You go to change a light switch cover or unplug the heater, and there it is: a sticky, bright green substance oozing from the back of the fitting. It’s often called “green goo”, “green slime” or “cable greening”, and plenty of Kiwi homeowners have found it. It looks alarming, and while it isn’t a reason to panic, it is a sign your wiring is getting old.
Here’s what it is, why it happens, and what we do about it at Brady Electrical.
What is green goo?
PVC is the plastic used to insulate most household cable in New Zealand. Plasticisers are added to it to keep it flexible. In some older PVC formulations, the plasticiser wasn’t held firmly in the mix. Over decades, warmth from the current flowing through the cable draws the plasticiser out of the insulation and onto the copper conductor. There it dissolves tiny amounts of copper, and that’s what turns it green.
The liquid then creeps along the conductor, helped by capillary action and gravity. That’s why it tends to show up at the lowest point of a cable run, which is usually a fitting.
The UK’s Institution of Engineering and Technology (IET) says most cases came from cable made in the 1960s and 1970s, before PVC compounds were reformulated. Cases still turn up in newer cable now and then, though, especially where it has run hot.
Where you’ll see it
Green goo usually appears where cables end at a terminal, such as:
- Light switches, often at the bottom of a vertical drop from the ceiling
- Power points (sockets)
- Light fittings and ceiling roses
- Switchboards, around breaker and fuse terminals
It can look like a glossy green smear, sticky drips, or a crusty green deposit on the screws and terminals.
Is it dangerous?
The goo itself isn’t the main problem. What it tells you about your cable is.
- It means the insulation is drying out. As the plasticiser leaves, the PVC gradually gets harder and more brittle. Cable manufacturer Nexans notes that, over time, it can crack. Cracked insulation can lead to faults, shocks or overheating.
- It can conduct electricity. The IET notes that because the goo contains dissolved copper, it’s conductive and can encourage “tracking” (current leaking across surfaces) if left in a fitting.
- Don’t touch it with bare hands. The IET describes it as low toxicity, but it says it shouldn’t be handled without gloves. If you do touch it, wash your hands thoroughly. Keep kids and pets away from affected fittings.
- Heat speeds it up. Overloaded circuits, loose connections and warm spots like ceiling spaces all make the process faster.
Please don’t try to clean it out yourself. Wiping goo from the inside of a live fitting means working on electrical equipment. That’s a job for a licensed electrician. Cleaning it off also doesn’t fix the cable behind it.
Why it matters for older NZ homes
A lot of New Zealand houses, including many on the North Shore, were built or extended in the 1960s and 70s. Many still have some or all of their original wiring. These homes now often carry loads the original wiring was never designed for: heat pumps, induction cooktops, extra power points, and sometimes an EV charger. More load means more heat, and more heat means faster breakdown of tired insulation.
Green goo at one fitting is often a sign of how the rest of the circuit, or the house, is ageing. It’s worth getting it checked properly rather than covering it back up.
What an electrician does about it
When we’re called out to green goo, the usual process is:
- Visual inspection. We look at the affected fittings and others on the same circuit. We also check the switchboard and, where we can get to it, the cable in the ceiling and under the floor. We’re looking for brittle, cracked or discoloured insulation and for loose or overheated connections.
- Testing. We do insulation resistance testing to check how well the insulation is still doing its job, along with other standard safety tests on the circuit.
- Clean-up and making safe. For minor cases, we clean the affected fitting safely, replace damaged accessories and tighten or redo the terminations.
- Recommending a fix that fits the problem. That might be:
- Monitoring. If it’s isolated and the test results are good, we may recommend periodic re-inspection and testing.
- Partial rewire. We replace the affected circuit or cable runs.
- Full rewire. Where the original wiring is ageing throughout, this is often the most cost-effective long-term option. It usually goes together with a switchboard upgrade so you get modern RCD protection.
We’ll explain what we find in plain language and give you options. We won’t push a full rewire if it isn’t needed. All our work comes with our 12-month workmanship guarantee.
When to call an electrician
Get in touch if you notice:
- Green, sticky or oily residue at any switch, socket, light fitting or your switchboard
- Fittings that feel warm, buzz, or smell like hot plastic
- Flickering lights or breakers that trip often
- A home that still has its original 1960s–70s wiring and has never been inspected
If a fitting is hot, sparking or smells of burning, stop using it. If it’s safe to do so, turn off that circuit at the switchboard and call an electrician straight away.
FAQ
Can I just wipe the green goo away? Not inside a fitting. That means working on live electrical equipment, and cleaning it off doesn’t fix the ageing cable behind it. Leave it to a licensed electrician.
Does green goo mean my whole house needs rewiring? Not necessarily. Sometimes it’s limited to one circuit. Testing tells us how far it has spread, and we’ll recommend monitoring, a partial rewire or a full rewire based on what we find.
Is newer cable affected? Rarely. Modern PVC compounds are much more stable, but cable that runs hot for years can still be affected.
I touched it. Should I be worried? Wash your hands well with soap and water. It’s considered low toxicity, but avoid touching it again and keep it away from children and pets.
Spotted green goo? Let’s take a look
If you’ve found green goo in your home, or you’re not sure how old your wiring is, Brady Electrical can inspect and test it and give you honest advice. We cover the North Shore and the wider Auckland area.
Call 0210 265 4778, email info@bradyelectrical.co.nz, or contact us online to book an inspection.