Chat with us, powered by LiveChat
The Local Guys Logo
What Is An RCD?

What Is An RCD?

An residual-current device (RCD) also known as Ground Fault Circuit Interrupters (GFCIs) in some regions, device ensures our safety, also known as a residual-current circuit breaker (RCCB). An RCD is designed to swiftly interrupt an electrical circuit and stop the power supply in the event of an ongoing electric shock, minimising the risk of serious injury or other electrical hazards.

By detecting imbalances in the flow of electricity, it immediately disconnects the circuit, preventing further harm. It is important to note that an RCD may not provide protection in all circumstances.

Key Takeaways

  • A residual-current device (RCD) or residual-current circuit breaker (RCCB) is a device that quickly breaks an electrical circuit to prevent harm from an ongoing electric shock.
  • RCDs work by detecting any imbalance in the electric current between the supply and return conductors of a circuit, which indicates leakage current and presents a shock hazard.
  • RCDs are designed to disconnect the circuit quickly enough to prevent serious injury, as a current as low as 30 mA through the human body can cause cardiac arrest or harm if it persists.
  • RCDs are testable and resettable devices, with a test button to create a small leakage condition and a reset button to reconnect the conductors after a fault has been cleared.

Definition of an RCD

An RCD, also known as a residual-current device, is a safety device that quickly breaks an electrical circuit to prevent serious harm from electric shocks. It is designed to automatically disconnect a circuit when it detects an imbalance in the electric current between the supply and return conductors. This device is essential in providing protection against electric shocks and is commonly used in consumer units and power supplies.

RCDs are life-saving devices that can prevent injuries and even fatalities caused by electric shocks. They work by continuously comparing the current flow in both the active and neutral conductors of an electrical circuit. If the current becomes unbalanced, indicating leakage current, the RCD quickly disconnects the electricity supply. This rapid response ensures that any potential electric leak is detected and the power is cut off before it can cause serious harm.

It is important to note that while RCDs offer a high level of protection, they do not provide protection in all circumstances. For example, if a person contacts both the active and neutral conductors while handling faulty plugs or electrical equipment, the RCD will not trigger unless there is also a current flow to earth.

What is the Purpose of an RCD?

Test and tag rotorua

Test and tag Rotorua

The purpose of an RCD is to provide immediate protection against electric shocks by quickly disconnecting an electrical circuit when an imbalance in the electric current is detected. An RCD, also known as a residual current device, is a crucial electrical safety device that plays a vital role in circuit protection. It works by continuously comparing the current flow in both the active and neutral conductors of an electrical circuit. If the current flow becomes unbalanced, indicating a leakage of current to earth, the RCD will quickly disconnect the electrical supply. This fast response prevents electric shocks and reduces the risk of serious injury or damage.

RCDs are commonly used in power sockets and other electrical equipment to enhance electrical safety. They are designed to detect and respond to electrical faults, such as a person coming into contact with energised parts or faulty plugs. While RCDs significantly reduce the risk of electric shock, it is important to note that they may not provide protection in all circumstances. For example, an RCD may not trigger off the electricity supply if a person contacts both active and neutral conductors without a current flow to earth.

Functionality of an RCD

The functionality of an RCD lies in its ability to rapidly detect and respond to imbalances in electrical current, ensuring the immediate disconnection of the circuit to prevent electric shocks. An RCD is a protective device that is designed to monitor the flow of electric current in a circuit. It continuously compares the current flowing in the active (supply) and neutral (return) conductors of the circuit. If there is a difference in the currents, it indicates the presence of residual currents or leakage currents, which can pose a risk of electric shock.

When the RCD detects an imbalance, typically at a level of 30 milliamps or less, it quickly disconnects the electricity supply, thereby preventing any harm or damage. This is crucial for the safety of individuals using electrical appliances or working with power circuits.

In addition to its role in protecting against electrical shocks, an RCD also serves as a device for electrical testing. It can be tested using a test button, which simulates a leakage condition. If the RCD operates properly during the test, it can be trusted to perform its function effectively. It is important to regularly check RCDs to ensure that they are functioning correctly and providing the necessary protection.

RCD Testing Frequencies


RCD Testing Frequencies

3 Reasons Why RCD Testing is Crucial

Testing the RCD is of utmost importance for ensuring electrical safety and preventing potential hazards. Regular testing of the RCD switch is necessary to ensure its functionality and effectiveness in providing protection against electrical hazards.

