Fire by short circuit: (im)possible?

I recently read in my local newspaper that a furniture showroom burned to the ground due to a short circuit. But then I thought about it and began to have my doubts. Because when there is a short circuit, the fuse or the fuse-box blows – whether or not it is fitted with earth protection - and the system goes dead. So the danger is averted. That’s what those protective devices are for.

Short circuit caused by halogen spots

But… if the customer has halogen spots, and those halogen spots were installed close to flammable materials such as wood or plastic, a fire is not inconceivable. And this often happens in shops. Those same halogen spots are only 12 volts so people think they are safe. But as shop fitters we know that at low voltages the current is quite high, so the wiring (if unjustly fitted) often overheats and causes a fire.

“Why doesn’t the fuse blow?”

You're probably wondering: “Why doesn’t that fuse or fuse-box blow automatically?” That’s because that same amateur also uses a lot of patch cables, and this increases the resistance (Ω) in the cables and socket connections. You can calculate the current by dividing the voltage (230 Volt) by the resistance (Ω).

Safety stipulations

But then it’s difficult to know how high the resistance is. Which is why the inspector uses special equipment to measure the systems in accordance with the NEN 1010 safety stipulations. And as an employer, you have a duty of care and you must use systems that are safe. That’s where NEN 3140 comes in, because it stipulates how electrical systems should be fitted.

Risk of fire

Back to that short circuit. Suppose the resistance is 3 Ω. Then 230 V divided by 3 Ω is 76.6 Ampere. That’s the current, and it’s not enough to blow a fuse or fuse-box. It takes a while and then the risk of fire increases. On the other hand, if the resistance is only 2 Ω, the current becomes so high that the fuse or fuse-box cuts out immediately and fire can be prevented. So you can see how important it is to have a professional electrical system: a difference of just 1 Ω can cause a serious problem. Regular visits by the inspector can prevent a lot of damage.


My conclusion: a fire caused by a short circuit is nonsense. What is not nonsense is that Alewijnse carries out inspections that significantly reduce the risk of fire. Contact your contact person for more information.

Sjaak Boks is a Technical Advisor at Alewijnse Delft B.V.


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