Electrical Installations SFU, MCB, MCCB, ELCB, TYPES OF WIRES AND CABLES

1. St. Martin's Engineering College
An autonomous institution
NBA&NACC A+ Accredited
Department of Electrical &Electronics Engineering
BEE_UNIT-V
ELECTRICAL INSTALLATIONS
By
N. DANIEL MANOJ
Assistant Professor

2. Contents:
 Components of LT Switchgear: Switch Fuse Unit (SFU), MCB, ELCB, MCCB,
 Types of Wires and Cables
 Electrical Safety precautions in handling electrical appliances, electric shock, first
aid for electric shock, safety rules.

3. Components of LT Switchgear: Switch Fuse Unit
(SFU), MCB, ELCB, MCCB
Switchgear: The apparatus used for switching, controlling and
protecting the electrical circuits and equipment is known as switchgear.
The term ‘switchgear’ is a generic term encompassing a wide range of
products like circuit breakers, switches, switch fuse units, off-load isolators,
HRC fuses, contactors, earth leakage circuit breaker, etc...

4. Components of LT Switchgear: Switch Fuse Unit
(SFU), MCB, ELCB, MCCB
Essential Features of Switchgear
The essential features of switchgear are :
1.Complete Reliability
2.Absolutely certain discrimination
3.Quick operation
4.Provision for manual control

5. Components of LT Switchgear: Switch Fuse Unit
(SFU), MCB, ELCB, MCCB
Classification of Switchgear:
Switchgear can be classified on the basis of voltage level into the following:
1. Low voltage (LV) Switchgear: upto 1KV
2. Medium voltage (MV) Switchgear: 3 KV to 33 KV
3. High voltage (HV) Switchgear: Above 33 KV

6. Components of LT Switchgear: Switch Fuse Unit
(SFU), MCB, ELCB, MCCB
Components of LT Switchgear:
The term LT Switchgear includes low voltage Circuit Breakers, Switches, off load
electrical isolators, HRC fuses, Earth Leakage Circuit Breaker, Miniature Circuit
Breakers (MCB) and Molded Case Circuit Breakers (MCCB) etc i.e. all the accessories
required to protect the LV system. The most common use of LV switchgear is in LV
distribution board.

7. Components of LT Switchgear: Switch Fuse Unit
(SFU), MCB, ELCB, MCCB
FUSE:
Fuse is a simplest and cheapest device used for interrupting an electrical
circuit under short circuit, or excessive overload, current magnitudes.
The action of a fuse is based upon the heating effect of the electric
circuit. The part which actually melts and opens the circuit is known as
the fuse element.
https://www.eeeguide.com/fuses-definition/

9. Components of LT Switchgear: Switch Fuse Unit
(SFU), MCB, ELCB, MCCB
The fuse has inverse time-current characteristics

10. Advantages:
•It is the cheapest form of protection available.
•It requires no maintenance.
•Its operation is inherently completely automatic unlike a circuit breaker which requires an
elaborate equipment for automatic action.
•It can break heavy short-circuit currents without noise or smoke.
•The smaller sizes of fuse element impose a current limiting effect under short-circuit
conditions.
•The inverse time-current characteristic of a Fuses Definition makes it suitable for over
current protection.
•The minimum time of operation can be made much shorter than with the circuit breakers.

11. Disadvantages:
•Considerable time is lost in rewiring or replacing a fuse after operation.
•On heavy short-circuits, discrimination between fuses in series cannot be obtained
unless there is sufficient difference in the sizes of the Fuses Definition concerned.
•The current-time characteristic of a fuse cannot always be co-related with that of
the protected apparatus.

