After seeing the shocking footage of the fire at the Notre Dame Cathedral in Paris, people were quick to jump to conclusions about the start of the blaze, many claiming without evidence that it was an act of arson or terrorism. A full investigation is planned, but officials are saying it was likely caused by a simple electrical short circuit.
But this has lead to some questions on how exactly a short circuit can cause a fire. While the details haven’t been figured out just yet, there are a couple of ways this could happen.
But first, short circuits. There’s an equation called “Ohm’s Law” that relates voltage, resistance, and current. With a specific voltage and no resistance, it means there’s a lot of current. This can manifest itself as a spark as the circuit is being joined or as heat, like when you connect two ends of a battery with paperclip or use a toaster.
What could have happened? If it’s construction related, a wire likely got damaged by something hitting it or pinching it. It could even be something unexpected like a rodent chewing a wire. In essence, the belief right now is that something connected two wires that weren’t supposed to be connected, causing them to either spark or heat up to an ignition temperature.
What protective measures are there? Modern safety requires or recommends a lot of different items, it can be overwhelming at times. Two big items that could have been involved are circuit breakers or Ground Fault Circuit Interrupters, GFCIs, which are also known as “Residual Current Devices” or RCDs. Circuit breakers detect when too much current is being pulled and trip when that’s the case, they’ve mostly replaced fuses in modern houses. GFCIs, however, are testing for an imbalance between what goes out and what goes in. They both have their faults - circuit breakers sometimes don’t trip when they’re supposed to, or, it could be an imperfect short circuit that is pulling too much current but not enough to exceed the limit of the circuit breaker. GFCIs are usually much more sensitive, but if the short circuit is with the return loop, it’s possible, though quite unlikely, that it won’t be detected. Much more likely, in my opinion, is that GFCIs weren’t used. They’re annoying to use because if you switch on a big load, like a saw, it will trip when it’s not supposed to, so I personally avoid them when using heavier equipment. It’s likely that there wasn’t a GFCI on the circuit but there could’ve been a circuit breaker installed and it simply wasn’t effective at stopping the problem.
Also, supply voltage in France is 230 volts, which is the same as places such as India, the rest of Europe and many places in South America. But compared to places such as the United States, Canada, and Japan, that’s about double the voltage we’re used to. Could that have contributed to the fire? In one way, possibly. A larger voltage means that the arcing of a short could be bigger, in other words, it could create a bigger spark, making it more likely to cause a fire. If it is a short where the safety circuits haven’t tripped and a wire just got hotter and hotter, like on your toaster, then the voltage doesn’t really make a difference because it’s a matter of power, a combination of both voltage and current. For example, 110 volts at 10 amps is the same amount of power as 220 volts at 5 amps. The grid effectively provides the same amount of power, no matter the voltage, so that wouldn’t have made a difference.
We don’t know what happened yet, and this is all conjecture based on the limited information we have. But, if it was a short circuit, it was likely that there was either no circuit protection or faulty circuit protection, and an external factor exposed and shorted the wires, causing them to either spark of heat up.
In the US, from 2014 to 2016, there were over 100,000 non-residential fires reported, of which, approximately 8% were attributed to electrical malfunction. The use of GFCIs, as well as regularly testing them and testing the circuit breakers in our homes and businesses can help drop this number. Importantly, if you’re working with electricity in your home and don’t know what you’re doing, reach out to a licensed electrician. Nobody is perfect and we can never eliminate all risks, but they’re trained and legally qualified to help reduce the chance of a catastrophic failure.
