What do RCD’s do? A RCD (residual current device) is an electrical protective device, usually found within your switchboard. Sometimes you’ll find them built-in to a socket outlet or as part of an extension lead. RCD’s protect you against electric shock - and protect your property from fire - by automatically disconnecting the circuit when it detects current leakage.
Why is my RCD (Residual Current Device) tripping? There are many different causes for RCD tripping. The most likely cause of RCD tripping is a faulty appliance. Another common cause of RCD tripping is outdoor electrical fittings (sensors, lights, outdoor outlets etc). These fittings can become waterlogged, which will cause current leakage as water comes into contact with live parts within the fitting.
If your RCD has started tripping since you’ve done some water-blasting, or after heavy rain, then this is the likely cause. In such cases, the residual current device will trip to protect you from electric shock.
The RCD itself can also malfunction and start ‘nuisance’ tripping. If you’re unsure what fault is occurring, give us a call or an email. Our team will diagnose the issue and get your electricity restored quickly.
What can I do to fix it? If your RCD tripped after you turned something on (or plugged something in):
If your residual current device (RCD) trips after turning on or plugging in an appliance, it’s highly likely the appliance is faulty. Disconnect the appliance, then reset the RCD to see if it trips again.
If your RCD tripped randomly:
Leave the RCD off, then walk around your property and test all appliances that are plugged in. you can rule it out as the cause of the problem.
Unplug every device that is plugged in and won’t turn on.
Once you’ve done this, go back to the switchboard and switch back on the RCD.
If the RCD doesn’t trip: Give us a call to check if we can repair it.
If the RCD trips straight away:
Howdo RCDs (Residual Current Devices) work? An RCD detects electric shock by monitoring the balance between the live and neutral conductors. If a current imbalance occurs—such as when electricity flows through your body to the earth—the RCD detects this and rapidly disconnects the circuit, preventing harm.
What causes a RCD to trip? A RCD will trip when it detects a current imbalance in the live conductors of a circuit.
The connection to earth can be through conductive building materials, or worse – through you! (electric shock).
A RCD detects this fault and automatically disconnects power to the circuit, preventing property damage and physical harm.
How does a RCD prevent electric shock? If you come into contact with a live electrical conductor, current will flow from the point of connection - through your body - to the earth (electric shock).
As long as the shock current value is larger than 30mA (milliamps), the RCD is designed to detect it and automatically disconnect the supply, preventing further shock.
Why 30mA? because any shock current above 50mA can cause cardiac arrest (heart attack) in an adult human.
Why do both the lights and power turn off when the RCD trips? In New Zealand, it’s common for electricians to install a single RCD to protect multiple circuits—usually 2 power circuits and 1 lighting circuit. If an RCD trips on a power circuit, it may also affect lighting circuits. For greater protection, install one RCD per circuit.
Can an RCD trip with no earth conductor? Yes – even if your circuit cables don’t have an earth conductor, current can flow to earth through any conductive materials that the live conductors come into contact with.
Is an RCD the same as a circuit breaker? No – a residual current device (RCD) and a circuit breaker each have their own protective function. A RCD detects current imbalances, whereas a circuit breaker detects current overloads & short circuits. Both devices work by disconnecting the circuit when their respective faults are detected.
Will an RCD trip on overload? No – an RCD (or RCCB) will not trip if there is an overload on the active conductors, it only detects current imbalances.
RCBO’s are devices which combine both MCB (overload) and RCD (residual current) protection into one.
Is an RCD a legal requirement? Yes – in NZ, RCD’s are legally required to be installed on residential installations where new electrical work or additions have been carried out. There are a few exceptions to this rule, but in general it’s always a good idea to have them installed.
Schools, childcare centres and patient areas within medical facilities are required to have specific RCDs installed for a greater level of protection.
Get in touch with us if you’re unsure what level of protection you require for your installation.
Howdo I test if my RCD is working? Test your RCD by pressing the test button. It should trip, disconnecting the circuit. Regular testing every 6months ensures your residual current device is functioning correctly,keeping your home and business safe.
If you're looking for expert electricians in Auckland to help with repairs, get in touch with TCCO Electrical, your trusted provider for electrical services. We specialize in all aspects of electrical maintenance and repair, and we're here to help you with any RCD issues.
