what is the differance between over load relay and mcb?

Answer 1

When supplying a branch circuit with more than one live conductor, each live conductor must be protected by a breaker pole. To ensure that all live conductors are interrupted when any pole trips, a "common trip" breaker must be used. These may either contain two or three tripping mechanisms within one case, or for small breakers, may externally tie the poles together via their operating handles. Two pole common trip breakers are common on 120/240 volt systems where 240 volt loads (including major appliances or further distribution boards) span the two out-of-phase live wires. Three pole common trip breakers are typically used to supply three phase power to large motors or further distribution boards.

MCB (Miniature Circuit Breaker)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation.
The overload relay consists of a coil, a plunger, a dashpot, and a pair
of switch contacts. The plunger is attached to a disk suspended in an oil-filled chamber (dashpot). The coil connects in series with an associated 440-volt motor supply circuit and the switch contacts are in a 115-volt start-and-run circuit for the motor.

During normal operation, the magnetic flux induced by the coil is not great enough to cause an appreciable movement of the plunger. However, if an overload of sufficient magnitude and duration occurs, the increased current through the coil draws the plunger upward.

When the plunger and disk reach the end of their upward travel, the normally closed contacts open in the 115-volt start-and-run circuit, de-energizing the motor contactor which opens the 440-volt motor supply circuit. With the motor circuit open, the overload relay plunger drops and the relay resets.

Since the dashpot retards upward movement of the plunger disk, the circuit does not break instantaneously during an overload. Two conditions determine the delay time: (1) the size of the orifice in the plunger disk through which the oil must pass and (2) the magnitude of the overload (strength of the magnetic field).

Answer 2

MCB is miniature circuit breaker, it come is single pole, dobble pole, three pole and four pole ( 3 phase + 1 neutral)
Its main purpose is to protect the machine against any electrical fault like phase break or earthing or short corcuit

Overload relay is a relay that is used in the circuit besides the MCB to work upto a particular Ampere, if the motor draws more ampere than that adjusted, it will trip thus keeping the motor safe

Answer 3

An "overload relay" is a general term for any relay which is used to prevent current overload in a circuit. An "MCB relay" is a specific family of Minature Circuit Breakers which can be used as overload devices, typically in low current, A-C circuits.

Hope this helps!

Answer 4

Overload relays protect a motor by sensing the current going to the motor. Many of these use small heaters, often bi-metallic elements that bend when warmed by current to the motor. When current is too high for too long, heaters open the relay contacts carrying current to the coil of the contactor.
MCB means Miniature Circuit Breaker -- it is used for upto. 100Amps in the motor feeders. MCCB menas Moulded case Circuit Breaker -- it is used for. 25oAmps to 800Amps in the motor feeders. ELCB means Earth Leakage Circuit Breaker.
https://www.electrikals.com/products/rc-protection-devices/mcb?cnid=131&cid=689&page=1&pagesize=20

Answer 5

MCB is miniature circuit breaker which is thermal oprated and use for short circuit protection in small current
rating circuit.
In case of OLR over load relay, its only a primary device which senses only over loads.We need to connect contactor to break the circuit.

https://www.electrikals.com/

Answer 6

Both are similar in principle and function