  • Detection of Faulty RCD Devices: Testing the RCD helps identify any faults or malfunctions in the device. This ensures that it is functioning properly and can provide the necessary protection in case of electrical faults or current leakage.
  • Verification of Personal Protection: Testing the RCD ensures that it can detect and respond to current leakage in a timely manner. This provides additional protection for individuals using electrical appliances or power tools, minimising the risk of electric shock and potential injuries.
  • Compliance with Safety Standards: It demonstrates a commitment to ensuring electrical safety and prevents potential legal issues that may arise from non-compliance.Regular RCD testingis necessary to comply with safety standards and regulations.

Are RCDs Mandatory in NZ?

Yes, RCDs, essential for electrical safety, are mandated in many regions for diverse settings such as residences, commercial sites, and workplaces. Regulations governing their installation and upkeep vary per locale, with governments pivotal in enforcing compliance. Installation, typically by licensed electricians, must adhere to specified types and standards, considering factors like leakage current and circuit length.

Periodic testing ensures correct operation, with regulations dictating placement and maintenance protocols. RCDs guard against electrical fires, tripping swiftly in fault conditions, preventing shocks and fires. Compliance ensures protection against shock hazards, even in damp conditions, with particular focus on sensitive areas like kitchen sockets. These devices play a vital role in preventing needless tripping, safeguarding both people and property, with built-in test features ensuring continual effectiveness.

Role of RCDs in Preventing Electric Shock

RCDs play a vital role in preventing electric shock incidents by swiftly detecting and disconnecting electrical circuits when an imbalance in current flow is detected.

Three reasons why RCDs are essential in preventing electric shock accidents:

  • Swift detection: RCDs are designed to quickly detect any imbalance in current flow, such as when electricity is leaking to earth or when a person comes into contact with live parts of electrical devices. This swift detection allows the RCD to immediately disconnect the power supply, minimising the risk of electrocution.
  • Disconnecting electrical circuits: When an imbalance in current flow is detected, RCDs swiftly disconnect the electrical circuit. This action helps to protect individuals from the potentially harmful effects of electric shock, as it cuts off the flow of electricity to the affected area.
  • Peace of mind: By installing RCDs in residential circuits or power outlets, individuals can have peace of mind knowing that they have an extra layer of protection against electric shock accidents. RCDs provide an added level of safety by continuously monitoring the current flow and acting as a safety switch in case of any abnormalities.

It is important to choose an RCD with the appropriate current rating for the specific electrical devices and circuits it will be connected to. By doing so, individuals can ensure maximum safety and reduce the risk of electric shock accidents.

Limitations of RCDs

One limitation of RCDs is their inability to protect against electric shock incidents caused by direct contact with both active and neutral conductors. RCDs, also known as residual-current circuit breakers, are designed to quickly disconnect a circuit when there is a fault current or an imbalance in the current flow between the supply and return conductors.

They are effective in detecting leakage current and providing protection against electrical shocks caused by contact with energised parts or earth. However, in situations where a person comes into contact with both the active and neutral conductors simultaneously, an RCD may not be able to detect the fault and disconnect the circuit.

This limitation occurs because the RCD relies on the detection of a current imbalance between the active and neutral conductors to activate its protection mechanism. Therefore, it is important to note that while RCDs significantly reduce the risk of electric shock, they do not provide protection in all circumstances, especially when there is no current flow to earth. It is advisable to use additional safety measures, such as proper handling of faulty plugs and electrical equipment, to minimise the risk of electric shock incidents in such situations.

Choosing the Right RCD for Your Needs

What factors should be considered when selecting the appropriate RCD for your specific needs? Choosing the right RCD is essential to ensure the safety and efficiency of your electrical system. Here are three key factors to consider:


  • Contextually Relevant: Determine the specific requirements of your application. Consider the type of circuit or equipment that needs protection. For example, if you are dealing with sensitive electronic equipment, you may need an RCD with equipment leakage circuit interrupters (ELCI) to provide additional protection against small leakage currents.
  • Circuit Breaker Type: RCDs are available in different types, including residual current circuit breakers (RCCBs) and differential circuit breakers. RCCBs are generally used for residential and commercial applications, while differential circuit breakers are more suitable for industrial settings due to their higher breaking capacity.
  • Current Rating: Consider the maximum current that the RCD needs to handle. Ensure that the selected RCD has a current rating compatible with the electrical load it will be protecting. It is important to choose an RCD with the appropriate sensitivity to detect and respond to leakage currents effectively.

