CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

. Different techniques are used to extinguish the arc including:

Circuit breakers are rated both by the normal current that they are expected to carry, and the maximum short-circuit current that they can safely interrupt.

Under short-circuit conditions, a current many times greater than normal can exist (see maximum prospective short circuit current). When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. This condition can create conductive ionized gases and molten or vaporized metal, which can cause further continuation of the arc, or creation of additional short circuits, potentially resulting in the explosion of the circuit breaker and the equipment that it is installed in. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc

Lengthening / deflection of the arc Intensive cooling (in jet chambers) Division into partial arcs

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Zero point quenching (Contacts open at the zero current time crossing of the AC waveform, effectively breaking no load current at the time of opening. The zero crossing occurs at twice the line frequency, i.e. 100 times per second for 50 Hz and 120 times per second for 60 Hz AC)

Connecting capacitors in parallel with contacts in DC circuits.

Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.

Standard current ratingsCircuit breakers are manufactured in standard sizes, using a system of preferred numbers to cover a range of ratings. Miniature circuit breakers have a fixed trip setting; changing the operating current value requires changing the whole circuit breaker. Larger circuit breakers can have adjustable trip settings, allowing standardized elements to be appplied but with a setting intended to improve protection. For example, a circuit breaker with a 400 ampere "frame size" might have its overcurrent detection set to operate at only 300 amperes, to protect a feeder cable.

International Standard--- IEC 60898-1 and European Standard EN 60898-1 define the rated current In of a circuit breaker for low voltage distribution applications as the maximum current that the breaker is designed to carry continuously (at an ambient air temperature of 30 °C). The commonly-available preferred values for the rated current are 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A, 100 A,[5] and 125 A (Renard series, slightly modified to include current limit of British BS 1363 sockets). The circuit breaker is labeled with the rated current in amperes, but without the unit symbol "A". Instead, the ampere figure is preceded by a letter "B", "C" or "D", which indicates the instantaneous tripping current — that is, the minimum value of current that causes the circuit breaker to trip without intentional time delay (i.e., in less than 100 ms), expressed in terms of In:

Type Instantaneous tripping currentB above 3 In up to and including 5 In

C above 5 In up to and including 10 In

D above 10 In up to and including 20 In

K

above 8 In up to and including 12 In

For the protection of loads that cause frequent short duration (approximately 400 ms to 2 s) current peaks in normal operation.

Z

above 2 In up to and including 3 In for periods in the order of tens of seconds.

For the protection of loads such as semiconductor devices or measuring circuits using current transformers.

Circuit breakers are also rated by the maximum fault current that they can interrupt; this allows use of more economical devices on systems unlikely to develop the high short-circuit current found on, for example, a large commercial building distribution system

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In the United States, Underwriters Laboratories (UL) certifies equipment ratings, called Series Ratings (or “integrated equipment ratings”), using a two-tier rating. For example, a 22/10 rating. This rating means that the meter pack has a 22 kAIC tenant breaker, feeding a 10 kAIC loadcenter with 10 kAIC branches, where kAIC stands for “Thousand Ampere Interrupting Capacity.” Common meter pack ratings are 22/10, 42/10 and 100/10.[6]

Types of circuit breakers

Front panel of a 1250 A air circuit breaker manufactured by ABB. This low voltage power circuit breaker can be withdrawn from its housing for servicing. Trip characteristics are configurable via DIP switches on the front panel.

Many different classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features.

Magnetic circuit breakers

Magnetic circuit breakers use a solenoid (electromagnet) whose pulling force increases with the current. Certain designs utilize electromagnetic forces in addition to those of the solenoid

Thermal magnetic circuit breakers

Thermal magnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions. The thermal portion of the circuit breaker provides an "inverse time" response feature, which trips the circuit breaker sooner for larger overcurrents.[7]

Fuses

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

In electronics and electrical engineering, a fuse (from the French fuser, Italian fuso, "spindle"[1]) is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, interrupting the circuit that it connects. Short circuits, overloading, mismatched loads, or device failure are the prime reasons for excessive current. Fuses are an alternative to circuit breakers.

The I2t value

The amount of energy spent by the fuse element to clear the electrical fault. This term is normally used in short circuit conditions and the values are used to perform co-ordination studies in electrical networks. I2t parameters are provided by charts in manufacturer data sheets for each fuse family. For coordination of fuse operation with upstream or downstream devices, both melting I2t and clearing I2t are specified. The melting I2t, is proportional to the amount of energy required to begin melting the fuse element. The clearing I2t is proportional to the total energy let through by the fuse when clearing a fault. The energy is mainly dependent on current and time for fuses as well as the available fault level and system voltage. Since the I2t rating of the fuse is proportional to the energy it lets through, it is a measure of the thermal damage and magnetic forces that will be produced by a fault.

The I2t value

The amount of energy spent by the fuse element to clear the electrical fault. This term is normally used in short circuit conditions and the values are used to perform co-ordination studies in electrical networks. I2t parameters are provided by charts in manufacturer data sheets for each fuse family. For coordination of fuse operation with upstream or downstream devices, both melting I2t and clearing I2t are specified. The melting I2t, is proportional to the amount of energy required to begin melting the fuse element. The clearing I2t is proportional to the total energy let through by the fuse when clearing a fault. The energy is mainly dependent on current and time for fuses as well as the available fault level and system voltage. Since the I2t rating of the fuse is proportional to the energy it lets through, it is a measure of the thermal damage and magnetic forces that will be produced by a

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a.) b.c 0.) c.) d.)

a.) Electrical resettable screw type fuse low voltage D0 series According to DIN VDE 0636, IEC 269 Rated voltage: AC 400V, DC 250V Operating class gL/gG For cable and line protection Finely ..

b.) Glass tube fuse. Tube fuse, fast blow, slow blow, electrical fuse Operation: Manual Type Installation: Open Frame Speed: Normal Type Circuit Breaker Structure: Moulded Case Circuit Breaker .

c. ) HRC NH type ceramic low voltage fuse: Type No: NH000, NH00, NH00C, NH0, NH1, NH1C, NH2, NH2C, NH3, NH3C, NH4, NH4C Rated Current: 4A-630A Rated Voltage: 500/660V Confirm to GB13539 and ..

d.) Low voltage knife NH fuse holder: Rated insulating voltage(V): 660 Rated thermal current(A): 250, 400, 630 Type: NT1/NT2/NT3.

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

Z-1061Main Service Conductor Cable Limiters (N.E.C. 240, 450-6):a) Select by cable size and mounting terminal configurations required.2Main Service Circuit Fuses–Mixed Loads:a) Size fuses same as item 6.3Transformer Circuit Fuses (N.E.C. 450-3b, 240-3, 240-21, 384-16d, 430-72b Ex. 3, 4 & (c) as required):*a) PRIMARY FUSES: Size fuses not over 125%. As exceptions exist, refer to the appropriate N.E.C. paragraphs. Recommended fuses: LESRK, ECSR, JDL,LCL+.*b) SECONDARY FUSES (Sum of following): 125% of the continuous load plus 100% of non-continuous load. Fuse size not to exceed 125% of transformer secondary rated amps. RECOMMENDED FUSES: LENRK, ECNR, NCLR, JDL or LCU.*Fuse size must not exceed ampacity of conductors. Where selectivity is desired, refer to EDISON selectivity methods.

FUSE SIZING GUIDE4Branch Circuit FuseSize, No Motor Load (N.E.C. 240-3, 220-3):*a) 100% of non-continuous load.*Do not exceed conductor ampacity. Recommended fuses: LENRK, ECNR, NCLR, JDL, LCU, or LCL.5Branch Circuit Fuse Size, No Motor Load(N.E.C. 240-3, -220-3):*a) 125% of continuous load. Fuse may be sized 100% when used with a continuous rated switch. Recom-mended fuses

