Where House Electrical Fires Actually Start

Electrical fires do not usually start in the middle of a cable. They start at connections, and they start because of heat that built up slowly at a joint that was not quite tight enough.

That one fact is worth more than a list of tips, because it tells you where to look and what is worth fixing.

Why connections and not cables

A cable is a known quantity. It has a rating, it is protected by a device sized for that rating, and if you overload it the device disconnects it.

A connection is different. A properly made termination has almost no resistance, so almost no heat. A slightly loose one has a little resistance, which makes a little heat. Heat makes metal expand and contract, and that cycling loosens the termination further, which adds resistance, which adds heat.

It is a fault that feeds itself, and it does it slowly, over months or years. It also draws normal current the whole time, so no protective device sees anything wrong. A circuit breaker protects the cable against too much current. It cannot see a hot joint carrying a normal current, and neither can an RCD. That blind spot is the whole problem.

Which is why "warm to the touch" is a symptom that matters so much more than it sounds.

The places it happens

The switchboard and meter box. The highest-energy terminations in the building are here, on the main switch and the incoming tails. This is also where heat has the most to work with. Browning around a fuse holder, discolouration on the enclosure, a smell of hot bakelite, or warmth on the cover are all worth acting on rather than noting.

On older boards there is an extra factor: aluminium tails creep under pressure, so a termination that was tight when it was made can loosen over the years.

Socket outlets, especially behind heavy loads. Heaters, kettles, dryers, air conditioners. A socket that is warm after running a heater, or that has browning at the pin slots, has a loose contact inside it. Double adaptors and older powerboards stacked with high-load appliances are the classic version of this.

Light fittings with the wrong lamp in them. Less common now that most lighting is LED, but a fitting rated for a low wattage with a halogen in it cooks its own terminations and the ceiling insulation around it.

Anywhere a connection has been extended or joined. Junctions in roof spaces, additions made during renovations, and joints made to reach a new position.

Downlights and insulation. Older halogen downlights need clearance. Where ceiling insulation has been installed or topped up later and pushed against them, the clearance is gone.

The outdoor half nobody checks

On the supply side there is a set of connections outdoors, in the weather, under mechanical load, that nobody looks at because they are above head height.

The point of attachment where an overhead service lands on the building carries the weight of the span, gets moved by every strong wind, and sits on the weather side. The service equipment and the meter enclosure sit in the sun and rain.

This is the stuff distributors issue defect notices about, and it is worth understanding that the notice is not bureaucracy. Those items are on the list because they are the ones that fail.

What actually reduces the risk

In rough order of how much difference each makes.

1. Act on heat and smell immediately. This is first because it is free and because it is the one signal protective devices cannot give you. Warm plate, warm cover, hot plastic smell, fishy smell: those are your only warning of the fault type that causes most electrical fires.

2. Have RCD protection, and test it. RCDs do not address hot joints, but they address the other major mechanism, which is current leaking to earth through damaged insulation or through a person. Press the test button every few months. It should trip instantly.

3. Get terminations checked when work is being done anyway. The main switch and the incoming terminations at your board are worth a check while the cover is off for something else. Thermal imaging under load will show a hot joint that looks fine to the eye, which is one of the more genuinely useful things fault finding equipment does.

4. Do not defeat protection. Fitting a larger fuse or breaker to stop nuisance tripping removes the cable's protection rather than fixing the cause. Repeatedly resetting a tripping device is the same decision made one reset at a time.

5. Stop using extension leads as permanent wiring. A lead run under a rug or behind furniture gets compressed, heats, and cannot lose that heat. If something needs power permanently, it needs a socket.

6. Deal with capacity rather than working around it. A house drawing more than its supply comfortably carries runs everything warmer, including the terminations. If your lights dim when the air conditioner starts, that is worth understanding properly.

7. Smoke alarms. Not electrical work, but the thing that determines the outcome rather than the probability. Interconnected alarms mean one going off in the roof is heard in the bedrooms.

What is mostly a myth

"Old wiring causes fires." Age on its own does not. Deteriorated insulation does, and old wiring is more likely to have it, especially pre-1960s VIR that has gone brittle at the board and in the roof. But a sound 1970s installation is not a fire risk for being from the 1970s. The condition is the thing, not the date.

"Turning things off at the wall prevents electrical fires." It reduces what is energised, which is not nothing. It does not address a hot termination on a circuit that is still live, and the board itself is always live.

"Surge protection prevents fires." Surge protection is for equipment, against transients. Different problem.

Frequently asked questions

How do I know if my switchboard is a risk? Heat, smell, discolouration and sound are the four signals. A board with no RCD protection is a different and separate risk, to people rather than to the building. If you want to read your own board, there is a guide to that.

Are ceramic fuses a fire risk? They are a slower form of protection than a modern breaker, and they depend on the right fuse wire being fitted, which is a real weakness. The bigger issue is usually what else is true of a board old enough to have them, including the backing panel and the condition of the tails.

Does an asbestos backing panel make a board more dangerous? Not electrically. It is an occupational risk during work, not a fire risk in service. Intact and undisturbed it is not doing anything. It changes the method and the cost of an upgrade.

Is a burning smell always electrical? No, and it is worth ruling out the obvious. But a hot plastic or fishy smell near a switchboard, a socket or a light fitting, with no other source, should be treated as electrical until somebody has looked.

Can you check the terminations at my board? Yes, and it is a sensible thing to combine with any other work. Where the incoming supply or the metering is involved, that part is Level 2 work.

If something here describes your place

Call 0485 824 714 and describe what you have noticed. If it is heat or a smell at the switchboard, say that first, because it changes how quickly we come.

We are accredited Level 2 ASPs under the NSW Government's ASP Scheme, authorised to work on the distribution network, with 15 years on connection-side work and a Lifetime Labour Warranty on what we do. Available 24 hours a day, free quotes, across Sydney and the Blue Mountains.

If you can see fire, smoke or arcing, call 000 first.