What Type Of Safety Devices Are Used In Electric Circuits
Fuse – Among the all other protection devices of electrical circuit fuse has its unique purposes. It protects the current from overcurrent through its metal strip which is to liquefy the current when the flow is high. Nowadays, various categories are useful in various applications such as response time, breaking capacity, current ratings, and specific voltage.

What are the safety devices for an electric circuit?

Figure 1: A fuse box in a basement is one type of electrical safety device. Many of the energy services around the house use electricity. It is extremely important to have various safety devices to protect from fire and electrocution. Industrial electricity use has similar problems.

What are the three basic types of circuit protection devices?

Residual Current Device (RCD), Residual Current Circuit Breaker (RCCB), Ground Fault Circuit Interrupter (GFCI) – In earthed electrical systems, (UK mains and many other countries) it is possible to fit a further form of protection, since any current flowing ‘out’ of the live should be definition exactly match the ‘return’ on the neutral, any imbalance between these two values constitutes a fault.

  • A Residual Current Device (RCD) uses an electronic circuit to detect even the smallest imbalance between the live and neutral conductors and if it reaches a trigger level disconnects the circuit.
  • Again this disconnect is in the order of milliseconds and RCD’s can be specified to sense fault levels as low as 5mA ( typically 30mA ).

In modern electrical circuits many devices contain filtering circuits for EMC compliance, some of these circuits contain deliberate ‘Earth Leakage’ leading to nuisance trips of RCD’s. A great deal of confusion is caused by the fact that both Magnetic and Thermal-Magnetic circuit breakers are called MCB’s, in addition it is possible to get a combined MCB and RCCB in one device (Residual Current Breaker with Overload RCBO), the principals are the same, but more styles of disconnection are fitted into one package.

What are types of circuit protection?

There are two general categories of circuit protection: 1) Fuses 2) Electro-mechanical circuit breakers. Each has its advantages which will be discussed here. Fuses break down into three convenient categories —fast-blow, slow- blow, and semiconductor. Each responds to fault current in different ways.

What is an example of a safety device?

A safety device is a piece of equipment such as a fire extinguisher, safety belt, or burglar alarm that reduces loss or damage from a fire, accident, or break-in.

What is a protective device in electrical?

Electrical Protection Devices and Control – AutomationForum A device used to protect equipment,machinery,components and devices,in electrical and electronic circuit,against short circuit,over current and earth fault,is called as protective devices.

What are the four types of electrical protections?

Think Panel. Think Rishabh! – Published Sep 8, 2021 Introduction: With an increasing of an electrical demand, it is essential to have a continuous healthy electrical power supply in any industry, where interruption of this power results in interruptions in industrial process which has huge commercial impact.

  1. This interruption is not necessarily due to the power outage.
  2. But it mostly happens due to various faults that occur in the system.
  3. Deteriorated quality of supply due to unforeseen faults like short circuits, over-voltages, and phase failures may lead to a reduction in performance, operational efficiency of equipment, or complete shutdown.

Thus, it is crucial to implement necessary measures to prevent the occurrence of these faults in the system. However, if the faults, still occur, it is crucial to provide electrical safety and minimize the potential damage to life, equipment, and property.

Over and Under Voltage fault – An under-voltage is a condition when the system voltage goes below the equipment nominal working voltage resulting in equipment failure e.g. motors. This means when system voltage goes below nominal rating, the load current will increase and power carrying capacity of the system decrease. An over-voltage is a condition when the system voltage goes above transformer, capacitor, motor, generator, or reactor voltage rating. Over-voltages can lead to equipment failure, such as the failure of a load tap changer controller resulting in a sudden disconnection of consumer load. These faults mostly occur due to sudden loss of load, Failure of voltage regulators, and Increase in system capacitance.

Phase failure and phase unbalance – Phase unbalance is the condition when the voltage across the three phases is not equal. In this case, current through the equipment increases which may lead to failure of equipment, generally in case of balanced loads like 3 phase motors. On the other hand, Phase Failure may occur due to a blown fuse, a mechanical failure of the switching equipment, or due to single phasing.E.g. If one phase gets disconnected in a 3 phase 3 wire or 4 wire system, it is identified as a loss of phase or single phasing condition.

