Loud “popping” noise? Arcing?

[joshj88]

This evening my partner and I were sitting on the couch and heard a very loud sudden “pop”. It sounded like it came from the corner of our living room where there’s a single outlet. As the night went on we heard the same noise 2 more times which was loud and odd enough to put us on edge. After the last one we heard, there were 2 more quiet sounds that I wouldn’t say were “pop” noises comparing them to the louder ones. The outlet on the wall did not have anything plugged into it nor did it spark or smoke. So far, there hasn’t been humming or crackling. All 3 “pop’s” happened at random and were spread out a bit. Weather is getting colder where we are, although I’m not sure that would play a part. Everything I’ve read has suggested it to be an arc situation. Any ideas and advice on what it could be is appreciated.

 

[Lucien Nunes]

The main question is whether the sound was actually electrical in origin, and not perhaps some movement of part of the structure of the house. Obviously this can be hard to identify with just a couple of unexpected, sudden events.

In the electrical context there are two main kinds of arcing - 'parallel' where something short-circuits hot to ground or neutral and receives the full line voltage across the fault and often trips the breaker, and 'series' where a poor connection breaks contact while carrying current to a fixture, which does not trip a conventional breaker as there is no excess current, just excess heat due to the resistance. Note that although the outlet in the suspect area is not in use, it can still be carrying current to another fixture on the same circuit.

A loud sudden pop, if it is indeed an electrical event, is most likely to be a short-circuit, E.g. where rodent damage or a screw or nail through a cable has eventually led to the hot and ground conductors touching and forming a brief but intense arc. If no breakers tripped, this suggests that the fault 'blew clear' i.e. enough metal vapourised at the fault to remove the short-circuit and the conductors are a fraction of an inch apart, just enough to stop the current flow for now. You would tend to see at least a small flicker of the lights or brown-out of appliances, especially ones on the same circuit, due to the short-circuit momentarily reducing the voltage.

The alternative situation of a series arc is less likely, they tend to fizz, crackle and smoulder as there is no heavy fault current to trip the breaker or blow the fault clear, and you would likely see the affected circuit malfunctioning with appliances losing power or lights flickering.

This situation can sometimes be confirmed by an electrician using an insulation tester ('Megger') which can detect weakened or breached insulation. However the arc does not always leave a clear signature and sometimes it is necessary to visually inspect the cables. A visual inspection in the outlet and, if the box is in drywall, a look at the cables around it using a mirror through the hole, might be a useful first step.