Fried Fuses Beware: Electrification Can Burn Your Mains Supply

Are Australian switchboards suitable for home electrification? Yes. Are some of them going to blow up as loads increase? Also yes.

Read on as we spell out a cautionary tale and some solid advice to minimise the risk of your lights going out.

What Happens To Overloaded Cables?

Generally speaking, power supplied to the average house from the grid comes via an underground conduit or overhead cable. At some point in the circuit there must be a fuse or circuit breaker to protect the wiring from any potential overload.

Whether you’ve gone for a spectacular result by driving a garden fork through the main supply cable, or tried the slow burn approach of charging two EVs and a roast meal, overloading a cable is dangerous. Excess current creates excess heat, which either melts cables quickly or fries them to a crisp.

If it goes on long enough, then insulation fails and things go exponentially pear shaped. Think of it like fireworks as a precursor to burning down your house.

Telltale discolouration and crumbling of the main supply cable shows the poor connection inside the service fuse holder has been overheating for some time.

Service Fuses Protect You And The Grid

I’ve seen firsthand when an overhead mains cable has been overloaded because the neighbour once rang me to ask if the lights in my house were flickering.

When I came out the front I witnessed two things: my petrified neighbour tearing off in his car, while the cable hanging from the power pole to the house was dripping plastic and throwing off increasingly large sparks.

The low voltage mains have an incredible capacity to deliver, and without a fuse in line, they’ll maintain an amazing show. Once you’ve melted or burnt off the insulation, the sparks melt the copper or aluminium conductor, like welding in reverse, and eventually it falls to the ground, throwing more sparks at it lands on and electrifies the chain mesh fence.

Once the exciting part had died down, I rang the network people and got them around to make things safe and fix everything up.

The white sheath has pulled back while the primary insulation is cooked, crumbling and exposing the wires. Corrosion on the copper conductor tells us this has been ongoing for some time, but either way this is EXPOSED LIVE PARTS ready to electrocute the unwary.

This Wouldn’t Happen Everywhere

There’s 17+ Distribution Network Service Providers (DNSPs) in Australia and they all have slightly differing rules about their connection to you the consumer.

Generally speaking the national electricity rules administered by the Australian Energy Regulator tell us that the service fuse is the demarcation between us and them.

Poles and wires upstream of the service fuse are owned and maintained by the DNSP.

 

Most things downstream of the service fuse are customer owned.

 

Where it gets tricky is that the retailers own the meter, however that piece of wire downstream of the service fuse, but upstream of the meter, it’s customer owned but also the responsibility of the DNSP.

I know this because I’ve asked the AER about whether I’m allowed to cut that wire and install a Fronius solar smart meter. Clutching their rosaries, the DNSP people exclaimed NO! but the AER said it would be easiest to bribe the retailer metering technician to install the meter I wanted, despite the DNSP objections.

What’s it got to do with you? Well in some instances, the service fuse is on the power pole or screwed to the fascia of your house.

For underground supplies, it might be hiding under a green pit cover in your front yard.

In these images, the service fuse is mounted inside the switchboard, typical of an older underground supply.

In any case, it might be worth keeping an eye out if you have an increasingly electric home.

The Story Goes

Thanks for this story must go to a regular contributor to our comments section on the blog. The images and the background explaining them lobbed in my inbox recently and I figured it’s well worth reporting:

Hi Anthony

 

We had a bit of an ‘oops’ solar-related thing happen yesterday which I’m told isn’t that uncommon (which in itself is also scary). I was charging the home batteries and EV in the middle of the day using a combination of grid and solar. Probably around the maximum load the single phase/63A house would normally allow (it was pretty cloudy). 

 

Then suddenly I could smell smoke. We found the source, the main service fuse to the property was smoking. You can see the charred cables going into and out of it. 

Don’t Panic

Charging an EV at a full 7kW, plus topping up your house battery and running the air conditioning could run a standard 63A single phase supply flat out. It’s rated for the job and will work reliably, provided all the connections are in good order.

What we’re seeing in these pictures isn’t ideal, but it’s more or less the system working as intended. Fuses and circuit breakers are basically the weak link, designed to fail when things go wrong. Obviously this particular mode of failure isn’t ideal but it’s not burning down houses every week.

After decades of service and thousands of heat cycles, a screwed connection can relax. Once it gets a little loose, and a little corrosion creeps in, things can go from good to bad to worse in pretty short order.

As EVs proliferate then this problem will become more common, mainly because charging an EV has little diversity. It’s full load, full time, so there’s no throttling like an air conditioner or cycling on and off like the simmerstat on a stove.

When you have a switchboard upgrade, or more importantly when the retailer gives you a new smart meter, it’s worth asking about the service fuse. When they change meters, the metering technician should at least tighten the screws on the service fuse.