Under-current and Over-current Fault – Undercurrent can occur if there is a fault with the power supply, or if a loaded motor becomes unloaded. Under-current relay trips the supply connection when the load current goes below the set-point value. Often an over-voltage situation will cause undercurrent which causes damage to the load equipment. Over-current can be caused by either the load or the supply such as a sudden increase in load due to faulty electronic or physical load on a motor. Additionally, a voltage drop could also cause an over-current situation. Over-current relay trips the supply when the load current crosses the set-point limit of the connected load. Neutral Failure – If the neutral conductor is open or damaged either at load or source side, it loses its reference ground point. This condition, called floating neutral, can cause voltages to reach maximum RMS phase voltages subjecting to unbalanced load condition. Neutral failure occurs due to poor installation at three-phase distribution transformer, broken neutral conductor, High earth resistance of a neutral conductor, or overloading of neutral.

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Protection devices: System protection is the art and science of detecting problems with power system components and isolating them from the rest of the healthy system during the fault occurrence. There are different protection devices like Fuse, Circuit Breaker (MCB, MCCB, and ACB), and Protection Relays. But these devices have different nature of operation.

Fuse – Fuse is used against the over-current protection. It consists of a metal strip, which melts down when an over-current condition occurs. Every time user has to replace the fuse wire to connect the load to the supply. Circuit breaker – CB is used to provide protection against short circuit current or from the over current. It basically disconnects or trips the supply connection once the fault occurred in the system. Unlike a fuse, a circuit breaker can operate automatically as well as manually to restart the supply. The circuit breaker senses the signal from the relay and then trips the supply. Circuit breakers are instantaneous operating devices. Depending on the type of application circuit breakers are categorized as MCB, MCCB, RCCB, ACB, and VCB. Protection Relay – Protection relay does not break the supply connections directly. It simply monitors the abnormal condition of the system and sends a tripping signal to the circuit breaker. Further, the circuit breaker trips the connections and this is how protection is provided by a relay. There are different types of relays for the system protection like Voltage Relay, Current Relay, Line Monitoring Relay, Earth Fault Relay, Earth Leakage Relay, and Motor Protection Relays. Relay detects unhealthy system lines, apparatus/equipment and then initiates the appropriate control circuit action. They have inbuilt electro-mechanical or electronic circuitry for protection function. Relays are of different types e.g. Definite Time Relays and Inverse Definite Time (IDMT) Relays. Relays use in substations is IDMT type that is an inverse definite time, whereas in LT panels definite time relay are preferred.

In case of definite time relays, when a fault occurs, relay tripping can take place after user-defined time, which may vary from 1 sec to 15 secs. Rishabh’s Contribution: Rishabh basket includes programmable digital as well as static type protection relays that monitor the system to protect it against various types of faults mentioned previously.

Rish Relay V and VR protect the system from Over and under voltage fault condition along with phase failure, phase unbalance, incorrect phase sequence, and neutral failure. Similarly, Rish Relay I and AR protect the system against over and under current fault along with current unbalance. Rish Relay PHR protects the system from phase failure, phase unbalance, and the incorrect phase sequence.

Application areas of these relays are in below industries:  Automotive industry  HVACR (Air conditioning and compressors)  Food and chemical industry  AMF / MCC panels  Lighting and control Author – Mr. Rahul Pansare, Business Promoter – Digital Expertise Website: https://rishabh.co.in/

What are most circuit control devices?

Electrical Fundamentals – Introduction to Circuit Control Devices – a PDH Online Course for Engineers Electrical Fundamentals – Introduction to Circuit Control Devices, B.E. Course Outline Many electrical devices are used some of the time and not needed at other times.

  • Remove power from a malfunctioning device
  • Apply power to a device when work is completed on it
  • Select the function or circuit desired within a device

This course provides you with insight to what circuit control devices are, how they are used, and some of their characteristics. This 3-hr course material is based entirely on Naval Education and Training Materials (NAVEDTRA 14175), Electricity and Electronic Training Series; Module-3 “Circuit Control Devices” and covers Chapter 3.

