what causes multi-boxes to overheat/cause fires


How do multi boxes cause fires? Should the circuit breaker trip before it can overheat?

In: 0

It is a human problem. When there are lots of multi boxes (sometimes connected together), people tend to forget how many and how large the devices are that connect to that multi outlet.

A circuit breaker will usually trip of there is a short circuit or massive overcurrent. But the problem is the circuit breaker limit might be high enough not to trip but the current is enough to overheat the outlet boxes and wires (a good multiple outlet should be fused).

The more wires that run all over the place, the higher the chance of damaging some parts of the wire and that wire happens to run close to furniture/curtains that may be flammable. In a short circuit, the temperature builds up very quickly – even if the breaker trips, temperatures might well be high enough to ignite stuff.

The problem is that people aren’t careful enough.

I assume you’re talking about extension sockets/leads?

In theory yeah the breaker will trip first in a perfect world. In reality the breaker assumes it’s supplying a single cable, and it doesn’t trip instantly. Two cables sitting next to each other heat up a little bit more than just one. Three or four heat up even more.

Add in that extra extensions cause more volt drop, which can result in end devices drawing more current to compensate.

In the UK it’s pretty normal for the breaker to be rated at 16A or 20A. Several sockets spread throughout the house are on one breaker, and each socket is expected to only take up to 13A max as the end devices are designed for that. But if you’re not a thoughtful user and stick in some extensions suddenly you can very easily exceed the 13A on a single socket, which is bad for that socket but so long as it’s under 16A the breaker won’t necessarily care about it.

There’s nothing wrong with using extension cables or additional sockets. You just need to be thoughtful of what’s being plugged in to it, how long they’re running and how well ventilated (or not) the overall install is.