12. FUSE UNITS:
The various types of fuse units, most commonly available are:
1. Round type fuse unit.
2. Kit-kat type fuse unit.
3. Cartridge type fuse unit.
4. HRC (High Rupturing Capacity) fuse units and
5. Semiconductor fuse units

13. 1. Round type fuse unit
 This type of fuse unit consists of a porcelain or bakelite box
and two separated wire terminals for holding the fuse wire
between them. This type of fuse is not common use on account
of its following disadvantages:
1. One of the terminals remain always energized and, therefore,
for replacement of fuse either the worker will have to touch the
live mains or open the main switch.
2. When the fuse blows off there is too much arcing and the unit
may be damaged. After two or three arcing the fuse unit becomes
unusable.T

14. 2. Rewirable or Kit-kat Type Fuses
 The most commonly used fuse in “house wiring’
and small current circuits is the semi-enclosed or
rewirable fuse (also sometimes known as kitkat
type fuse). It consists of a porcelain base carrying
the fixed contacts to which the incoming and
outgoing live or phase wires are connected and a
porcelain fuse carrier holding the fuse element,
consisting of one or more strands of fuse wire,
stretched between its terminals.

15. When fuse bridge with fuse element is inserted and the switch is made ‘on’ then only the
circuit is completed. These fuse units are rated as 5.15, 30 up to 300 Amps

16. Disadvantages of Rewirable or Kitkat
Type Fuses
• Unreliable operation.
• Lack of discrimination.
• Small time lag.
• Low rupturing capacity.
• No current limiting feature.
• Slow speed of operation.

17. 3. Cartridge Type Fuses
 This is a totally enclosed type fuse unit. It
essentially consists of an insulating
container of bulb or tube shape and sealed
at its ends with metallic cap known as
cartridge enclosing the fuse element and
filled with powder or granular material
known as filler. There are various types of
materials used asfiller like sand, calcium
carbonate, quartz etc. This type of fuse is
available upto 660V and the current rating
upto 800 A

18. 4. High Rupturing Capacity
(HRC) Fuses
 With a very heavy generating
capacities of the modern power
stations, extremely heavy currents
would flow into the fault and fuse
clearing the fault would be required to
withstand extremely high stresses in
this process.

19. Switch Fuse Unit (SFU):
Switch fuse is a combined unit and is known as an iron clad switch, being made of iron.
It may be double pole for controlling single phase two-wire circuits or triple pole for
controlling three-phase, 3-wire circuits or triple pole with neutral link for controlling 3-
phase, 4-wire circuits. The respective switches are known as double pole iron clad
(DPIC), triple pole iron clad (TPIC), and triple pole with neutral link iron clad (TPNIC)
switches.
DPIC

20. DPIC TPIC TPNIC

21. Switch Fuse Unit (SFU):
1. For Two-wire DC Circuits or Single Phase AC Circuits:
240V, 16A, DPIC switch fuse
2. For Three-Wire DC Circuits: 500V, 32A (63/100/150 or
higher amperes), IS approved TPIC switch fuse.
3. For Three-Phase Balanced Load Circuits: 415V, 32A
(63/100/150 or higher amperes), IS approved TPIC switch fuse.

23. Miniature Circuit Breaker (MCB):
A device which provides definite protection to the wiring installations and
sophisticated equipment against over-currents and short-circuit faults.
Thermal operation (overload protection) is achieved with a bimetallic
strip, which deflects when heated by any over currents flowing through it.
In doing so, releases the latch mechanism and causes the contacts to open.
Inverse-time current characteristics result. i.e. greater the overload or
excessive current, shorter the time required to operate the MCB.

26. Miniature Circuit Breaker (MCB):
On occurrence of short circuit, the rising current energizes the solenoid,
operating the plunger to strike the trip lever causing immediate release of the
latch mechanism. Rapidity of the magnetic solenoid operation causes
instantaneous opening of contacts. MCBs are available with different current
ratings of 0.5, 1.2, 2.5, 3, 4, 5,6, 7.5, 10, 16, 20, 25, 32, 35, 40, 63, 100, 125,
160 A and voltage rating of 240/415 V AC and up to 220 V DC. Operating
time is very short (less than 5 ms). They are suitable for the protection of
important and sophisticated equipment, such as air-conditioners, refrigerators,
computers etc.

28. Earth Leakage Circuit Breaker (ELCB):
 It is a device that provides protection against earth leakage.
 It is used when the product of the operating current in amperes and
the earth-loop impedance in ohms does not exceed 40. such circuit
breakers is used where consumer’s earthing terminal is connected to
a suitable earth electrode.