  • State three reasons circuit control devices are used and list three general types of circuit control devices;
  • State the difference between a manual and an automatic switch and give an example of each;
  • State the reason multi-contact switches are used;
  • State the characteristics of a switch described as a rocker switch;
  • State the possible number of positions for a single-pole, double-throw switch;
  • State the type of switch used to prevent the accidental energizing or de-energizing of a circuit;
  • State the meaning of the current and voltage rating of a switch;
  • State the operating principle of a relay and how it differs from a solenoid; and
  • State the ways in which the circuit control devices can be checked for proper operation and the procedure for servicing it.
  • Intended Audience
  • This course is aimed at students, professional electrical & electronics engineers, service technicians, energy auditors, operational & maintenance personnel, facility engineers and general audience.
  • Course Introduction

Circuit control, in its simplest form, is the application and removal of power. This can also be expressed as turning a circuit on and off or opening and closing a circuit. Before you learn about the types of circuit control devices, you should know why circuit control is needed.

  1. In essence, a circuit control device makes possible the selection of the particular circuit you wish to use.
  2. Course Introduction
  3. In this course, you are required to study Naval Education and Training Materials (NAVEDTRA 14175), Electricity and Electronic Training Series; Module-3, Chapter 3 titled “Circuit Control Devices”:

Please click on the above underlined hypertexts to view, download or print the documents for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing “Save Target As,”, and then open the file in Adobe Acrobat Reader.

  • Course Summary Circuit control devices are used to “turn on” and “turn off” current flow in an electrical circuit.
  • Circuit control devices have many different shapes and sizes, but most circuit control devices are switches, solenoids or relays.
  • A switch is the most common circuit control device.
  • Switches normally have two or more sets of contacts.

Opening these contacts is called “break” or “open” the circuit, closing the circuit is called “make” or “completing” the circuit. Switches are described by number of poles and throws they have. Poles refer to the number of input circuit terminals while throws refers to the number of output circuit terminal.

They are further referred to as SPST (single pole, single throw), SPDT (single pole, double throw) or MPMT (multi-pole, multi-throw). A relay is a simple remote control switch, which uses small amount of current to control a large amount of current. Its construction contains an iron core, electromagnetic coil and an armature.

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The iron core intensifies the magnetic field, which attracts the upper contact arm and pulls it down; thus closing the contacts and allowing power from the power source to go to the load. An example would be a computer, which controls a relay, and the relay controls a higher current circuit.

  • Quiz
  • Once you finish studying the above course content, you need to to obtain the PDH credits,

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice.

What are the names of two circuit protection devices?

Overcurrent Protection and Overcurrent Protection Devices Overcurrents and protective devices are not new subjects. Soon after Volta constructed his first electrochemical cell, or Faraday spun his first disk generator, someone else graciously supplied these inventors with their first short circuit loads.

  1. Patents on mechanical circuit-breaking devices go back to the late 1800’s and the concept of a fuse goes all the way back to the first undersized wire that connected a generator to a load.
  2. In a practical sense, we can say that no advance in electrical science can proceed without a corresponding advance in protection science.

An electric utility company would never connect a new generator, a new transformer, or a new electrical load to a circuit that cannot automatically open by means of a protective device. Similarly, a design engineer should never design a new electronic power supply that does not automatically protect its solid-state power components in case of a shorted output. Examples of are many: fuses, electromechanical circuit breakers, and solid state power switches. They are utilized in every conceivable electrical system where there is the possibility of overcurrent damage. As a simple example, consider the typical industrial laboratory electrical system shown in Figure 1.1.

  • We show a one-line diagram of the radial distribution of electrical energy, starting from the utility distribution substation, going through the industrial plant, and ending in a small laboratory personal computer.
  • The system is said to be radial since all branch circuits, including the utility branch circuits, radiate from central tie points.

There is only a single feed line for each circuit. There are other network type distribution systems for utilities, where some feed lines are paralleled. But the radial system is the most common and the simplest to protect. Overcurrent protection is seen to be a series connection of cascading current-interrupting devices.

