to protection ratings. Commonly circuit breakers will have one of these protection ratings listed: UL489, UL508, and UL1077.

UL489: Considered to be the standard according to the National Electrical Code, UL489 Listed circuit breakers are considered “any listed circuit breaker that has an interrupting rating other than 5,000 Amps.” Overload tests are performed at six times the current rating of the device or 150A minimum. Devices rated up to 600V and 6,000A are covered in this standard. Beyond overload protection the UL489 rated circuit breaker must offer short circuit protection, switching functionality as well as disconnection function. Lastly, most UL489 devices are used in electrical distribution panels; therefore, the minimum current ratings available are seldom less
than 15A. –  See all of Marshall Wolf’s UL489 Circuit Breakers here!

UL508: The relevant standard for the control panel (factory wiring), covers control panels with a voltage up to 600 V for normal ambient conditions. “It applies between the electrical infeed and the outgoing feeder terminals to the field. On the topic of field wiring, only the interfaces (e.g. outgoing feeder terminals) to the field are dealt with.” Unlike the UL489 rating which generally includes overload protection and switching functionality, the UL508 also includes a disconnect function in most models when the application allows for disconnect means. – See all of Marshall Wolf’s UL508 Circuit Breakers here!

2000px-UL_Mark.svgUL1077: “The rating used for supplementary protection devices intended 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 layman’s terms, extra protection added on. Most UL 1077 circuit breakers are rated up to 63A/480Y/277V AC while the primary standard for UL1077 is the “fit-for-further-use” after a trip protection rating. – See all of Marshall Wolf’s UL1077 Circuit Breakers here!

Briefly I’d like touch upon the differences between AC and DC circuit breakers and the optional number of poles in your selected breaker. Seeing as Marshall Wolf primarily receives requests for AC circuit breakers I’ll use them as the standard in this blog; but it is important to mention that this is a detail you won’t want to skip. We know a circuit breaker’s primary function is to detect and trip when too much current (amps) is flowing through the circuit in order to protect the wiring from overheating.  During the act of disconnecting, the internal contacts separate and an arc is formed as the current jumps across the air gap.  (You have seen this happen on a smaller scale with a static electric shock.)  If this arc continues to jump the air gap, the current will continue to flow through the circuit, defeating the purpose of the breaker.  This arc must be extinguished.  The AC and DC breakers extinguish this arc differently making AC and DC breakers not interchangeable.

Pole options are pretty self-explanatory; your application will determine how many poles you’ll need on your breaker. Marshall Wolf Automation is a certified distributor of circuit breakers ranging from 1-pole to 4-poles depending on brand and series.

Marshall Wolf Automation carries breakers using Trip Characteristics; B, C, and D curves. For the sake of this blog I will only be covering these three trip-curve options due to their popularity but it is worth mentioning circuit breakers can also include Z or K curves.  The easiest way to describe trip characteristics is to think of them as the thresholds in which the breaker will trip and will need to reset. Generally, the higher the current spike, the faster the breaker will trip.

MCB-Types-type-b-type-c-type-d-1024x384Lastly, I would like to bring up accessories. Similar to contactors, our circuit breakers come with an array of accessory options based on your application needs. Depending on if you’re installing multiple breakers and are in need of busbars or have an emergency back-up system requiring a shunt our tech support can assist in finding the right accessory to further improve your circuit breaker’s efficiency and life span.

Now that we have a better idea of what to look for in circuit breaker, visit Marshall Wolf’s selection of UL Certified circuit breakers or if you have questions feel free to contact us today on our website at or email us at or call us at 847-658-8130.

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