Circuit Breaker Basics

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.

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.

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.)

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.

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.

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.

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.

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.

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.

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.

Altitude

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.

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.

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. 

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.