This is a true story.
I was enjoying some much needed down time this August long weekend at the cottage, making breakfast for my family and enjoying a beautiful morning, when something caught my eye. I thought, did I just see a whisp of smoke? I didn't smell smoke and I'd lost sight of the whisp, so I brushed off the encounter. As I continued making breakfast, I saw it again - a whisp of smoke. This time I was sure what I saw, but as I was using the toaster at that moment I assumed my toast was burning and wasn't particularly concerned. I checked on the toast, and was surprised to find that the toast was just fine. Just then the smoke got thicker and I caught an odor of burning plastic, an odor I'm particularly sensitive to as a fire investigator. I immediately ran to the electrical panel and shut off the power to the building, noting that none of the breakers were tripped. As I sniffed and listened my way around the kitchen searching for the source of the smoke, I noticed a glossy sheen on the plug of the
toaster's power cord where it plugged into an electrical receptacle. I unplugged the toaster and found that my receptacle had a black eye!
I removed the receptacle from its outlet box and was surprised to find that the receptacle had more than just a black eye, it had been partially consumed by heat coming from the neutral line terminal screw. Whereas all of the other wires were tightly connected to the terminals of the receptacle, the neutral wire freely moved around its terminal screw.
I had managed to catch a high-resistance connection causing a fire in real time!
A high-resistance connection occurs when contact between a conductor and a terminal is poor, resulting in resistant flow of electricity through the connection. Resistance results in the production of heat; the greater
the resistance, the greater the heat. In my case, the neutral wire had come lose from its terminal at some point in time. There are several ways for a high-resistance connection to form: improper tightening of the terminal screw during installation; loosening of a terminal screw due to vibration; oxidation of the conductor or terminal caused by moisture; or material creep, which occurs when a material is under stress for a long period of time. In the case of my receptacle, I suspect that the terminal loosened due to creep. I was lucky. Although the receptacle was partially consumed, there was no damage to the outlet box or the wall.
I learned a valuable lesson that morning: just because something has been fine doesn't mean it will always be fine. I suppose as a forensic engineer I always knew this, but like most people, I take a lot of the dangers around me for granted, along with the safety mechanism in place that keep those dangers at bay. A high-resistance connection is a danger that doesn't really have a safety mechanism associated with it. There's nothing in a receptacle or a breaker panel to detect a high-resistance connection. Sure, if you have the tools and the know-how you can detect a high-resistance connection if you go looking for it, but most people would find the issue the same way I did - a fire occurs.
As is the case with all dangers, vigilance is the key to catching a high-resistance connection early. If you see plastic that is part of an electrical device start to change its colour or finish, take a closer look. Get familiar with the location of your electrical service equipment and the main circuit breaker (usually at the top of your breaker panel). If you see smoke and smell burning plastic, don't be afraid to turn off the power to the building and call Emergency Services. If you live in a house with an older electrical system, check out the electrical receptacles to make sure the connections are tight, or hire an electrical expert to assess the system for you.
I very was lucky to have been able to catch my high-resistance connection before it got out of control. I hate to think about what could have happened if I'd not been so lucky.
Stay safe everyone!