How to Identify Circuit Breaker Type

One panel provides four types of appliance, which are all types of switches: miniature circuit breaker, residual current devices, arc fault devices and moulded-case breakers in the main position. People acquire these appliances calling them “breakers.” The present article shows how to deal with the appliances based on their labels, shapes and functions.

It is easy to identify a type of switchgear or electrical device by knowing what type of protection it offers. An MCB provides protection against overloads and occurs in cases of short-circuit. An RCCB ensures protection against the current leakages but does not protect against overloads. An RCBO is a device that offers both types of protection at the same times. An AFCI or GFCI protects against arc-faults or earth-faults along with providing protection against overcurrent. MCCB is a larger version of moulded case switchgear that is used for currents at industrial levels and ACB is an open frame switchgear that is used for service outlets in big installations.

The Families, by Function

What is being given away all the time is how the device detects the current. In case of a device with a testing button, it can sense the current that is being carried wrongly, while the device without a testing button detects the amount of current. The device that has both current ratings and the testing button does both things. Frame size is the other clue: an industrial device with an adjustable trip unit and a far higher interrupting rating, such as this 1000 to 1600 A three-pole MCCB, is identified by size before markings.

Reading the Markings

The type of device can be easily identified by simply looking at the front face since the four parameters that define it are rated current, trip curve, breaking capacity, and standard.

A device that has a marking C20 is a C-curve MCB with a capacity of 20 A. A device that shows 20A 30 mA can be an RCBO or RCCB with 20 A capacity and 30 mA level of leakage. The device marked 6000 or 6kA specifies the fault current it can break, which is the value needed in order to check if it can be used in a specific place.

The boundary between a miniature and a moulded-case device is also visible in the marking. A single-width DIN rail device is an MCB, and the specification of this single-pole MCB shows the markings that identify it.

B, C and D Curves: Reading the Letter

The letter contained on the MCB or RCBO signifies the level of magnetic trip factor as compared with the rated current.

• Type B trip: between 3-5 times the rated current, used for resistive loads, wiring, and circuits with very low inrush currents.
• Type C trip: between 5-10 times the rated current for most general purpose applications such as plugs and circuits with a small motor and mixed electronics loads.
• Type D trip: between 10-20 times the rating, used for inrush loads, including electrical transformers and big motors.
• Type K and Z: for somewhat unusual applications, mainly specific for low-voltage applications like motors or semiconductors.

Choosing between the types is determined by load, not the manufacturer brand. A compressor with type B trip might disengage every time the machine starts, while a type D trip on the lighting circuit allow the actual overload to last long and melt the wires. The device with the right curve and the right rating, such as this 10 kA device offered in B, C and D curves, is selected by reading both numbers together.

North American and European Naming

The names differ in the two parts of the world that lead to purchasing mistakes.

A 30 mA RCD in Europe is called GFCI in North America, but the trip value is not the same. A Class A GFCI in North America trips at 4-6 mA while RCDs in Europe work at the value of 30 mA, but they can also function at 10 mA and 300 mA. It means a device bought in one market cannot be used in another market.

In North America a 2 poles device is considered “double pole”, while in Europe it is called “two pole” or “bipolaire”, and a 1P+N device breaks the current to the neutral circuit but does not protect it. RCBO in Europe is GFCI breaker with overcurrent circuit in North America and North America version is single pole while in Europe version is mostly 1P+N.

The construction of a European-style residual current device, with the test circuit and the 2-pole switching arrangement, is shown in this two-pole type B RCCB. Type B is important for one reason: it allows smooth residual DC current to be identified, something that Type A and Type AC products can’t do, something that is crucial for modern inverter drives and some electric vehicle charging stations.

The Three Types of Breaker People Mean

When one asserts that there exist three types of circuit breaker, they inevitably mean one of the two classifications, and both are accurate.

By construction, they are the miniature circuit breaker (MCB), the moulded-case circuit breaker (MCCB), and the air circuit breaker (ACB). This classification is an industrial one, which is based on frame size and interruption capability.

By trip curve, it is the type B, type C, and type D. This classification is a residential one, as it is based on the device’s reaction to inrush.

A fourth classification appears in relation to insulation medium at medium and high-voltage; this is air, vacuum, SF6, and solid-dielectric. This is the field of switchgear, and vocabulary here is entirely different.

Identifying a Device With No Markings

Old devices suffer from a loss of their printing. There are three ways to identify them. The first method is via a label on the panel that gives the name of the series it belongs to. The second method is physical size and the formation of the clips. This is unique to the manufacturer. The last method is to get information from the datasheet.Our technical download library holds dimension drawings for the KNB and KNL ranges, and a photograph of the device beside a rule is usually enough to identify a series.

What you should not do is replace by fragment. An item from a different series that fits your device will be incompatible with it. In this way, it will be hurting itself by overheating and failing to meet required specifications. This failure can turn $10 into the cost of a complete panel substitution.

FAQ

What are type B, type C, and type D circuit breakers?

They talk about trip curves rather than families. Class B breakers trip magnetically between three and five times rated load current; type C does that for 5 to 10 times; type D does so for 10 to 20 times. One chooses a corresponding curve based on inrush characteristics of the load.

How to identify circuit breakers without labels?

First, check it by the type of the panel, its dimensions, type of clip and datasheet of the manufacturer. Most appropriately, take a picture of the breaker and the rule, additionally remember from which manufacturer the panel is.

What are the three types of circuit breakers?

Based on their frame type: MCB, MCCB and ACB. Based on the type of the trip curves: B, C, D. In most cases these terms are interchangeable and you will be able to understand the system from the context.

How to know what type of circuit breaker to use?

You need to know the current rating of the equipment to be connected, inrush current of the machine, fault current and the panel type. The type of trip curve corresponds to the type of the load, while the rating to the cross-sectional area of the cable.

References

• NEMA — Circuit Breaker Types and Application
• UL Solutions — Overcurrent and Ground Fault Protection Devices
• Siemens — MCB, RCD and RCBO Selection
• ABB — Residual Current Devices and Type B Detection
• Rockwell Automation — Industrial Circuit Protection

Conclusion

The classification process depends on using the information gathered regarding the sensing capabilities of the device like ampere rating, curve, and ka ratings. It takes less than a minute to carry out classification as it only uses four screens and a key for testing purposes. It is a good idea to take a picture showing the front of the device along with its name plate so as to get verified about the family, series, and curve.