29. Earth Leakage Circuit Breaker (ELCB):

30. • An ELCB (Earth Leakage Circuit Breaker) is an electrical safety device
used to directly detect currents leaking to earth from an installation
and interrupt the power supply.
• Types
• ELCBs are two types.
• Voltage Earth Leakage Circuit Breaker (Voltage ELCB).
• Current Earth Leakage Circuit Breaker (Current ELCB).

31. • Current Earth Leakage Circuit Breaker
• The current ELCB is a circuit breaker that is commonly used. It is also
called RCCB (Residual Current Circuit Breaker).
• Principle of Operation
• The Current ELCB (or RCCB) consists of a three winding transformer,
which has two primary windings and one secondary winding. It is
called the Core Balance Current Transformer (CBCT).
• Phase and neutral wires act as the two primary windings. A wire-
wound coil is the secondary winding.

32. • At the balanced condition, the current through the secondary winding
is zero. For example, if the phase wire carries 5A means same 5 A
current will be returned to the neutral wire also.
• The sum of the current is zero. It is the normal state, in which the
current ELCB doesn’t get operated. Now consider a human touching a
phase wire, it causes current to pass from phase to earth.
• Now phase carries 5A (normal load) plus 30 mA of fault current. But
our neutral wire carries a 5A current.
• There is a difference of 30mA of current. It is sensed by the CBCT
(Core Balanced Current Transformer and send to the relay operating
coils.

33. • When a fault occurs, a small amount of current will flow to the ground
also. This makes an unbalance between phase and neutral currents and
creates an unbalanced magnetic field.
• This induces a current across the secondary winding, which is connected to
the sensing circuit. This will detect fault currents and send a signal to the
tripping system and trips the contact.
• Advantages
• Voltage-operated ELCB is less sensitive to fault conditions, therefore has
fewer nuisance trips.
• They do not detect faults that are don’t pass current through the circuit
protective conductor (CPC) to the earth rod.
• Current operated ELCB is not affected by parallel earth.
• Disadvantages
• Voltage-based ELCB devices are not used in the present days due to their
drawbacks as if the fault is between phase and circuit earth, they will
isolate the supply.

34. MCCB (Molded Case Circuit Breaker) –
Construction, Types & Working
• What is MCCB?
• Molded Case Circuit Breaker or MCCB is an automatic electrical
device. It is a type of circuit breaker that protects the circuit from
overloading, short circuit and current surges. It is an advanced version
of miniature circuit breaker MCB since it operates like one. However,
it offers extra features that make it a superior circuit breaker such as
remote closing and adjustable trip settings i.e. its current settings and
time settings can be adjusted according to our needs.

35. • MCCB is used to protect the low voltage distribution system. It is available
in rating up to 2500 Amps and 1.1 kV.
• Construction of Molded Case Circuit Breaker
• An MCCB is made from the following main parts each one explained in
detail
• Arc chute
• Contacts
• Operating mechanism
• Terminal Connector
• Thermal Trip Unit
• Magnetic Trip Unit
• Handle / Trip-free Mechanism
• Trip Button

37. • Below is the brief details of each mechanism used in a typical MCCB.
• Arc Chute
• Arc chute is a set of parallel metal plates that are mutually insulated from
each other. it helps in extinguishing the arc by splitting the arc and
lengthening it. it is also known as an arc divider or arc splitter. These plates
are made of ferromagnetic material.
• Contacts
• Contacts are the metallic conductors that are responsible for carrying the
current to the load. There are two types of contacts i.e. fixed and moving
contact. The contacts are made of arc resistance material having low
resistivity and corrosion. The quality of the material decides the lifetime of
the circuit breaker.
• Operating Mechanism
• It is the mechanism of MCCB responsible for opening and closing the
current-carrying contacts. it is connected with trip unit that triggers the
operating mechanism. The trip unit operates on a thermal and magnetic
mechanism.

38. • Terminal Connector
• The terminal connectors are used to connect the MCCB to the external
circuit. The upper terminals are connected to the output/load while the
bottom terminals are connected to the input/supply. Although they are
bidirectional, the input and output designation is due to their physical
installation
• Trip Unit
• It is the unit responsible to trigger the operating mechanism. The trip unit
includes a thermal mechanism for overload, magnetic tripping for short
circuits and a test button for testing.
• Thermal Trip Unit
• The thermal trip unit uses a thermal mechanism that is a bimetallic strip
that bends (and opens the contacts) when the temperature rises due to the
overloading.

