What Is an Earth-Leakage Circuit Breaker?

An earth-leakage circuit breaker (ELCB) is an electrical safety device designed to prevent electrical shock for installations with high earth impedance.

An ELCB’s job is to detect even small extraneous voltages that could occur on electrical equipment such as metal enclosures, and break the circuit to avoid damage or potential injury in such instances. Earth leakage indicates that the intended earthing protection of an electrical system is not functioning as designed, presenting an unsafe condition.

What is an Earth Leakage Circuit Breaker

There are two basic types of ELCBs, with distinct advantages and disadvantages.

2 Types of Earth-Leakage Circuit Breakers

ELCBs are categorized into two main classes:

1. Voltage Sensing Breakers

Voltage sensing ELCBs contain terminals that connect the line in/out, neutral in/out, earth, and fault. ELCBs contain a trip coil which senses voltage presence. In normal operation, there will be no voltage across the trip coil, allowing normal current flow.

When implementing ELCBs, an installation or building’s earth circuit includes connections to the breaker’s earth terminals, including the building’s circuit protective conductor (CPC). 

Should an earth fault occur, such as an instance where line voltage contacts the metal enclosure protected by the ELCB, voltage will in turn cross the trip coil, tripping the breaker and protecting the associated equipment and any humans who may come in contact with the electrical devices.

While many voltage sensing ELCBs are still in use today, they are typically not utilized in new construction, in part due to the disadvantage of these devices:

  • Any breaks in wiring connections to earth or live current source will generate a failure of the ELCB, rendering it useless. This could result in severe safety issues, including severe electric shock to humans.
  • Extra connections are required for connecting the source to the breaker.
  • Another device connected to the earthing system can generate external voltages that cause the breaker to trip.
  • Due to the nature of ELCB installations, where earthing systems are typically connected to such building components as metal pipes, these breakers do not facilitate easy splitting into multiple sections that retain independent protection from faults.

On the other hand, this type of ELCB has one advantage, in the fact that they are not as sensitive to fault conditions that generate nuisance trips of breakers. This is dependent on the environment of any particular installation, such as equipment downline from the ELCB.

2. Current Sensing Breakers

Current sensing breakers, also referred to as residual current devices (RCD) or residual current circuit breakers (RCCB), are the more commonly-used ELCBs today. They operate through incorporating a transformer with three windings – two primary and one secondary. The two primary windings support the line source and neutral wires. A wound coil is the secondary winding, and in normal conditions, is balanced to a zero voltage, since the line and neutral voltage offset each other.

When a fault takes place, voltage will route to the ground, creating an unbalanced condition. This generates current passing through the secondary, causing a trip of the breaker.

Advantages of RCCBs include:

  • Efficient and inexpensive
  • Fewer connections (phase and neutral only)

ELCBs in Practice

Main distinctions between ELCB and RCCB are:

  • RCCBs detect any earth fault, while ELCBs are designed to detect only earth faults generated through the main earth connection.
  • ELCBs are designed to work based on leakage of earth current, but RCCBs detect change in phase and neutral currents.

As with most electrical safety equipment, it is important to test every type of ELCB periodically, to make sure it is functioning normally to provide the intended protection. These are mechanical devices, and failures can occur.

Failing or questionable ELCBs should be replaced promptly to avoid unsafe conditions and potential damage to connected electrical equipment.

Finding the ELCBs You Need

There are many manufacturers of ELCBs of various types, including:

  • Major Tech
  • Fuji Electric
  • ABB
  • Siemens AG
  • Crabtree
  • Schneider Electric

When upgrading or replacing ELCBs, it’s important that the replacement is functionally equivalent and compatible with the unit(s) being replaced. Age of systems being upgraded can make this a significant challenge. 

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