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Circuit Breaker FAQs


In order to flow, current electricity requires a circuit - a closed, never-ending loop of conductive material. Current is the rate at which electrons flow past a point in a complete electrical circuit. At its most basic, current = flow.

Current is measured in amperes (AM-pir), or amps. It expresses the quantity of electrons (called "electrical charge") flowing past a point in a circuit over a given time.

A current of 1 ampere means that 1 coulomb of electrons—that's 6.24 billion billion (6.24 x 1018) electrons—is moving past a single point in a circuit in 1 second. The calculation is similar to measuring water flow: how many gallons pass a single point in a pipe in 1 minute (gallons per minute, or GPM).

Symbols used for amps:

  • A = amperes, for a large amount of current (1.000)
  • mA = milliamperes, a thousandth of an amp (0.001)
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Alternating current (AC) frequency is the number of cycles per second in an AC sine wave. Frequency is the rate at which current changes direction per second. It is measured in hertz (Hz), an international unit of measure where 1 hertz is equal to 1 cycle per second.

  • Hertz (Hz) = One hertz is equal to one cycle per second.
  • Cycle = One complete wave of alternating current or voltage.
  • Alternation = One half of a cycle.
  • Period = The time required to produce one complete cycle of a waveform.

At its most basic, frequency is how often something repeats. In the case of electrical current, frequency is the number of times a sine wave repeats, or completes, a positive-to-negative cycle.

The more cycles that occur per second, the higher the frequency.

Example: If an alternating current is said to have a frequency of 3 Hz (see diagram below), that indicates its waveform repeats 3 times in 1 second.

Frequency is typically used to describe electrical equipment operation. Below are some common frequency ranges:

  • Power line frequency (normally 50 Hz or 60 Hz).
  • Variable-frequency drives, which normally use a 1-20 kilohertz (kHz) carrier frequency.

Equipment designed to operate at a fixed frequency performs abnormally if operated at a different frequency than specified. For example, an AC motor designed to operate at 60 Hz will run slower if the frequency drops below 60 Hz. It will run faster if it exceeds 60 Hz.

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Direct current is a bit easier to understand than alternating current. Rather than oscillating back and forth, DC provides a constant voltage or current. DC is defined as the "unidirectional" flow of current; current only flows in one direction.

Using our water analogy again, DC is similar to a tank of water with a hose at the end. The tank (i.e. the battery) provides storage. It can only push water one way - out the pipe. Similar to a DC-producing battery, once the tank is empty, water no longer flows through the pipes.

Direct current (DC) can be generated in a number of ways:

  • Batteries provide DC, which is generated from a chemical reaction inside the battery
  • An AC generator equipped with a device called a "commutator" can produce direct current
  • A device called a "rectifier" converts AC to DC



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Alternating current describes the flow of charge that changes direction periodically. As a result, the voltage level also reverses along with the current.

Home and office electrical outlets are almost always AC. This is because generating and transporting AC across long distances is relatively easy. At high voltages (over 110kV), less energy is lost in electrical power transmission. Higher voltages mean lower currents, and lower currents mean less heat generated in the power line due to resistance. AC can be converted to and from high voltages easily using transformers.

AC also powers electric motors. Motors convert electrical energy into mechanical energy. When the motor shaft is spun, a voltage is generated at the terminals! Many large appliances like televisions, dishwashers and refrigerators have their own AC motors.

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Circuit Breaker Basics

A circuit breaker works like a fuse to protect equipment, but it has important differences

  • A circuit breaker may be reset after interrupting an overcurrent event as a result of an overload, short circuit, arc or ground fault.
  • Has a higher initial cost, but does not need replacing after an overcurrent event.
  • Often has additional protective features like an alarm or auxiliary switch.
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Although circuit breakers come in many designs, the main components are universal.

  1. Frame – provides the rigidity and strength to protect internal parts and provide insulation.
  2. Handle or toggle – opens and closes the circuit breaker. For bigger circuit breakers, a 2-step process protects and assists the operator.
  3. Contacts – when contacts connect, they allow the current to flow. Contacts for low-voltage breakers are found in the arc interruption chamber.
  4. Arc extinguisher – Extinguishes an arc when the circuit breaker interrupts a fault. Arcs cannot be prevented so circuit breakers are designed to control them
  5. Trip unit – Opens the operating mechanism if there is a prolonged overload or short circuit. Trip units can be electro-mechanical or electronic.


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A short circuit is an overcurrent which greatly exceeds the normal full load current of the circuit. A short circuit leaves the normal current carrying path of the circuit and takes a short-cut around the load and back to the power source. A short circuit is an overcurrent but not an overload.

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Rocker mounted circuit breakers have a special rocker guard that makes it possible to lock the handle in the on or off position. Our front-mounted circuit breakers have different handles for managing unintentional tripping.

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An overcurrent condition happens when the electrical current exceeds the rated (or expected) current of equipment or the ampacity of a conductor. If an overcurrent is allowed to continue, it could result in a fire, conductor insulation damage and equipment damage. Overcurrent is the result of an overload, short circuit, arc or ground fault. 

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An overload condition happens when equipment operates in excess of normal, full-load rating. ,If left to persist for a sufficient length of time, it would cause damage or dangerous overheating. An overload is NOT a short circuit, ground or arc fault.

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Yes and no, mostly due to the technology of the circuit breaker employed.  For hydraulic magnetic technology refer to the diagram below.  The effect of gravity on the tripping mechanism is due, or not, to the gravity forces being influential on the mechanism.  For example, aiding the tripping will be faster and opposing tripping will be slower.

Circuit breakers using alternative technologies, thermal-magnetic and electronic magnetic, are not likely to be affected in a similar fashion.

The technology employed is not usually indicated on the body of the circuit breaker so that at any time there is the consideration to mount the circuit breaker away from the industry norm of vertical the manufacturer should be contacted to confirm if the proposed mounting has any effect.


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All units get hot under 100% rated current.  Operating temperatures can be affect by ambient temperatures, and by the cable size.

CBi breakers are expected to operate at 40° Celsius. Thermal Breakers de-rate after 40° Celsius, but CBi hydraulic-magnetic circuit breakers do not de-rate until 85° Celsius.


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Yes, as the mechanism is temperature-independent, high or low ambient temperature is not a factor. But, for example at -40 degrees the action of the breaker will be somewhat more sluggish and at +85 degrees it will be more rapid. But it will always keep to the stated rated current.

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When choosing the circuit breaker type, consider the overall voltage rating of the electrical system. This rating is calculated by the highest voltage that can be applied across all end ports. Also, the voltage distribution and circuit breaker integration apply during voltage calculation.The circuit breaker should have enough voltage capacity to meet the requirements of the end application.

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The operating current or amperage is a factor to consider when choosing a circuit breaker. The circuit breaker should operate at 100% of the required load. However, you are advised to choose a circuit breaker approximately 120% of the required load.A higher amperage helps off set the effects of heat generation in the power system. The amperage rating is the continuous current carried in the ambient temperature. Circuit breakers should be calibrated to a standard 104°F. (All the source of information about the load cycle is obtained from the National Electrical Code.)

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To choose a circuit breaker, you need to determine which trip curve is the correct one for your application. A trip curve, also known as a time current curve, is a graphical representation of the expected behavior of a circuit protection device.

Trip curves plot the interrupting time of overcurrent devices based on a given current level. They are provided by the manufacturers of circuit protection devices to assist users with selecting devices that provide proper equipment protection and performance, while avoiding nuisance tripping.

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The maximum amount that the current breaker can interrupt is the interrupting rating. It is crucial to determine the maximum interrupting rating of the power system. When buying a circuit breaker, the interrupting capacity must be equal or greater or equal than the fault current.

An interrupting capacity less than the amount of fault current can damage the circuit breaker. This rule must always apply when purchasing any circuit breaker.

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Some working conditions are very unforgiving for circuit breakers.

Ambient Temperature

An ambient temperature higher than 104°F requires calibration. High ambient temperatures can alter the performance of the circuit breaker. Since most enclosures are about 104°F, this is the standard calibration for almost all indoor circuit breakers. Anything lower or higher than 104°F might require you to upward or downward calibrate.


Different circuit breakers fit different altitudes. For instance, in high altitudes above 6000 feet, the air is thinner and does not conduct heat away from the current-carrying components. This means that the circuit breaker has to be calibrated for voltage, carrying ability, and interrupting capacity.

Thinner air prevents the build-up of dielectric charge that is capable of withstanding the voltage levels. Also, altitude can de-rate the power generation equipment. Talk to a power generation expert before purchasing circuit breakers for high attitudes

Moisture and Corrosion

For humid conditions, there is a recommend moisture treatment to help resist fungus and mould - notorious for destroying systems. In environments with high humidity, space heaters are often used in the enclosures.

Corrosion affects the components of the circuit breakers and thus leading to faulty systems. If they have to be used in corrosive areas, specially manufactured ones that are corrosion resistant should be used.

High Shock Probability

Some workplaces tend to have high probabilities of electrical shocks. In this case, anti-shock devices should be installed to prevent any mishaps.

Anti-shock devices consist of inertia counterweights over the poles that hold the trip bar. This weight, however, should not interrupt the functionality of the thermal or magnetic trip units.

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