  • Starting from the load end, we have a dual-element or slow-blow fuse at the input of the power supply to the personal computer.
  • This fuse will open the 120 volt circuit for any large fault within the computer.
  • The large inrush current that occurs for a very short time when the computer is first turned on is masked by the slow element within the fuse.

Very large fault currents are detected and cleared by the fast element within the fuse. Protection against excess load at the plug strip, is provided by the thermal circuit breaker within the plug strip. The thermal circuit breaker depends on differential expansion of dissimilar metals, which forces the mechanical opening of electrical contacts.

  • The 120 volt single-phase branch circuit, within the laboratory which supplies the plug strip, has its own branch breaker in the laboratory’s main breaker box or panel board.
  • This branch breaker is a combination thermal and magnetic or thermal-mag breaker.
  • It has a bi-metallic element which, when heated by an overcurrent, will trip the device.

It also has a magnetic-assist winding which, by a solenoid type effect, speeds the response under heavy fault currents. All of the branch circuits on a given phase of the laboratory’s 3-phase system join within the main breaker box and pass through the main circuit breaker of that phase, which is also a thermal magnetic unit.

  1. This main breaker is purely for back up protection.
  2. If, for any reason, a fails to interrupt overcurrents on that particular phase within the laboratory wiring, the main breaker will open a short time after the branch breaker should have opened.
  3. Back-up is an important function in overload protection.

In a purely radial system, such as the laboratory system in Figure 1.1, we can easily see the cascade action in which each overcurrent protection device backs up the devices downstream from it. If the computer power supply fuse fails to function properly, then the plug strip thermal breaker will respond, after a certain coordination delay.

If it should also fail, then the branch breaker should back them both up, again after a certain coordination delay. This coordination delay is needed by the back-up device to give the primary protection device – the device which is electrically closest to the overload or fault – a chance to respond first.

The coordination delay is the principal means by which a back-up system is selective in its protection. Selectivity is the property of a protection system by which only the minimum amount of system functions are disconnected in order to alleviate an overcurrent situation.

  1. A power delivery system which is selectively protected will be far more reliable than one which is not.
  2. For example, in the laboratory system of Figure 1.1, a short within the computer power cord should be attended to only by the thermal breaker in the plug strip.
  3. All other loads on the branch circuit, as well as the remaining loads within the laboratory, should continue to be served.

Even if the breaker within the plug strip fails to respond to the fault within the computer power cord, and the branch breaker in the main breaker box, is forced into interruptive action, only that particular branch circuit is de-energized. Loads on the other branch circuits within the laboratory still continue to be served.

In order for a fault within the computer power cord to cause a total blackout within the laboratory, two series-connected breakers would have to fail simultaneously – the probability of which is extremely small. The ability of a particular overcurrent protection device to interrupt a given level of overcurrent depends on the device sensitivity.

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In general, all overcurrent protection devices, no matter the type or principles of operation, respond faster when the levels of overcurrent are higher. Coordination of overcurrent protection requires that application engineers have detailed knowledge of the total range of response for particular protection devices. This information is contained in the “trip time vs. current curves,” commonly referred to as the trip curves.

A trip time-current curve displays the range of, and the times of response for, the currents for which the device will interrupt current flow at a given level of circuit voltage. For example, the time current curves for the protection devices in our laboratory example are shown superimposed in Figure 1.2.

The rated current for a device is the highest steady-state current level at which the device will not trip for a given ambient temperature. The steady-state trip current is referred to as the ultimate trip current. The ratings for the dual-element fuse in the computer power supply, the plug strip thermal breaker, the branch circuit thermal-magnetic breaker and the main circuit thermal-magnetic breaker are 2, 15, 20, and 100 amps, respectively.

  • Note that, except for the fuse curve, each time-current curve is shown as a shaded area, representing the range of response for each device.
  • Manufacturing tolerances and material property inconsistencies are responsible for these banded sets of responses.
  • Trip time-current information for small fuses is usually represented in a single-value average melting time curve.