39. • Magnetic Trip Unit
• The magnetic trip unit has a relay that generates a magnetic field when
higher currents flow through its solenoid due to the short circuit. it trips
the circuit breaker. While the test button is used to simulate the above-said
mechanisms and test the response of the circuit breaker.
• Handle / Trip-free Mechanism
• It is a handle used to open or close the breaker manually. It is also known
as a trip-free mechanism because it will trip even if the handle is held in
ON position.
• The handle could be in either three positions i.e. upward, middle or
downward. If the handle is in upward position, it is ON position. If it is in
the middle position, the breaker has been tripped while the downward
position shows OFF status.
• Trip Button
• The trip button is used for testing the breaker. It is a red-colored button
that trips the operating mechanism when pushed.

40. Working Principle of MCCB
• Overload Protection
• Overload occurs when the current exceeds a limit for a prolonged duration.
MCCB has a thermal mechanism that contains a bimetallic contact to
protect from overload. A bimetallic strip is made from two different types
of metal having different rates of thermal expansion. Upon temperature
change, the strip bends or contracts.
• The main current passes through the bimetallic strip. If the current exceeds
a certain limit, the contacts heat up and expand. Due to different
expansion rates, the strip bends and trips the circuit.
• In electrical devices, the current can overload for short durations of time, it
is normal and should not be considered as fault current. Therefore, MCCB
has a time delay that allows the overload current for a short duration of
time before tripping the circuit.

41. • Short Circuit Protection
• MCCB protects against a short circuits using a solenoid that produces
electromagnetic force. The main current flows through the solenoid
that attracts and repels a plunger responsible for tripping the breaker.
• If the current remains below the threshold, the solenoid produces a
weak magnetic force that cannot attract the plunger. In short circuit
conditions, a very high current flows through the solenoid that
generates a very strong magnetic force. It attracts the plunger that
trips the circuit.

42. • Advantages and Disadvantages of MCCB
• Advantages
• MCCB has an adjustable trip setting that allows it to be used for low
as well as large currents
• It can handle a very large current.
• It can instantly interrupt very large currents.
• It has a movable trip unit.
• It has a very small tripping time thus fast switching during fault
current.
• It also offers a remote ON/OFF feature.
• It has a compact design and takes less space.

43. • Disadvantages
• MCCB is not suitable for high voltage applications.
• They are not suitable for domestic applications.
• Applications of MCCBs
• Since MCCB can handle very high currents, they are used for heavy-duty applications such as in industries.
• Adjustable Trip Settings: MCCB is superior to MCB and has more application due to its higher current
handling and adjustable trip setting capabilities. It makes it versatile to be used for high as well as low
current settings.
• Motor Protection: MCCB is used in industries to protect large electrical motors from overloading. It offers
adjustable trip settings to tolerate the high inrush current with necessary delay.
• Welding Machine Protection: Welding machines draw a very large amount of current that an MCB cannot
handle. Therefore, MCCB is used for welding machines.
• Electric Feeders Protection: Due to its adjustable setting and high current handling, it is used in electric
feeders to distribute Power because it carries hundreds of amps that a normal MCB cannot handle.
• Generator Protection: They are also used for protection of large generator that generates hundreds of amps.
• Capacitor Bank Protection: Capacitor bank is used for power factor correction. MCCB is also used for its
protection against high currents.

44. Wires and Cables:
Wire: A wire is made of a single electrical conductor
 Domestic & small industry wiring applications
Cables: A cable is a group or bundle of multiple wires inside a common sheathing.
 Small and big industries Distribution and Transmission system
Wires
Cable
https://www.electricaltechnology.org/2020/04/types-wires-cables.html

45. Types of Wires:
There are mainly 5 types of wires:
1. Vulcanised Indian rubber wires(V.I.P)
2. Cab type sheathed wires(C.T.S)
3. Poly Vinyl Chloride wires(P.V.C)
4. Tough rubber sheath (T.R.S)
5. Flexible Wires

46. Vulcanised Indian rubber wires(V.I.R)

48. Cab type sheathed wires(C.T.S)

62. Electrical Safety precautions in handling electrical appliances:
 Switch off all plugs when not in use.
 Be careful while using a water heater.
Electric geysers should be switched off when not in use.
Oven and microwave should not be left running with out supervision.
Always handle electric appliances with dry hands.
Do not use a hair dryer in the bathroom.
Do not cut and make adjustments to electric cords.
Switch off all electric supply when on a vacation

63. Electric shock
An electric shock occurs when a
person comes into contact with an
electrical energy source. Electrical
energy flows through a portion of
the body causing a shock.
Exposure to electrical energy may
result in no injury at all or may
result in devastating damage or
death.

