DIFFERENCE BETWEEN RELAY, CIRCUIT BREAKER, & ISOLATOR

What is the difference between Relay,Circuit Breaker,Isolator?

Relay is a protective device which senses the faulty conditions in a power system line and initiates the operation of circuit breaker to isolate the faulty part from the rest of the healthy power system.Examples of relays are Over Current relay,Directional relay,etc..

Circuit Breaker is a device which can

• Make or break circuit under normal conditions either manually or through remote control.
• Break circuit automatically under faulty conditions.
• Make or break circuit under faulty conditions either manually or through remote control.

Some types of circuit breakers are Air blast circuit breakers,Vaccum Circuit Breakers ,SF6 Circuit Breakers,etc.You can notice the circuit breakers near to the transformers.Next time when you see a transformer search for the circuit breaker.Mostly it will be SF6 Circuit Breakers.

Isolator or Isolating Switch is a device which is used to disconnect a part of the system for maintanance purpose and repairs.Isolator can open a circuit under no load condition only.If two isolators are connected on either sides of circuit breaker,then the circuit breaker must be opened before opening the isolators.

After perfoming maitanancee work on the circuit breaker,isolators must be closed first and then the circuit breaker must be closed to bring the system into operation.

RESISTANCE COLOUR CODE FOR RESISTORS

In many interviews for the Electrical Engineers (FRESHERS),they will give you a resistor in your hand ask you to tell the resistance value by seeing the colour codes on the resistor.In basic Electrical workshop, the first thing you learnt would be "How to identify the resistance value using colour code for the resistor ?".The way to remember the colour code is BB ROY of Great Britain has Very Good Wife.

Usually the resistors would be having 4-band code.Starting from the left the first 2 bands are the significant figure of the resistance value.The Third band is the decimal multiplier.There will be a much bigger gap between the third and fourth band.The fourth band indicates the tolerance value.Usually the colour code for tolerance is either Gold or Silver.

Gold indicates 5% tolerance level,Silver indicates 10% tolerance level and no fourth band indicates 20% tolerance level.Some resistors have five band colour.In that case first three bands are significant figures of the resistance value,fourth band is the decimal multiplier,fifth band is the tolerance level.

B    - Black

B(ROY)    - Brown
R    - Red
O    - Orange
Y    - Yellow
G(reat)    - Green
Britain    - Blue
Very    - Violet
Good    - Grey
Wife    - White