Even with a finite width to the time-current curves, we can easily see the selectivity/coordination between the different protection devices. For any given steady-state level of overcurrent, we read up the trip time-current plot, at that level of current, to determine the order of response.

Consider the following three examples for the laboratory wiring, plug strip, and computer system. Example 1: Component failure within the computer power supply: Assume that a power component within the computer power supply has failed – say two legs of the bridge power rectifier – and that the resulting fault current within the supply, limited by a surge resister, is 70 amps.

We see from the fuse trip curve that it should clear this level of current in approximately 20 milliseconds. If the fuse fails to interrupt the current – or worse, if the fuse has been replaced with a permanent short circuit by a gambling repairperson – the thermal breaker in the plug strip should open the circuit within 0.6 to 3.5 seconds.

  • The branch thermal-magnetic breaker will open the entire branch circuit within 3.5 to 7.0 seconds, should the plug strip thermal breaker also fail to respond.
  • Note that no back-up is provided for this particular fault after the branch circuit breaker.
  • The main laboratory 100 amp thermal-magnetic unit would respond only if the other loads within the entire laboratory totaled greater than 30 amps at the time of the 70 amp power supply fault.

Example 2: Plug strip overload: Assume that the computer operator has spilled a drink, and to dry up the mess plugs two 1500 watt hair dryers into the plug strip. The operator then flips them both on simultaneously, drawing a total plug strip load current of approximately 30 amps.

  • From the thermal breaker trip curve, we see that the plug strip unit should clear this overload within 5 to 30 seconds.
  • Note the similarity between the trip curves of the plug strip thermal unit and the branch circuit thermal-magnetic unit in the region of 100 amps and below.
  • This is because, for these levels of currents, the thermal portion of the detection mechanism within the thermal-magnetic branch breaker is dominant.

Example 3: Short circuit within the computer power cord: Assume a frayed line cord finally shorts during some mechanical movement. Assume also that there is enough resistance within the circuit, plug strip, and line cord system to limit the resulting fault current to 300 amps.

  • This level of current is 2000% (20 times) of the rated current of the plug strip thermal breaker, and is beyond the normal range of published trip time specifications for thermal breakers (100% to 1000% of rated current).
  • Thus the exact trip time range of the thermal unit is indeterminate.
  • At high levels of fault current, greater than 150 amps in this case, we can see the inherent speed advantage of magnetic detection of overcurrents.

This is evidenced by the fact that the response curve for the thermal-magnetic branch circuit breaker knees downward sharply at current levels between 150 and 200 amps. At these and higher currents, the magnetic detection mechanism within the thermal-magnetic unit is dominant.

The response curve for the unit crosses over the plug strip thermal breaker response curve (assuming that it extends past its 1000% limit), and coordination between the two interrupters is lost. The range of response for the thermal-magnetic breaker at 300 amps is 8 to 185 milliseconds. Should both the plug strip breaker and the branch circuit breaker fail to operate, the main laboratory breaker should clear the fault within 11 to 40 seconds.

: Overcurrent Protection and Overcurrent Protection Devices

What are the two most common methods of circuit protection?

The two most common methods of circuit protection in structures are fuses and circuit breakers.

Which device is used as protection from over current?

Plug-in fuses are used to protect a circuit board from overcurrent conditions. A glass fuse can be used as a plug-in fuse or in a fuse holder.

Is a circuit breaker a protection device?

A circuit breaker is an electrical switch designed to protect an electrical circuit from damage caused by overcurrent/overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault.

What are the 5 types of circuits?

There are 5 Main Types of Electric Circuit – Close Circuit, Open Circuit, Short Circuit, Series Circuit and Parallel Circuit. Learn in Detail. There are 5 Main Types of Electric Circuit – Close Circuit, Open Circuit, Short Circuit, Series Circuit and Parallel Circuit. Let us Learn and Understand in Detail with Definition, Examples and Symbols.

What are the most common methods of circuit protection in structures?

➢ Fuses and Circuit Breakers Both fuses and circuit breakers are ‘over- current’ devices used to prevent fires and damage to wiring and equipment caused by an excessive flow of current.