64. What are the causes of electric shock?
•Contact with a powerline or electrical arc flash
•Accidental contact with exposed electrical sources
•Faulty electrical wiring, installations and repairs
•Contact with metal, growing vegetation, or other conductive material exposed to electrical
current, such as a metal ladder that touches a powerline or other exposed wire
•Accidental contact with a downed power line, or with the earth near a downed powerline
•Shock from faulty or unprotected electrical products, such as household appliances (e.g., hair
dryers and toasters), power tools, medical devices, outlets, electrical plugs and extension cords
•Three-prong-to-two-prong grounded plug adapters
https://www.electrocuted.com/2019/09/11/electric-shock-what-is-it-causes-symptoms-treatments-safety/

66. Electric shock

67. First aid for electric shock
1. The first step is to separate the person from the source of electricity as quickly as
possible. The best way of doing this is to turn off the supply, for example, by
unplugging the appliance or by turning the mains off at the fusebox (consumer unit).
2. If this isn’t possible, then try to remove the source of electricity from the person using
a piece of insulating material, such as a length of wood.
3. NEVER touch the person receiving the electric shock, or you could suffer one too.
4. After removing the person from the source of electricity, if the person is
unconscious call for an ambulance immediately. Only those with the necessary
knowledge and skill should carry out first aid.

68. 5. Where the person is conscious and seems well, it is still advisable to monitor
their condition, as the effects of an electric shock may not be immediately
obvious. In worst case conditions, an electric shock may lead to a condition
known as electroporation, where cells within the body rupture, leading to tissue
death. Additional problems might include deep-seated burns, muscle damage
and broken bones.
6. Do CPR(Cardiopulmonary Resuscitation), if Necessary When you can safely touch the
person, do CPR if the person is not breathing or does not have a pulse.

70. Electrical Safety Rules:
1. Avoid contact with energized electrical circuits Please don’t make fun of this
rule if you already know this (and you probably already know if you are
reading these lines) and remember that if something bad occurs – you
probably won’t have second chance. That’s not funny.
2. Treat all electrical devices as if they are live or energize.Disconnect the
power source before servicing or repairing electrical equipment.
3. Use only tools and equipment with non-conducting handles when working on
electrical devices.

71. 4. Never use metallic pencils or rulers, or wear rings or metal watchbands
when working with electrical equipment. This rule is very easy to forget,
especially when you are showing some electrical part pointing with
metallic pencil
5. When it is necessary to handle equipment that is plugged in, be sure hands
are dry and, when possible, wear nonconductive gloves, protective clothes
and shoes with insulated soles.

72. 6. If it is safe to do so, work with only one hand, keeping the other hand at
your side or in your pocket, away from all conductive material. This
precaution reduces the likelihood of accidents that result in current passing
through the chest cavity.
7. If you ever read about current passing through human body you will know,
so remember – work with one hand only.
8. Minimize the use of electrical equipment in cold rooms or other areas
where condensation is likely. If equipment must be used in such areas,
mount the equipment on a wall or vertical panel

73. 9. If water or a chemical is spilled onto equipment, shut off power at the main switch
or circuit breaker and unplug the equipment.
Very Logical : NEVER try to remove water or similar from equipment while
energized. Afterall, it’s stupid to do so.
10. If an individual comes in contact with a live electrical conductor, do not touch
the equipment, cord or person. Disconnect the power source from the circuit breaker or
pull out the plug using a leather belt.
Tricky situation, and you must be very calm in order not to make the situation even
worse.
https://electrical-engineering-portal.com/21-safety-rules-for-working-with-electrical-equipment