In this article, we will discuss the types of switches in the electrical industry. Stay with us to explore this important topic together.
Have you ever thought about the type of protection each switch provides in circuits? What kind of protection does each switch offer?
To answer these questions, we need to examine the specifications of each switch and the type of protection it provides in the circuit. So, it’s better to familiarize ourselves with the specifications of each switch step by step to better understand their differences:
What is a Miniature Circuit Breaker (MCB)?
The Miniature Circuit Breaker (MCB), also known as a miniature breaker, is one of the types of electrical switches, abbreviated as MCB, which stands for Miniature Circuit Breaker. In the traditional market, it is also referred to as a miniature fuse, although scientifically, this term is incorrect because a fuse is a one-time-use device, while a miniature circuit breaker can be operated multiple times.
Usually, the Miniature Circuit Breaker can withstand currents below 100 amperes and does not have any adjustable capabilities. It is used in places where the possibility of excess current exists to protect against overcurrent faults. Additionally, Miniature Circuit Breakers typically have a breaking capacity of 6 to 10 kiloamperes.
Double-pole breakers can be used in two modes: 1. One phase plus neutral. 2. Two phases.
Unfortunately, accessories for these breakers are not available in Iran. These switches are available in the market in single-pole, double-pole, triple-pole, and four-pole configurations with protection on all poles.
There is a mechanical connection between all these poles, and they are used for light residential purposes, lighting circuits, and wiring.
What is an Isolator or Dry Switch?
Another type of switch is the dry switches or isolators. Isolators, also known as dry electrical switches, are a subset of miniature circuit breakers but do not provide any protection themselves.
In reality, these types of switches are mostly used as isolators or disconnectors between a miniature circuit breaker (for circuit protection) and the load. They facilitate easy disconnection of the circuit when maintenance and load inspection are required. This ensures safety in case of unauthorized connections since the breaker has already disconnected the current flow.
What is a Compact Switch or Molded Case Circuit Breaker (MCCB)?
Another type of switch is the compact switches. The automatic switch or compact switch, abbreviated as MCCB (molded case circuit breaker), is one of the most popular types of electrical switches in the market.
The operation of the automatic switch is such that if suddenly faced with overload or short circuit in the cables, this switch can be used. The speed of disconnection varies depending on the load and is used for high current and low voltage applications.
These switches are used for protection against temperature rise and fault current and have high disconnection power. They are available in models ranging from a few amps to several thousand amps.
Compact switches are available in single-pole to four-pole configurations and are mostly used in the industry.
Unlike miniature switches, they have remote control capabilities. Under-voltage coils, trip shunts, and auxiliary contacts can be added to them. In fact, these relays are installed inside the switches. However, some switches are designed only to use one of these coils.
Automatic switches come in various configurations, such as three-pole or four-pole. The choice between them depends on their application and the level of protection required.
Certainly, opting for a four-pole automatic switch is more reasonable due to the additional protection it provides not only on the three phases but also on the neutral. However, unfortunately, four-pole switches are rarely available in the market, and three-pole switches are commonly used instead.
In compact switches, interlocks can be utilized for additional protection inside the switchboard. All auxiliary equipment is housed within the switch, and no separate unit needs to be installed on the switch.
Ultimately, when selecting an automatic switch, factors such as rated current, short-circuit breaking capacity, insulation voltage, the purpose of selecting the switch (type of protection required), installation status (whether it’s drawer-type or fixed), the number of poles, trip units required, and environmental conditions should all be taken into consideration. Only after evaluating these factors should we proceed with choosing the appropriate automatic switch.
The difference between shunt trip relays and undervoltage relays lies in their functionality, despite their similar physical appearance. When there is a need to interrupt a compact switch with an electrical command, these relays are utilized.
For instance, in a fire suppression system, by applying an electrical signal to the relay, the circuit breaker will be tripped for additional protection. These relays can be employed for various commands of this nature.
An undervoltage relay operates when the voltage falls below a specified level. Unlike a shunt trip relay, it remains energized, and when the voltage drops below the predetermined threshold, it will trip the breaker for enhanced protection.
Now, regarding air circuit breakers (ACB), they are a type of electrical switch available in the market for current ranges from several hundred to several thousand amperes. They are known as air circuit breakers because they extinguish arcs within a chamber of air.
These switches have adjustable settings, even in delays and trip thresholds, making them highly suitable for protecting sensitive equipment. They feature electronic control and sometimes incorporate microprocessors, allowing commands to be issued to the breaker via a network or remotely, enabling it to be tripped and reset.
Air circuit breakers (ACBs) possess extremely high current interruption capabilities, making them particularly useful in providing maximum protection for power plants.
Now, let’s delve into the Residual Current Circuit Breaker (RCCB). This type of electrical switch operates by comparing the phase and neutral currents. If there’s an imbalance between these two currents (indicating current leakage to ground), the RCCB detects this imbalance and cuts off the current within 30 seconds to protect the circuit.
RCCBs are primarily used to protect circuits with currents of 10 and 30 milliamperes. This level of current is so low that it prevents the occurrence of dangerous shocks.
Sudden changes in electrical loads can lead to short-circuit currents to ground, especially in older appliances. For instance, when the motor of an old freezer turns off, the switch quickly cuts off the current. These switches are highly sensitive and act swiftly to maintain the desired level of protection.
What type of switch is an RCBO or a combination Residual Current Circuit Breaker with Overcurrent Protection? Residual Current Circuit Breaker devices are not used for protecting against overload currents; rather, their function is solely to detect phase and neutral current imbalances. Therefore, these switches cannot be used to protect against overcurrent faults or short circuits of any magnitude because they lack the ability to detect such faults and could potentially lead to disastrous outcomes.
It is advisable to use an RCCB switch alongside an MCB switch in the fuse box. The combination of these two switches creates an RCBO (Residual Current Circuit Breaker with Overcurrent Protection), which combines the functionalities of both switches, including protection against overload currents.
What is the difference between the operation of a fuse and a miniature circuit breaker (MCB)?
Fuses and miniature circuit breakers are classified as types of electrical switches based on their amperage rating. The amperage rating indicated on the body of a fuse or miniature circuit breaker represents the continuous current that they can handle, known as their nominal current.
Many people believe that if the current exceeds slightly above the nominal current, the device (fuse or miniature circuit breaker) will immediately trip. Therefore, if the current rating of a switch or fuse is 30 amps, a current of 30.0001 amps would cause the switch to trip. What is your opinion on this matter?
In reality, such an incident does not occur. Fuses and miniature circuit breakers have significantly different properties, even if they have the same nominal current rating. Their protective limits are distinct.
Consider a 32-ampere miniature circuit breaker and a 32-ampere fuse, for instance. For definite tripping within 0.1 seconds, the miniature circuit breaker requires a current of 128 amperes, whereas the fuse requires 300 amperes.
It is evident that the fuse requires a higher current, but note that both currents are significantly higher than the nominal current, which is 30 amperes. It is highly unlikely that a 30-ampere fuse would trip at a current of around 30.0001 amperes.
Sometimes, people mistakenly use the term “miniature fuse” instead of “miniature circuit breaker.” However, as we know, miniature circuit breakers have the capability of being reset, whereas fuses burn out after tripping and become practically unusable. Thus, a new fuse needs to be installed. Consequently, fuses are considered one-time-use devices, while miniature circuit breakers can be used repeatedly. Therefore, the names of these two devices cannot be used interchangeably.
In conclusion
all switches can be categorized based on the type of protection and the range of operation, making it easy to select the appropriate switch. We hope that we have been able to assist you in choosing the desired switch more easily…
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