Frequently Asked Questions

What Are the Different Types of RCDs Available?

There are 6 different types of RCDs available, including double pole RCDs that disconnect both the energised and return conductors, and single pole RCDs that only disconnect the energised conductor. These devices are designed to prevent electric shock and ensure personal safety.

  • Socket-outlet RCDs
  • Fixed (or wired-in) RCDs
  • Portable RCDs
  • Combination RCDs (RCBOs – Residual Current Circuit Breaker with Overcurrent Protection)
  • Three-phase RCDs (used in industrial settings)
  • Time-delay RCDs (provide a delay before tripping)

How Often Should RCDs Be Tested?

The frequency of testing depends on local government regulations and workplace policies and environments. Testing involves pressing a to simulate a dangerous leakage and verifying that the RCD operates correctly. testing button

Regular testing of RCDs, including Socket-outlet RCDs, is crucial for safety. This testing involves simulating dangerous leakages by pressing a button and verifying RCD operation. It’s imperative to engage a qualified electrician for this assessment to mitigate risks, especially concerning faulty appliances or wiring, neutral current issues, and potential electrocution risks for those in contact.

This preventive measure is essential in safeguarding domestic circuits, connected appliances, and modern consumer units, minimising hazards associated with overcurrent and ordinary fuses within standard socket outlets or neutral wires.

Are There Any Specific Industries or Businesses That Are Required to Use RCDs?

There are specific industries and businesses that are required to use RCDs as part of their electrical safety measures. These include construction sites, manufacturing facilities, and any workplace where there is a risk of electric shock.

Can RCDs Protect Against All Types of Electrical Faults?

RCDs, or residual current devices, are designed to protect against electrical faults by quickly disconnecting a circuit when it detects an imbalance in electric current. While they significantly reduce the risk of electric shock, they may not provide protection in all circumstances.

Common electrical appliances that may trigger Residual Current Device (RCD) tripping include:

  1. Vacuum cleaners
  2. Hair dryers
  3. Washing machines
  4. Power tools
  5. Electric kettles
  6. Dishwashers
  7. Irons
  8. Toaster ovens
  9. Heaters (space heaters, electric blankets)
  10. Microwave ovens

These appliances can lead to RCD tripping due to electrical faults, water leaks, or circuit overloading. If you encounter frequent RCD tripping, it’s imperative to enlist a qualified electrician to examine your electrical setup and address any underlying issues.

Are There Any Additional Safety Measures That Should Be Taken Alongside Using RCDs?

Alongside the use of RCDs, several additional safety measures are advisable. These include incorporating Miniature Circuit Breakers for enhanced overcurrent protection and implementing Ground Fault Circuit Interrupters (GFCIs) or Socket RCDs to prevent electrocution risks, particularly for individuals in contact with electrical systems. Ensuring proper installation of Earth Leakage Protection helps mitigate unintended paths for current flow, especially in single circuits or individual socket circuits. Additionally, monitoring and addressing issues like faulty wiring, overload conditions, or nuisance tripping in lighting circuits are crucial safety practices, especially in commercial buildings. Vigilance in managing these elements alongside RCDs promotes a safer electrical environment, reducing potential hazards related to electrical systems and preventing risks of electrocution.

The Local Guys Test & Tag, experts in electrical safety, specialise in comprehensive electrical safety testing. Offering risk assessments for premises, advice on safety switches, electrical circuit safety, and conduct testing and tagging for portable appliances and equipment. Providing a free service quote, contact The Local Guys Test & Tag for further information.

Disclaimer: The information provided in this blog is for general informational purposes only. While we strive to ensure the accuracy and reliability of the information we strongly advise that any electrical work or modifications be carried out by a licensed and qualified professional electrician. The content of this blog should not be considered as a substitute for professional advice or consultation. Any reliance you place on such information is strictly at your own risk.
  • About the Author
  • Latest Posts
Jarrad Goulding

Jarrad has been working in the service industry for more than 10 years and has managed clients from very small hair dressers to national clients with sites all over Australia. Over the decade, Jarrad has proudly won and managed many large tenders with government bodies and commercial businesses nationally. Additionally, Jarrad has trained and supported many franchise partners over the years.

Related Articles