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What is an RCD and how does it work?

Updated: 7 days ago

Residual Current Devices (RCDs) are indispensable components in modern electrical systems, providing crucial protection against electric shocks and fires.

In this article, we'll delve into the world of RCDs, exploring their functionality, importance, and practical tips for ensuring their optimal performance in your workplace.

·       What is RCD?

·       Different types of RCDs

·       What does an RCD do?

·       How does an RCD work?

·       Importance of testing RCDs

·       Common problems with RCDs

·       Are RCDs reliable?

·       RCD testing and maintenance

What is a RCD and how does it works

What is RCD?

Residual Current Devices (RCDs) are safety switching devices, which designed to quickly disconnect electrical circuits when it detects an imbalance between the outgoing and incoming electrical currents.


Different types of RCDs

There are several different types of RCDs, each with specific functions and applications. Here are some common types:

1. Fixed RCDs: These RCDs are integrated within the consumer unit or fusebox of a building's electrical system. They offer protection for individual circuits or groups of circuits within the installation.

Fixed RCDs are commonly used in residential buildings, commercial establishments, and industrial facilities. They provide essential protection for various circuits, including lighting, power outlets, and specialised equipment. The primary and most common type of RCD to have for households is the fixed RCD installed inside your consumer unit (Fusebox).

2. Socket-outlet RCDs: These are special types of socket outlets that come with an integrated RCD. They replace standard socket outlets and provide dedicated protection for the user of the equipment plugged into them. They are typically used in areas where direct protection at the socket level is required.

Socket-outlet RCDs are often installed in locations where direct protection for users of electrical equipment is necessary. Common applications include kitchens, bathrooms, and workshops.

Portable RCDs
Portable RCDs

3. Portable RCDs (PRCDs): These RCDs are standalone devices that can be plugged into any standard socket outlet. Appliances or equipment can then be connected to the RCD, providing protection against electric shock for the user. Portable RCDs are useful in situations where fixed or socket-outlet RCDs are not available or practical, offering flexible and temporary protection.

Portable RCDs are frequently used in construction sites, outdoor events, DIY projects, and temporary installations. They offer flexibility and convenience, allowing users to ensure electrical safety wherever they are working, regardless of the availability of fixed protection measures.

Each type of RCD serves a specific purpose and is selected based on the requirements of the electrical installation and the level of protection needed.

What does an RCD do?

An RCD is a sensitive safety device that switches off electricity automatically if there is a fault. Their primary function is to detect any imbalance in the electric current flowing through a circuit, indicating the presence of a leakage to earth. By swiftly cutting off power supply, RCDs prevent potentially life-threatening electric shocks and mitigate the risk of electrical fires.


How does an RCD work?

At the core of an RCD lies a sensitive electromagnetic coil that continuously monitors the flow of electrical current. When the current flowing into the circuit differs from the returning current by a predetermined amount, indicating a leakage, the RCD triggers a rapid shutdown mechanism. This action ensures the safety of individuals and property by promptly isolating the faulty circuit.

Importance of testing RCDs

Regular testing and maintenance are critical to ensuring the reliability of RCDs. Routine inspections help identify any malfunctions or deterioration in performance, allowing for timely repairs or replacements.

Additionally, periodic testing ensures compliance with safety regulations and provides peace of mind knowing that your electrical system is adequately protected.


Common problems with RCDs

1. Minor Faults: RCDs may trip frequently due to minor faults such as appliance leakages, damaged wiring, or moisture ingress, causing inconvenience and disruption.

2. Low-quality RCDs: Some low-quality RCDs may be overly sensitive, leading to false trips even in the absence of actual faults.

3. Incorrect RCD Current Rating Used: Using RCDs with incorrect current ratings can result in inadequate protection or frequent tripping, compromising electrical safety and functionality.

4. Age and Wear: Over time, RCDs can deteriorate due to wear and aging components, reducing their effectiveness and necessitating replacement to maintain optimal performance.

5. Incorrect Installation: Improper installation of RCDs, such as incorrect wiring or inadequate testing, can lead to malfunctions or ineffective protection.

6. Lack of Regular Testing: Neglecting regular testing and maintenance of RCDs may result in undetected faults or malfunctions.

Are RCDs reliable?

RCDs are considered reliable and effective with providing around 97% reliability. When properly installed, maintained, and tested, RCDs can significantly reduce the risk of electric shock and electrical fires in homes, workplaces, and other settings.

RCD testing and maintenance

We recommend testing your RCD at least every six months to ensure it is operating correctly. Additionally, we offer Push Button Test and RCD Measurement services to assess the functionality and performance of your RCD.

NOTE: "Push button" and "RCD measurement" are terms commonly associated with testing and assessing the functionality of RCDs.

  • Push Button Test: This method tests the RCD by pressing a button on the device. Pressing the button simulates a fault, making the RCD trip and cut off power. It checks if the RCD is working and will react quickly in a real fault.


  • RCD Measurement: This process measures and assesses different aspects of an RCD to check how well it provides electrical safety. It includes testing how sensitive the RCD is in detecting small electrical leaks, how quickly it reacts to trip when there's a problem, and how reliable it is in various situations.


Both push button tests and RCD measurements are essential components of RCD maintenance and safety procedures. Regular testing and measurement help ensure that RCDs are functioning correctly and provide the necessary protection against electric shock and electrical hazards.


At TESTntel, safety is our top priority, regardless of the environment. Contact us today for a FREE QUOTE. Learn more about how TESTntel can help safeguard your environment against electrical hazards.

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