Did you know an electric shock from a current as small as 30mA can be fatal? Yes β 50mA to 100mA can cause immediate respiratory arrest. But 30mA is well above the "Let-Go" threshold. If your AC distribution system doesn't have the right RCD and fails to cut the power supply, the prolonged shock can cause breathing problems, ventricular fibrillation, and possibly death.
This is why we always insist on doing the electrical wiring of your adventure vehicle the right way. It's also why our government has enforced such strict policies around AC (alternating current) wiring. Even if you're using modern DIY-eligible plug-and-play AC wiring components, your setup must comply with the national standards for approval.
Some of these regulations specifically concern residual current devices (RCDs) for AC wiring. Choosing the right RCD for your van or motorhome is therefore not only about safety β it's also essential to ensure your setup passes the final CCEW inspection.
Residual Current Device vs Circuit Breaker: What's the Difference?
Circuit breakers and fuses are the most popular safety devices for protecting against electrical faults. However, they only protect circuits against excessive current, whether from overloading or short circuits.
If an electrical fault involves very small currents β such as 10mA or 30mA β both the circuit breaker and fuse will typically ignore it, as these values are well below their operating threshold. Yet these "insignificant" currents are still extremely dangerous and can cause fatal electrocution, electrical fires, or damage to equipment.
For this reason, the 240V AC distribution system in your caravan, campervan, RV, or motorhome must include an RCD.
An RCD (residual current device) is an electrical safety device that protects you and your property against residual currents (also known as leakage currents). These are electric currents that deviate from the normal circuit path (through the neutral line) and flow to ground or another unintended path.
Unlike circuit breakers, RCDs are designed to trip when they detect small leakage currents. This can be 10mA, 30mA, 50mA, 100mA, 300mA, or 500mA, depending on the unit.
What's Inside a Residual Current Device?
If we ignore the working principles, the internal structure of an RCD is somewhat similar to that of a circuit breaker:
- Toroid β A ferromagnetic ring at the centre, wound with live and neutral conductors in opposite directions.
- Live and neutral coils β These are the main coils wound on the toroid that carry the current through your circuit in the 240V AC distribution system.
- Search coil β This is a secondary coil wound around the toroid to "listen" to the magnetic imbalance between the live and neutral conductors.
- Tripping mechanism β This is the component that activates the RCD's safety trip. It is a highly sensitive, low-power electromechanical relay consisting of a trip coil connected to the search coil, a permanent magnet, a spring-loaded iron arm, and a mechanical latch.
- Test button mechanism β This is a push button integrated into a test circuit comprising a resistor and conductors connected between the live and neutral lines. When pressed, it simulates a leakage current, triggering the tripping mechanism.
- Main contacts β These are the conductive moving parts connected to the live and neutral sides of the RCD. They interrupt the electrical supply when the tripping mechanism is activated.
- Manual toggle switch β This is the switch that allows you to manually reset the RCD after it has tripped. It re-tensions the internal springs and pushes the iron arm back against the permanent magnet.
How Does an RCD Work?
The RCD works by electromagnetism β just like the mechanism in a circuit breaker that addresses short circuits.
In the event of an electrical fault, a magnetic imbalance occurs between the live and neutral conductors. This induces a small electrical current in the search coil.
The current from the search coil flows to the trip coil, which generates an electromagnetic field that cancels the permanent magnet's hold.
Once the permanent magnet loses its grip, the spring-loaded iron arm releases. The pre-tensioned spring then collapses, releasing the latch that holds the main contacts closed.
When the main contacts open, they cut off the power supply from your 240V AC distribution system before any serious damage can occur.
After fixing the issue that caused the RCD to trip, you use the manual handle to switch it back on. If it trips again immediately, the underlying issue has not yet been resolved.
How to Choose the Right RCD Safety Switch for Your Van
Having the right RCD in your van's AC distribution system is as important as having properly rated circuit breakers and fuses. Choose the wrong one, and you risk the very things you're trying to avoid β damaged equipment, electrical fires, or even electrocution.
Below are the key factors to consider when choosing the right residual current device(s) for your system.
Your AC distribution system
The very first thing to consider when buying a residual current device is the AC distribution system in your adventure vehicle. This includes your system's voltage, load current, wiring, and so on.
What type of leakage protection do you need?
Secondly, what type of residual currents do you want the RCD to protect against? This will help you decide whether you need a Type AC (for AC only), Type A (for AC and pulsating DC), or Type F (for AC, pulsating DC, and mixed frequencies).
How your distribution system is set up
The third step to consider when shopping for an RCD is how your AC distribution system is or will be wired. In most vans, you'll only have a single shore power distribution line. You only need to decide whether to use a traditional "fusebox" RCD, a socket RCD, or a portable version.
Traditional wiring vs plug-and-play
How is your AC distribution system wired? If you used traditional wiring, you'll need a traditional screw-terminal residual current device.
However, the new plug-and-play AC wiring system is the most convenient solution for caravans, campervans, and motorhomes. It is quick to install and replace on your own, and it also makes it easy to manage components like RCDs in the future.
