Extension cord safety comes down to a few rules. Use one lead of the right length, never plug cords or power boards into each other, unwind cord reels fully, keep cords out from under rugs, plug heaters and kettles straight into the wall, use an RCD outdoors, and replace any damaged lead.
WorkSafe's own line is simple: extension cords are for temporary use. Most of the trouble we see comes from leads and power boards that quietly became permanent, especially in older Auckland homes with only one or two sockets per room.
How much can an extension cord handle?
Most household extension cords, cord reels and power boards in New Zealand are rated at 10 amps. At 230 volts, that works out to roughly 2,300 watts in total, across everything plugged into it. Check the rating on the plug or label, because some cheaper or thinner leads are rated lower.
To put that in perspective:
- A fan heater can draw 2,000 to 2,400 watts on its own.
- A kettle is usually in the same range.
- A TV, phone charger or lamp draws a small fraction of that.
So a TV, a game console and a lamp on one power board is fine. A heater and a kettle sharing a power board is not. The appliance's power rating is on its label or in the manual.
The dos
- Pick the right lead for the job. Use a lead long enough to reach without strain, but not so long that metres of it are coiled up. Use a heavier lead for tools and outdoor gear.
- Unwind cord reels completely. A wound-up reel traps heat. Under heavy load the cable inside can get hot enough to melt its insulation. Many reels carry a lower rating when wound than unwound for exactly this reason.
- Look over leads before you use them. Check for cracked or split insulation, exposed coloured wires, loose plugs and scorch marks.
- Use an RCD outdoors. WorkSafe advises always using an RCD (or an isolating transformer) when an extension lead is used outside, so a damaged cord cannot give a fatal shock. If your outdoor socket is not RCD protected, use a portable RCD plug.
- Choose power boards with overload protection. Many have a reset button that trips if you plug in too much.
- Store leads loosely coiled in a dry place, away from sharp edges and heat.
The don'ts
- Don't daisy chain. Plugging one extension cord into another, or one power board into another, stacks up loose connections and makes overloading easy. If one lead will not reach, buy a longer one or get a socket installed.
- Don't run cords under rugs or carpet. Covered cords cannot shed heat, they get crushed underfoot, and you cannot see damage developing. Flat "under-rug" cords are sold for this, but we would still rather see a cord run along the skirting or a new socket put in where it is needed.
- Don't run heaters, kettles, washing machines or ovens off a multi-box. WorkSafe says these should be plugged directly into a wall socket.
- Don't run cords through doorways or windows where they get pinched when the door closes.
- Don't repair damaged leads with tape. WorkSafe is clear that taped cords should not be used.
- Don't use indoor leads outside in the wet, and keep plugs and connections off wet grass and out of puddles.
- Don't use a double adaptor on top of a power board. It is daisy chaining in a smaller package.
Signs an extension cord is overloaded or failing
Stop using the lead and unplug it if you notice:
- the plug, socket or cable feels warm or hot
- brown or black marks on the plug or power board
- a burning or hot plastic smell
- buzzing, crackling or sparks when you plug something in
- the power board's overload switch keeps tripping
- the wall socket the lead is plugged into feels warm
A warm wall socket points to a problem with the socket or the wiring behind it. That needs an electrician.
Extension cords and children
Leads and power boards on the floor are within easy reach of crawling babies and pets. Cover unused power board outlets, keep boards behind furniture and unplug cords that are not in use. Our guide to childproofing electrical outlets covers the details.
When an extension cord is the wrong answer
If you have power boards or leads that never move, the house is telling you it needs more sockets. Common examples:
- the lounge where the TV, internet modem and lamps all share one double socket
- the home office running a computer, monitors and a heater from one wall plate
- the garage or shed powered by a lead through the back door
- a bedroom with one socket on the wrong wall
Adding power points is usually a quick job. In older homes we often combine it with checking the existing circuits, because a house with too few sockets often also has ageing wiring. Our rewiring and additional power points service covers both, and we can advise on outdoor sockets with proper RCD protection at the same time. For the bigger picture of what else we do around the house, see our residential electrical services.
Can I repair my own extension lead?
New Zealand rules let owners repair their own appliances, cord sets and extension leads for private use, but only if the work follows the code of practice NZECP 50 and the lead is tested before it is used again. In practice most leads cost less to replace than to repair properly, so replacing a damaged one is the safer call.
Installing a new socket is different. That is fixed wiring, which in New Zealand is prescribed electrical work for licensed electricians. A limited owner-occupier exemption exists under the Electricity (Safety) Regulations 2010 (regulation 57), but new wiring under it must be checked and connected by a licensed inspector. For most people a licensed electrician is quicker and comes with a Certificate of Compliance.
When to call an electrician
- You rely on power boards or extension cords as permanent fixtures.
- A wall socket feels warm, looks scorched or has loose pins.
- You need power outdoors, in a garage or shed.
- Your RCD trips when you use a particular lead or tool outside.
Livewire's registered electricians install extra sockets and outdoor power across Auckland, from our base in Kumeū.
Frequently asked questions
Can you plug an extension cord into another extension cord?
You shouldn't. Daisy chaining adds extra connections that can loosen and overheat, and it makes it easy to overload the first lead in the chain. Use a single lead that is long enough, or have a socket installed closer.
Is it safe to leave an extension cord plugged in all the time?
A quality lead with light loads plugged in is not dangerous in itself, but extension cords are designed for temporary use. If a lead has become permanent, the safer fix is a new wall socket.
What should never be plugged into an extension cord?
Heaters, kettles, washing machines, dryers, ovens and other high-draw appliances. WorkSafe recommends plugging these directly into a wall socket.
Is it okay to run an extension cord under a rug?
No. A covered cord cannot get rid of heat, gets damaged by foot traffic, and hides warning signs like scorching. Run it along the wall instead, or get a socket installed where you need it.
Are extension cords a fire hazard?
They can be when they are overloaded, damaged, daisy chained, coiled up under load or covered by rugs and furniture. Used within their rating and checked regularly, they are fine for temporary jobs.
Do you have to fully unwind an extension lead?
Yes, especially a cord reel under heavy load. A wound reel traps heat and can overheat. Unwind it completely before plugging in anything substantial.
