Answer / sath

Normally MCB's are used for low voltage application.Phase
line is directly connected to the input pole of MCB.MCB's
are act as a contacter here.In normal operating condition
terminal of the MCB are closed position. if the current
value reach above the rated value then the conduct is open.
so there is no need for the relay here.

Answer / victorvgp

simply saying,

RELAY consists of coil wounded on core and a contactor
If you saw a construction of MCB, an arrangement similar to
relay is made with nc contact and an external switch.

During normal operation, current flows through MCB relay
coil is not sufficient to change the position of contactor,

But on faulty condition, the fault current flows through
the MCB relay coil is sufficient to change the position of
contactor as from nc to no.

r u got it.

Answer / sennapparajan

First question itself wrong.MCB contains small relay
mechanism and also a coil.when current flow through coil
beyong the limit the coil will act the mechanish and trips.

Answer / reddy

durgak sir, mcb means minature ckt breaker ok moulded case
ckt breaker means mccb

Answer / arun gur

MCB (minature ckt breaker)
contains a bymetalic strip which heats up and bend as
current flows through it. the mechanical switch is operated
after it bends above a perticular angle when current flows
beyond the rated current

Answer / j. r. gaikwad

Relay is name given to a mechanism which changes the
position of a switch under certain predetermined condition
e.g.excess load , excess current , under voltage , over
voltage etc.
MCB contains electromagnet operated switch to trip under
short circuit state ( as it operates insantaneously , this
is necessary under shortcircuit condition ) & a thermal
over load relay i.e. a switch operating because of bending
of a Bimetal strip at higher temp produced by the excess
heat produced by the excess current - due to over load .

MCB simply means "small" circuit breaker .It does contain
mechanism to trip , i.e. switch automatically under adverse
conditions !

This is the right answer.

Answer / durgak

MCB meance Moulded Circuit Breaker also called as miniature
circuit breaker which are small capacity ( low voltage )
breakers and these too are moulded. So MCB is a breaker but
moulded(sealed). The breaker is the term used to a unit
which breaks (opens) the circuit above its rated flow of
current. it has the characteristic and ability to self
operate and isolate(break) the circuit if there is a fault
down the line. Circuit breakers are used to connect the
LOAD to the power circuit(line). Once the breaker has
opened it can not get ON by itself. It is to be actuated
again.Thats why we find a certain breaking capacity value
in MCBs in Kilo Amps.For example for light/fan loads the
MCBs rating is 6Amps which have a breaking capacity of
9Kilo amps whereas power points for ACs need 15Amp MCBs
with breaking capacity of 9 t0 12 Kilo Amps.depends upon
the manufacturers specifications.
As on date best MCBs available in market are:-
MDS,L&T,Siemens. Others of second grade are:-
Havells,Standard,HPL,Indo-Asian.

Answer / maddy

I am studying the bimetallic strip used in MCB.
I am trying to theoretically calculate the temperature rise
of the strip when 1.13In (safe value of current for which
the MCB shouldnot trip) is passed through the bimetallic
strip. I am having the dimensions, resistivity, modulus of
elasticity, flexivity, density of the strip.
I even have the practical values with me for ever few
secons of current passed.
I tried to use the relation MC(dT)=I^2Rt
that is all the heat generated is used in the temperature
rise.
But practically other things need to be considered like
heat loss with environment, also the above formula holds
good for only few seconds and here the resistivity I have
taken constant will also vary.
Please help me out with a relevant solution.

Answer / uday

MCB means miniature circuit breaker .it operates on the
basis of relay action .it is provided with a coil connected
directly to the live wire.whenever the faulty current
occures which is greather than normal current thte coil get
energised and pulls the contact.in this manner fault is
isolated.

Answer / prahallad nayak

MCB contains metallic conductor, which expand during over
curren or voltage, so the nc becomes no, & the MCB operates.

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