Quick note: Here at Campervan Builders, we currently only stock RCDs for plug-and-play AC wiring. Some of the options include:
- 16A Plug and Play Inline RCD
- 15A External Shore Power Inlet with RCBO
- 16A Plug and Play RCBO with Earth Lead
- Plug and Play Inline RCD with 3 Pin Connector Lead
Maximum voltage rating
Different AC distribution systems have different voltage ratings. For example, while 230V is the standard AC voltage in Australia, some areas still use 240V. Therefore, your RCD should be rated for 230β240 VAC for maximum compatibility with shore power hook-ups across the country.
RCD or RCBO functionality?
What do you want your residual current device to do in the event of an electrical fault? A standard RCD only protects against residual currents. However, you can choose a modern RCBO (residual current breaker with overcurrent protection), which also offers protection against overload and short circuits.
Maximum load current rating
What is the maximum current your AC circuit will carry? The RCD you choose must be able to handle the total load current of your circuit. This is the high current rating (measured in amps) you see on the RCD unit, such as 32A, 50A, 63A, or higher.
Residual current rating
The main purpose of an RCD is to protect you and your property against residual currents (measured in milliamperes, mA). Therefore, you must ensure the device is sensitive enough to protect against the level of leakage current you're concerned about.
For instance, a 30mA RCD is the most common choice, as 30 milliamperes is the level at which leakage currents become potentially fatal to a healthy adult. However, there are also more sensitive options (such as 10mA) and less sensitive versions (such as 100mA or higher).
Manual trigger switch
As we mentioned earlier, the manual switch is a crucial part of an RCD. It allows you to reset the tripping arm and main contacts after an electrical fault. The switch can also be used to manually turn the power supply to the circuit off or on during maintenance. So, make sure the device you're buying has one.
Built-in test button
The test button (often labelled "T") is another crucial part of a residual current device. It allows you to test your RCD and verify that it works correctly β tripping appropriately in the event of an electrical leak.
Mechanical durability
Next, your new RCD must be well-made for optimal performance and durability, especially considering the extreme Australian off-grid conditions. We are not just talking about a heavy-duty housing but also mechanical durability (average number of operation cycles) and electrical durability (average number of electrical cycles).
Environmental protection and IP rating
Do you intend to install your RCD inside or outside your adventure vehicle? If you'll be mounting or using the device in an exposed area, ensure it has a good IP rating. For instance, many traditional RCDs can only be used indoors, whereas others have protection against dust and water β such as IP44, IP56, or IP66.
Compliance with Australian standards
Like we said in the beginning, Australia has some of the strictest regulations about everything β which is a good thing, as they are meant to protect us. As we already covered in our previous posts, these regulations are quite extensive when it comes to electrical wiring.
In our case, for instance, the electrical standard AS/NZS 3190 specifies that an RCD must not trip at 50% of its rated residual current; it must trip at 100% of its rated residual current. Meanwhile, AS/NZS 3760 requires a standard 30mA RCD to trip in less than 300ms, whereas a more sensitive 10mA RCD should trip within 40ms.
If an RCD fails these requirements, it is not only unsafe but also unsuitable for use. It will cause you to fail the mandatory inspection for the Certificate of Compliance for Electrical Work (CCEW).
How Often Should You Test Your RCD?
A residual current device (RCD) has a built-in test button, whereas a circuit breaker does not. This simply means that manufacturers place higher importance on the optimal performance of an RCD β after all, it is a life-safety device.
It also means that an RCD is not like a circuit breaker, which you only think about when it trips. You should test your RCD regularly to ensure it is functioning correctly.
If it were up to us, we would recommend testing your RCDs at least every month. While each test uses some of the "mechanical durability" we mentioned above, most RCDs are rated for 10,000β20,000 mechanical cycles. That means a monthly test will only use about 12 cycles per year β a very small fraction of even the 10,000-cycle limit.
Frequently Asked Questions
What does a residual current device do?
An RCD protects you and your property against residual (leakage) currents β electric currents that deviate from the normal circuit path and flow to ground or another unintended path. Unlike circuit breakers, RCDs trip when they detect small leakage currents, from 10mA up to 500mA depending on the unit.
What is the difference between an RCD and an RCBO?
A standard RCD only protects against residual currents. An RCBO (residual current breaker with overcurrent protection) also protects against overload and short circuits, combining two safety functions in one device.
What residual current rating should I choose for my caravan?
A 30mA RCD is the most common choice, as 30 milliamperes is the level at which leakage currents become potentially fatal to a healthy adult. More sensitive options (such as 10mA) and less sensitive versions (such as 100mA or higher) are also available.
How often should I test my caravan's RCD?
We recommend testing your RCDs at least every month. Most RCDs are rated for 10,000β20,000 mechanical cycles, so a monthly test only uses about 12 cycles per year β a very small fraction of even the 10,000-cycle limit.
Ready to wire your van's 240V system safely and pass your CCEW inspection? Browse our range of plug-and-play AC wiring components, including inline RCDs and RCBOs designed for caravans, campervans, and motorhomes.
