What Is an RCD and Why Does It Trip?

What Does an RCD Do?

An RCD (Residual Current Device) is a critical electrical safety component that helps protect people from electric shock and electrical fires. You’ll usually find RCDs in your switchboard, but they can also be built into certain power points or extension cords.

RCDs work by constantly monitoring the flow of electricity. If they detect a leak—like electricity escaping through water or even a person—they immediately shut off the power to prevent injury or property damage.

Why Is My RCD Tripping?

RCDs can trip for a range of reasons, but the most common is a faulty appliance. Outdoor fittings—like garden lights, sensors, or exterior power points—are also frequent causes, especially after heavy rain or water-blasting. Moisture can enter these fittings and create a leakage path to earth.

If your RCD has started tripping after bad weather, it’s likely doing its job by cutting off power to prevent a potential electric shock.

However, RCDs can also become faulty over time and start tripping unnecessarily. If you're not sure what's causing the issue, it’s best to call the team at Infinite Power and Lighting for a professional diagnosis and repair.

How to Troubleshoot a Tripping RCD

If the RCD Tripped When Using an Appliance:

It’s likely the appliance is faulty. Unplug it, then try resetting the RCD. If it stays on, you've found the problem.

If the RCD Tripped Without Obvious Cause:

1. Leave the RCD off.

2. Check all plugged-in appliances—unplug anything that isn’t working.

3. Reset the RCD.

If it stays on: Reconnect your appliances one at a time. If the RCD trips again, you've identified the faulty item.

If it trips immediately again: There could be a wiring or fitting issue. Contact us to investigate and safely restore power.

How Do RCDs Work?

RCDs monitor the current flowing in and out of a circuit. If any imbalance is detected—such as current leaking to earth through water or a person—it disconnects the power instantly, usually within milliseconds.

Common Questions About RCDs

Can an RCD Trip Without an Earth Wire? Yes. Even without an earth wire, current can leak through conductive materials, causing the RCD to trip.

Are RCDs the Same as Circuit Breakers? No. RCDs detect current leakage, while circuit breakers respond to overloads and short circuits. For full protection, both are needed—or you can use an RCBO, which combines both functions.

Do RCDs Trip From Overload? No. Overload protection comes from circuit breakers. RCDs only react to current leakage. That’s why combining them with MCBs or RCBOs is essential.

Are RCDs Required by Law in NZ?

Yes. In New Zealand, RCDs are legally required in new residential installations or when upgrades are done. Specialised RCDs are also mandatory in schools, childcare centres, and medical facilities. While not always required in commercial buildings, it’s good practice to have them installed on general-use outlets.

If you’re unsure whether your property meets safety standards, we offer RCD inspection and installation services across Auckland.

How to Test Your RCD

Press the “Test” button—this simulates a fault. The RCD should trip instantly. If it doesn’t, it may be faulty. It’s recommended to test your RCDs every six months.

For extra peace of mind, Infinite Power and Lighting offers ongoing maintenance services to keep your home or business compliant and safe.

Need Help With an RCD in Auckland?

If your RCD keeps tripping or you’re not sure if your system is properly protected, Infinite Power and Lighting Limited is here to help. We’re experienced electricians based in Auckland, offering RCD repairs, testing, and new installations.

🔌 Call us today on 021 104 8114💻 Or email us at admin@infinitepower.co.nz 🌐 Visit www.infinitepower.co.nz to learn more.

Let’s make sure your property is safe, compliant, and powered by experts you can trust.