Download Earth Leakage Circuit Breaker (ELCB)

By:
47.M.B.J.Varma
48.Mallikarjuna Abhilash
49.Maraka Kulateja
50.Prajakta Mategadikar
51.Medepalli Nikhil Raj
An Earth Leakage Circuit Breaker (ELCB) is a device used to directly
detect currents leaking to earth from an installation with high earth
impedance to prevent shock.
HISTORY
Voltage ELCBs were first introduced about sixty years ago and
current ELCB was first introduced about forty years ago.
For many years, the voltage operated ELCB and the differential
current operated ELCB were both referred to as ELCBs because
it was a simpler name to remember.
IEC decided to apply the term residual current device (RCD) to
differential-current-operated ELCBs.
Residual current refers to any current over and above the load
current.
ELCB Manufacturers:
Legrand
Havells
ABB (ASEA Brown Boveri)
Crabtree
Siemens AG
Schneider Electric
Vguard
 The main purpose of Earth leakage protectors is to prevent injury
to humans and animals due to electric shock.
 ELCBs were mainly used on TT earthing systems.
1. Voltage ELCB
2. Current ELCB
Voltage ELCB:
 One terminal of the relay coil is connected to the metal body of the
equipment to be protected against earth leakage and other terminal is
connected to the earth directly.
 If any insulation failure occurs or live phase wire touches the metal
body, of the equipment, there must be a voltage difference appears
across the terminal of the coil connected to the equipment body and
earth.
 This voltage difference produces a current to flow the relay coil.
 If the voltage difference crosses, a predetermined limit(gnerally 50V),
the current through the relay becomes sufficient to actuate the relay for
tripping the associated circuit breaker to disconnect the power supply
to the equipment
Voltage ELCB
Voltage ELCB
Advantages:
 Less sensitive to faulty conditions.
 Nuisance tripping especially during thunder storms(When an
installation has two connections to earth, a nearby high current
lightning strike will cause a voltage gradient in the soil, presenting the
ELCB sense coil with enough voltage to cause it to trip).
 If the installation’s earth rod is placed close to the earth rod of a
neighboring building, a high earth leakage current in the other
building can raise the local ground potential and cause a voltage
difference across the two earths, again tripping the ELCB.
Voltage ELCB
Disadvantages:
 They do not allow a single building system to be easily split into multiple
sections with independent fault protection, because earthing systems are
usually use common earth Rod.
• As electrically leaky appliances such as some water heaters, washing
machines and cookers may cause the ELCB to trip.
• They do not detect faults that don’t pass current through the CPC to the
earth rod.
What is the use of TEST button on ELCB?
The test facility provided on the home ELCB will only confirm the health of
the ELCB unit
That test facility does not confirm that the ELCB will trip when an electric shock
hazard does occur.
Current ELCB:
 Current-operated ELCBs are generally known as Residual-current devices
(RCD).
 These also protect against earth leakage.
 Both circuit conductors (supply and return) are run through a sensing coil;
any imbalance of the currents means the magnetic field does not perfectly
cancel. The device detects the imbalance and trips the contact.
 When the term ELCB is used it usually means a voltage-operated device.
 Similar devices that are current operated are called residual-current
devices.
 RCCB is more sensitive than ELCB.
Typical RCB circuit(Single Phase):
Current ELCB
Working:
 The polarity of the phase winding and neutral winding on the core is so
chosen that, in normal condition mmf of one winding opposes that of
another.
 As it is assumed that, in normal operating conditions the current goes
through the phase wire will be returned via neutral wire if there's no leakage
in between.
 As both currents are same, the resultant mmf produced by these two
currents is also zero-ideally.
 The relay coil is connected with another third winding wound on the CT
core as secondary. The terminals of this winding are connected to a relay
system.
Current ELCB
Working:
 In normal operating condition there would not be any current circulating in
the third winding as here is no flux in the core due to equal phase and
neutral current.
 When any earth leakage occurs in the equipment, there may be part of
phase current passes to the earth, through the leakage path instead of
returning via mental wire.
 Hence the magnitude of the neutral current passing through the RCCB is
not equal to phase current passing through it.
Typical RCB circuit(Three Phase):
This relay causes tripping of the associated circuit breaker to
disconnect the power supply to the equipment under protection
 Residual current circuit breaker is sometimes also referred as
residual current device (RCD) when we consider the device by
disassociating the circuit breaker attached to RCCB.
 The entire parts of RCCB except circuit breaker are referred as
RCD.
Sensitivity of RCB:
 Medium sensitivity (MS): 100- 300- 500- 1000 mA (for fire
protection)
 Low sensitivity (LS): 3- 10- 30 A (typically for protection of machine)
Break time of RCB:
 G (general use) for instantaneous RCDs (i.e. without a time delay)
Minimum break time: immediate
Maximum break time: 200 ms for 1x IΔn
S (selective) or T (time delayed) for RCDs with a short
time delay (typically used in circuits containing surge suppressors)
Minimum break time: 130 ms for 1x IΔn
Maximum break time: 500 ms for 1x IΔn
No JOLT From VOLT
Almost 12 people die due to electrocution every
day(Source-NCRB)
-42% of total fires occur due to electrical
sources(Source-OISD)
-8% deaths that occur in factories are due to
electricity.
-
At present to prevent electrical shock three wire system with
protective multiple earthing is used.
Installation of ELCB
ELCB needs effective earth to trip the power else require a
secondary path for current to unbalance in ELCB to operate
and protect.
ELCB should be tested once in a month for a better
protection.
Earth Loop Voltage Detector:
 Generally called as ELVD
 An intelligent sensor in the ELVD senses and compares the
voltage of the neutral and the earth terminals (Body) of the
appliance.
 If the voltage level or fault signal exceeds 75V, a positive
signal is sent to the circuit breaker to cut the power only to
the faulty appliance. All other lights and electrical appliances
in the home continue to function normally.
 All that needs to be done to restore power to the appliance is
to restart it after rectifying the fault in the appliance.
ELVD is far more better than conventional circuit breakers which
has delayed reaction presenting hazard.
The operating time of ELCB is <40 milliseconds where as of
ELVD is <10 milliseconds
Until the fault in the appliance has been fixed, the ELVD will not
allow the device to be powered.