Electrical safety is paramount for any home or business. Devices like RCDs (residual-current devices) and circuit breakers prevent fires, electrical equipment damage, and electrocution. However, these two protective devices work differently to detect faults and cut the electricity supply to circuits.
In this post, we’ll provide an overview of how RCDs and circuit breakers operate. We’ll discuss their key differences in detecting electrical issues and tripping power supply.
We’ll also compare their relative advantages and disadvantages and recommend when each type of device is most appropriate. Whether you’re an electrician or a homeowner, understanding the capabilities of RCDs versus circuit breakers will help you make informed decisions about electrical safety.
What are RCDs and How Do They Work?
An RCD, or residual-current device, is a specialised circuit breaker that monitors current flow in a circuit and rapidly disconnects the power if it detects even a small imbalance in the current. RCDs measure the current flowing out on the live/hot wire against the current returning on the neutral wire. Under normal conditions, these currents will be equal.
But if some of the current is leaking through to the earth or through a person who has suffered an electric shock, it will not return through the neutral wire. This causes a small discrepancy in current that the RCD is constantly monitoring for.
When the RCD detects a tiny difference of around 30 milliamps, it instantly triggers the safety switch to disconnect or trip the circuit. This quick disconnection prevents a lethal dose of current from continuing to flow through a person and minimises the risk of electrocution.
What are Circuit Breakers and How Do They Operate?
A circuit breaker is an automatic electrical switch that protects an electrical circuit from excess current. It aims to prevent overheating and damage to the wires and other hardware due to overloads or short circuits.
Circuit breakers contain a strip or wire made of two metals that expand and bend when heated. When too much current flows through the circuit, this strip heats up and bends until it triggers the mechanism inside the circuit breaker to trip the electrical switchboard and disconnect the power.
The amount of current required to trip a circuit breaker depends on its amp rating and is significantly higher than what would trigger an RCD. For example, a standard 15 amp circuit breaker may trip at 135% or 18 amps.
Circuit breakers are also designed to trip much slower than RCDs. It may take several seconds of overcurrent flowing for the circuit breaker metals to heat up and bend sufficiently to trip the switch. In contrast, RCDs take just a fraction of a second to disconnect power when even a small current imbalance is detected.
While circuit breakers prevent wires from overheating, they do not monitor for leakage currents and cannot protect against electric shocks. Their goal is primarily to prevent property damage, not injury.
Differences Between RCDs and Circuit Breakers
Continuous monitoring vs overcurrent detection
An RCD switch works by continuously measuring the current on the live and neutral wires to detect any imbalance indicating current leakage. This lets them quickly disconnect power at currents as low as 30mA to prevent electrocution.
Circuit breakers do not actively monitor for leakage currents. They are designed to trip only when high overcurrents flow through the short circuit, usually at least double the rated current. This protects the wiring from overheating damage but does not prevent electric shocks.
Prevent electrocution vs prevent fires/damage
The core function of RCDs is to prevent bodily harm from electric shocks. Even small leakages of current can be deadly, so RCDs trip rapidly to mitigate this risk.
Meanwhile, circuit breakers are mainly concerned with preventing property damage. They allow normal current flows and will only trip when overcurrents reach unsafe levels that could overheat wires or hardware. The circuit breaker will activate, cutting the power when it detects a high current fault, short circuit, or overload, such as when too many appliances are plugged into a single power point. Circuit breakers are crucial in protecting wiring systems and humans from electrical accidents. Their slower action is acceptable since no electrocution risk exists.
Speed of tripping
RCDs provide extraordinarily fast tripping speeds. Their electronic circuitry detects current imbalances and disconnects power points in as little as 0.03 seconds. This prevents prolonged electric shocks that could lead to death or serious burns.
In contrast, circuit breakers rely on mechanical heating and bending of a bimetal strip. This causes a slower trip time – up to several seconds for lower overloads. While fast enough to prevent fires, this lag is too slow to stop electrocutions.
RCDs usually require a manual reset button to be pushed to restore power after tripping. This ensures the electrical systems are checked before being re-energised. Some RCDs have auto-reset, but this is less common.
Circuit breakers automatically reset once the overload or short is removed, and the electrical current drops to normal. This allows power to resume without any manual intervention required.
Advantages and Disadvantages of RCDs and Circuit Breakers
Circuit breakers are the preferred method for preventing property damage from wiring overloads. Their automatic reset function maintains power after temporary high currents pass.
But circuit breakers are slower to trip and do not monitor for dangerous leakage currents. On the other hand, RCDs offer extremely fast-acting protection against an electrical shock, which makes them superior at preventing injury and saving lives.
However, RCDs are more expensive than circuit breakers and require resetting after tripping. Ultimately, RCDs are the best choice when safety is paramount, while circuit breakers provide an affordable form of overload protection. Using RCDs with appropriately sized circuit breakers balances safety and continuous operation for optimal electrical protection.
Which Should You Choose?
Understanding the main differences between an RCD and a circuit breaker empowers you to make smart decisions about electrical safety. While circuit breakers help prevent fires and equipment damage, RCDs are superior for detecting lethal leakage currents and preventing electrocution. Using both in a comprehensive protection plan ensures the safety and continuity of the electrical supply.
If you need help installing or testing RCDs and circuit breakers, contact Your Electrical Experts. Our licensed electricians can advise on the ideal combination of electrical safety devices for your unique needs. We stay up-to-date on the latest standards and installation best practices. For reliable and affordable electrical safety upgrades, call Your Electrical Experts today.
If you want to know more about these amazing devices, find out why RCD testing is important to keep your home safe!