Relay vs. Circuit Breaker vs. Isolator: Key Differences Explained

This article breaks down the differences between relays, circuit breakers, and isolators, three essential components in electrical systems. While they all play a role in controlling and protecting circuits, they operate under different principles and serve distinct purposes.

What is a Relay?

• A relay is an electrically controlled switch. It opens or closes contacts to control other devices within the same or a different electrical circuit.
• Relays are typically used in circuits with lower current capacity (maximum of 20A).
• They are generally smaller in size.
• Relays have at least two normally open (NO) or normally closed (NC) contacts.
• They are used in control circuits, automation circuits, protection circuits, and switching circuits.

What is a Circuit Breaker?

• A circuit breaker protects electrical circuits from damage resulting from overcurrent, usually due to a short circuit.
• It interrupts the flow of current when a fault is detected.
• Circuit breakers can be reset to normal operation after the fault is addressed, making them reusable, unlike fuses which are single-use.
• A circuit breaker can make or break a circuit under normal conditions, either manually or remotely.
• The main advantage of a circuit breaker is its ability to automatically break the circuit under faulty conditions.
• Examples include air blast circuit breakers, SF6 circuit breakers, and vacuum circuit breakers.

What is an Isolator?

• An isolator (or isolating switch) is used to disconnect a part of a system for maintenance or repairs.
• It can only open a circuit under no-load conditions.
• Because of this limitation, when two isolators are connected on either side of a circuit breaker, the isolators must be opened before the circuit breaker.
• After maintenance is complete, the isolators must be closed first, then the circuit breaker, to bring the system back online.

Circuit Breaker vs. Isolator: Key Differences

The following table highlights the key distinctions between circuit breakers and isolators: