Cajun's story about troubleshooting an overloaded breaker reminded me of something that happened on an offshore platform several years ago. It demonstrated the adage that "It is not possible to make anything foolproof because fools are so damn clever."
It was shortly after breakfast and the galley hand had just started some laundry. He left the laundry room and shortly after that there was a "BOOM" and a flash fire. Luckily, nobody was seriously injured although all the ceiling tiles in the mess hall were blown out and several things were singed. The washing machine was a total loss.
An investigation revealed that one of those clever fools had done a bit of Southern Engineering.
Offshore platforms are required to test their safety devices every month. Some of these are level switches that operate like your toilet tank valve. When the level gets too high, it trips a switch and sounds an alarm. In order to test them, the operator has to add water to the float tube until the switch activates. Looking for a way to make his job easier, this clever fool ran some tubing from a water connection on the quarters building over to the float tube. Now he only had to open a valve and he could adjust the level in the float tube at his whim.
What he didn't think about was that the top of the float tube was normally filled with natural gas. This gas worked its way back up the tubing and into the potable water piping of the quarters. It happened to accumulate in the piping to the laundry room. When the galley hand started the washing machine, the water valve on the washer opened and filled the washer with gas. Then it only took a small arc from the washer controls to cause an explosion.