Main Difference – Relay vs. Circuit Breaker
Relays and circuit breakers are devices used to stop currents flowing through circuits. The main difference between relay and circuit breaker is that a relay is typically used as a switch in circuits with small currents whereas a circuit breaker is used to sense and stop large currents from flowing in circuits.
What is a Relay
Relays act as switches in circuits involving small currents. Relays consist of electromagnets, which become energized when current flows around them. When the current becomes large enough, the electromagnet is able to pull one of the contacts in a circuit towards itself, breaking the circuit.
The video below explains how a relay works:
What is a Circuit Breaker
Circuit breakers are devices that turn a circuit off when it detects a large current. In doing so, circuit breakers A circuit breaker may use an electromagnet or a bimetal strip in order to break the circuit. Circuit breakers are commonly used in homes to ensure that a very large current does not flow through the wiring.
Often, the currents that a circuit breaker attempts to stop are so large that they can form an arc and jump from one side of an open switch to another. Some types of circuit breakers have the ability to sense the formation of arcs and to stop them from causing large currents in the circuit. In order to do this, a circuit breaker can increase the resistance of the conductors so that the current is forced to fall to zero. Another method that can be used in the case of alternating currents is to reduce the number of ions in the path of an arc just when the current falls to zero (in alternating currents, the current is momentarily zero just before it switches directions). When the current attempts to rise again, it is now unable to conduct through the gap.
A bimetal strip is a strip made by joining two strips of different metals. The two metals have two different expansivities, so at higher temperatures, differences in the lengths of the two metals become prominent. One metal is considerably lengthened than the other, which makes the structure to bend, as shown below:
A bimetal strip
The image below shows some circuit breakers used in domestic electric circuits:
Circuit breakers used in domestic circuits
The figure below shows the circuit symbols used to denote circuit breakers:
Symbols for indicating circuit breakers
Circuit breakers themselves make use of relays to detect large changes in current.
Difference Between Relay and Circuit Breaker
Purpose:
A relay is used to switch circuits with small currents.
Circuit breakers are typically used with large currents.
Components:
A relay typically uses an electromagnet.
Circuit breakers may use electromagnets, too, but they may also use a number of other mechanisms such as bimetal strips.
Function:
A relay can be used to divert current between two different circuits depending on the power supplied top the electromagnet.
A circuit breaker’s function is to stop the current flowing in a circuit altogether.
Preventing Arc:
A relay does not have the ability to prevent arcs.
Circuit breakers may have mechanisms to detect and stop the formation of arcs in the circuit.
Image Courtesy:
“Four 1 (single) pole circuit breakers fitted in a meter box.” by Bidgee (Own work) [CC BY-SA 3.0], via Wikimedia Commons
“Symbols for various types of breakers.” by Tara Zieminek (Using Adobe Illustrator, based on standard electrical symbols) [CC BY-SA 3.0], via Wikimedia Commons
