How did the breaker get tripped when I dropped a box?

My house was built in the early 1900s and underwent a pretty major remodel in the 1970s. We bought the house in 2011. The breaker panel is on the new side, with a ground. Most of our outlets are still two-prong, although some are three-prong (I have yet to inspect them to see if they are properly grounded). I mention all this because I worry about the wiring, that the persons who worked on it didn't know what they were doing, and it is an upcoming task of mine to upgrade the 2-prong outlets to 3-prong....

Last night I was in my living room and dropped a box of toys. It landed on a corner and another corner hit the wall. The living room breaker tripped in the basement as a result. I don't believe this was a coincidence, because it was only in this room and we've never tripped this breaker before.

What tripped the breaker? My first thought was exposed wire in the wall, but could it have been a jostled junction box either in the wall (possible?) or under the floor? Is this something I need to take care of ASAP?

 

I think the vibration jostled something in the wall that's not supposed to be there, and shorted to something grounded or neutral.

 

Lets be clear. You are talking about a breaker not a switch aren't you?

 

Oops. Yes, a circuit breaker. I was struggling to find the right word. It looks like a switch.

 

Looks like a circuit breaker. Switches look like switches. Just kidding. You most likely have metal boxes in the wall, and very narrow ones at that. As Justin alluded to, one of the receptacles could have been just close enough for a hot wire to touch the wall of the box and bounce back to normal. That movement could have been enough to trip the breaker. I beleive if you remove the power to those receptacles close to the area where you dropped the box, and remove the cover plates to the receptacles, you will see a burned spot on the side nearest the black wire.

 

If you find the problem Larry is talking about you might want to wrap the device in a couple of layers of tape. While you don't normally do that or need to it would be a good precaution if you can identify the device.

 

While you have the power off and you're puling some receptacles out of their boxes, It would be a good time to make sure that all connections are made to the screw terminals and not to backstab holes.

Also, make sure all the terminal screws are tightened down, whether they have a wire under them or not. Receptacles often arrive with the screws backed out and ready for a wire to be looped around them. If all of the screws aren't run in before the receptacle is mounted in a metal box and energized, any backed-out screw on the black-wire side can be close enough to the box to make an arc likely.

 

I didn't realize this at the time, but on the base of the wall where the dropped toy box hit is one of those old four-prong phone outlets. I cringe to think that it made contact with electrical wiring. Ugh, this old house will be the death of me. Especially if there's an electrical fire.

 

Very unlikely. Usually that wiring is surface run along the base board.

 

Even if the old phone outlet is still energized, it is supplied with very different, lower potential power from a source that is derived from your electrical system in a remote location. Contacting, and even damaging, that outlet or its wiring should have no effect on your power system nor, for that matter, on your safety.

It isn't electrical wiring in the same sense that the wiring for your lights and receptacles is. As Ray said, "Very unlikely."