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

same as 4.*Do not exceed conductor ampacity.6Feeder Circuit Fuse Size, Mixed Load (N.E.C. 220-10b, 240-3, 430-22a Ex. 1, 430-24):*a) 100% of non-continuous, non-motor load plus 125% of continuous, non-motor loadb) Determine non-continuous motor load (N.E.C. 430-22a EX. Add to "a)" above.c) Determine A/C or refrigeration load. (N.E.C. 440-3b). Add to "a)" above.d) 150% of the nameplate current rating of the largest continuous-duty motor. Add to "a)" above.e) 125% of the nameplate current rating of other continuous duty motors.Add to "a)" above.f) Recommended fuses: LENRK/LESRK,JDL, ECNR/ ECSR, LCU, LCL.*Do not exceed conductor ampacity.7Feeder Circuit Fuse Size, 100%Motor Load (N.E.C. 240-3, 220-10b, 430-24):*a) Determine non-continuous motorload (N.E.C. 430-22a Ex. 1).b) Determine load of A/C or refrigeration equipment (N.E.C. 440-3, -5, -12). Add to "a)" above.c)150% of nameplate current rating of the largest continuous duty motor. Add to "a)" above.d)125% of the other continuous-duty motors. Add to "a)" above.e)Recommended fuses: LENRK/LESRK,JDL, ECNR/ ECSR or LCL.*Do not exceed conducto

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

RELAYS

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.

Pole and throw

Circuit symbols of relays. (C denotes the common terminal in SPDT and DPDT types.)

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

Since relays are switches, the terminology applied to switches is also applied to relays; a relay switches one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways:

Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact. NO contacts may also be distinguished as "early-make" or NOEM, which means that the contacts close before the button or switch is fully engaged.

Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact. NC contacts may also be distinguished as "late-break" or NCLB, which means that the contacts stay closed until the button or switch is fully disengaged.

Change-over (CO), or double-throw (DT), contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact ("break before make"). If this type of contact utilizes a "make before break" functionality, then it is called a Form D contact.

The following designations are commonly encountered:

SPST – Single Pole Single Throw. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.

SPDT – Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

DPST – Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. The poles may be Form A or Form B (or one of each).

DPDT – Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.

The "S" or "D" may be replaced with a number, indicating multiple switches connected to a single actuator. For example 4PDT indicates a four pole double throw relay (with 12 terminals).

Relay types

a. Electromagnetic relay: General purpose relay, 60 hz 110 volt coil, DPDT contacts 25A at 300V AC..The transparency allows inspection of the contacts, coil, and swing arms for evidence of overheating.

b. Solid-state relays (SSR):SCR output solid state relays are designed for AC loads only, and exhibit tight, zero-volt switching. High dv/dt characteristics allow this type of device to control highly inductive loads (PF > 0.3).Main components: (AC-SSR)Triac, photo-transistor

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

Electromagnetic Relay

Contactor

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A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.[1] A contactor is controlled by a circuit which has a much lower power level than the switched circuit.

Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amperes to thousands of amperes and 24 V DC to many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side.

Contactors are used to control electric motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.

Contactor

a. AC-contactor

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

Switch contact

b. DC-contactors

are widely used in drive and control systems, electrical vehicle, moving excavation equipment, aircraft moving .

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

DC contactors

DC-contactor

SW200A 48DC CW -128 (13220173)

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

Push Buttons

Construction A push button switch is a small, sealed mechanism that completes an electric circuit

when you press on it. When it's on, a small metal spring inside makes contact with two wires, allowing electricity to flow. When it's off, the spring retracts, contact is interrupted, and current won't flow. The body of the switch is made of non-conducting plastic.

Momentary Contact

Momentary switches work only as long as you press on them, like the buttons on a phone, calculator or door buzzer. They can be subdivided into normally-on and normally-off types.

Normally-Off

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With the normally-off switch, there's no connection till you push the button. Most push button switches are used this way. Examples include doorbell buttons, cell phone keys and garage door openers.

Normally-On Here the switch conducts normally, but interrupts the circuit when you press on it. This is

more specialized, and may be used in conjunction with a wiring trick. For example, connecting a normally-on switch in parallel with a light bulb will light the bulb when the button's pushed; otherwise, current will flow through the switch, leaving the bulb off.

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CCE203:Engineering Workshop Electrical Panel Board Dr. Adel Chit

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