The Unit#1 tenant complained that their 3-way switches for the staircase light sometimes work and sometimes don’t. At first I thought it got to be the bad light bulb or poor wiring due to aging. So last week I went there and checked the light bulb and re-connected the wires by cutting out the old segments of the wires and re-stripping and re-connecting the wires. I also noticed the wires were inserted into the slots on the switch instead of forming a loop around the screws in the side the switches. I then found out the poor job that the tenant or her friend had done to fix the problem, resulting in poor connection. After re-connecting the wires to the switch the right way, I figured the problem had been fixed.
Not so, she claimed. The “intermittent” problem still persisted. I then went back and checked that there is no intermittent problem. Instead, the problem was that when the switch upstairs is in the “off” state (as far as the light is concerned) the switch downstairs cannot turn on the light. And yet it’s OK the other way around. After studying the 3-way switch on Google search, I refreshed my memory of the principle of the 3-way switch before I went to the apartment. This Youtube video was particularly informative.
After arriving at the apartment and studying the wires from the switch, I was able to figure out that the wire connection was the switch-switch-light configuration. I then sketched on my hand of what has been installed vs. what the way it should be. The solution was quite obvious that my tenant has reversed the position of the wires between the common hot-wire to the light and the hot-wire from the downstairs switch, resulting in this particular problem. Upon reversing the positions, the switch are now working just fine. Thanks to the power of the Internet, even an electronic engineer can handle the most difficult household electrical problem. 🙂