Testing whether a power point is earthed correctly is an important safety check — a missing or faulty earth can cause electric shock or fire. In New Zealand, most electrical testing and remedial work is restricted and must be carried out by a licensed electrician, but there are a couple of simple checks a homeowner can safely perform without touching any wiring.
Why Earthing Matters
The earth (or protective earth) conductor provides a safe path for fault current to flow back to the switchboard and trip a breaker or fuse if something goes wrong — for example, if a live wire touches the metal casing of an appliance. Without a proper earth, that metal casing can become live and deliver a dangerous or fatal shock to anyone who touches it.
Under the New Zealand Building Code and wiring rules set out in AS/NZS 3000 (the Wiring Rules), all general-purpose power points in a home must be earthed. Older homes — particularly those wired before the 1970s — sometimes have two-wire systems with no earth conductor at all, which is a serious hazard.
What a Homeowner Can Safely Do
You are not permitted to open a power point, touch wiring, or use a multimeter in a way that involves probing live terminals — that is restricted electrical work under the Electrical Workers Registration Board (EWRB) rules. However, you can use a plug-in socket tester safely.
Using a Plug-In Socket Tester
A plug-in socket tester (sometimes called a mains tester or outlet tester) is a small device you simply plug into the power point. It has a row of indicator lights that show common wiring faults, including:
- Correct wiring (earth present and correctly connected)
- No earth (open earth)
- Live and neutral reversed
- Live and earth reversed (a dangerous fault)
- No live (open live)
These testers are widely available at Bunnings and Mitre 10 for a modest cost (as a rough guide, typically $20–$50). Look for one that suits NZ/Australian-style three-pin sockets (Type I).
How to use it:
- Make sure the power point switch is turned on.
- Plug the tester firmly into the socket.
- Read the indicator lights against the legend printed on the tester.
- If the tester shows no earth or any fault, do not use that power point and contact a licensed electrician.
Safety note: Even a plug-in tester cannot detect every fault. For example, it will not identify a high-resistance earth connection, a shared neutral, or certain wiring errors. A proper earth continuity and insulation resistance test requires calibrated equipment operated by a qualified professional.
What the Tester Cannot Tell You
A basic socket tester has real limitations:
| What it detects | What it misses |
|---|---|
| Open (missing) earth | High-resistance earth |
| Live/neutral reversal | Shared neutrals |
| Live/earth reversal | Deteriorated wiring insulation |
| No live supply | Intermittent faults |
For a thorough check — especially in an older home, after renovation work, or before purchasing a property — you need a licensed electrician to carry out a full Electrical Warrant of Fitness (EWoF) inspection or a periodic inspection and test using a calibrated multifunction installation tester.
Older Homes and Two-Wire Systems
If your home was built before roughly the mid-1970s, it may have been wired with only active and neutral conductors and no earth wire at all. In this case, a socket tester will show an open earth on every outlet. This is a significant safety issue and the wiring should be assessed and upgraded by a licensed electrician. BRANZ has useful guidance on older NZ housing and electrical systems.
RCDs (Residual Current Devices) and Earthing
Many modern NZ homes have RCDs (safety switches) installed at the switchboard. While an RCD provides excellent additional protection against electric shock, it does not replace the need for a proper earth. An RCD works by detecting imbalance between live and neutral current — but a correctly wired earth is still required for appliance safety and to ensure fault protection works as intended. Check MBIE Building Performance for current requirements around RCDs in NZ homes.
When to Call a Professional
You must call a licensed electrician if:
- Your socket tester shows any fault (no earth, reversed wiring, etc.)
- You have an older home with suspected two-wire wiring
- You want a thorough periodic inspection and test
- You are buying or selling a property and need electrical certification
- You want to install, replace, or move a power point — this is restricted electrical work and illegal to do yourself
- You are a landlord — the Healthy Homes Standards require rental properties to have safe electrical installations
All electrical installation and remedial work in NZ must be carried out by a registered electrician and certified with a Certificate of Compliance (CoC). You can find qualified local electricians on tradedirectory.co.nz.