Electrocution continues to be one of the main causes of fatalities at the workplace. In the US alone, workplace electrical incidents kill around 150 people every year and injure thousands more, according to Bureau of Labor Statistics data analysed by the Electrical Safety Foundation. A significant number of these deaths and injuries may be avoided with proper use of Residual Current Devices (RCDs).
What Are RCDs?
A Residual Current Device (RCD), also called Ground Fault Circuit Interrupter (GFCI), is a device that quickly breaks an electrical circuit to prevent serious harm from an ongoing electric shock. Injury may still occur, for example if a person falls after receiving a shock, or if the person touches both live and neutral conductors at the same time.
How Do They Work?
An electric current of around 30 mA through the human body could be enough to cause cardiac arrest or serious harm if it persists for more than a small fraction of a second. RCDs are designed to quickly and automatically disconnect a circuit ("trip") when they detect that the electric current is not balanced between the supply and return conductors of a circuit, that is, any leakage current, for example through an electric shock.
To be able to prevent heart defibrillation, an RCD that detects leakage of 30 mA should be able to trip within 25–40 milliseconds.
What Is the Difference Between RCDs and Circuit Breakers?
RCDs detect current leakage and break the circuit. By contrast, conventional circuit breakers or fuses only break the circuit when they detect overload (excessive current). For example, if the circuit breaker is rated for 13 A, it would only break the circuit if it detects an overcurrent or overload above 13 A. By the time it breaks the circuit, if it does at all, fatal injury may already have occurred.
In summary, you could say that RCDs protect people while circuit breakers and fuses protect equipment or electrical installations.
Are There RCDs That Also Protect Against Overcurrent?
Yes. They are called Residual Current Circuit Breakers (RCBOs). These are RCDs integrated with a Miniature Circuit Breaker (MCB). They break the circuit when they detect current leakage as well as when they detect overcurrent.
Sensitivity
RCDs have varying sensitivity depending on where they are fixed in a circuit. Those meant to protect people against direct-contact injury have higher sensitivity in the range of 10–30 mA. Others meant to protect against fire or equipment have lower sensitivity, in the range of 100 mA to 30 A. The tripping time also varies depending on the level of protection required. Please talk to an expert before purchasing and installing an RCD.
Where Are RCDs Installed?
RCDs come in many forms which are meant to be installed in various places. RCDs can be installed in:
- Consumer Power Distribution Units
- Wall sockets
- Plugs that fit into wall sockets
- Inline on electrical power cords (e.g. for equipment intended for use outside in wet areas)
Sources
- Electrical Safety Foundation International: Workplace Injury & Fatality Statistics
- ESFI: Workplace Electrical Fatalities 2011–2023 (BLS data)
Workplace safety is a critical factor for any grain handling business. Read our post on managing occupational safety alongside other key business factors like cash flow, inventory, and quality management.
