ElectriPuzzles! (Version 1)
No prior knowledge of electricity or wiring is needed to solve these puzzles. All you need is the desire to try something new! There are three electrical puzzles below. The first one is easy, the second one is difficult, and the third one is extremely difficult.
GOOD LUCK!
Let's start with the basics. Circuit #1 is a very simple, common circuit used to switch on a lamp.
Now, let's talk about this circuit. There is a Power source. Power comes from the electrical outlets installed inside your walls. In a typical United States residence, they deliver 115 volts, with current alternating at a frequency of 60 hertz. If you touch this kind of electricity, you will at least feel an extremely painful shock and at worst die of electrocution. This particular type of switch is called a "single-pole, single throw" (SPST) switch because it has only one pole (the diagonal line touching the left-hand circle above the letter s in Switch) and one throw (the right-hand circle above the letter h in Switch). The switch shown above may either be open (lamp will be off) or closed (lamp will be on). It is for this reason that SPST switches have "on" and "off" labels. The voltage in the black wire is the one we are switching. The voltage in the white wire is connected directly to the lamp. Since a properly wired home has a "ground potential" equal to the voltage potential of the white wire, touching the white wire can't electrocute you if it has been wired properly. The electrical codes require that no switching be done on the white "neutral" wires unless simultaneous switching is done on the "hot" black wires. So, since no switching is done on the white wire, our circuit above meets code. Once last subtle point: the lamp is on only when it is connected across a Black wire and a White wire.
COOL FACTOID: Different countries have different electrical systems. For example, in South Africa the wall outlets deliver 220VAC at 50 Hz, the "neutral" wire is BLACK, all wall receptacles come equipped with a built-in disconnect switch, and the entire house is fed by a Ground-Fault-Circuit-Interrupter (GFCI) main circuit breaker! Weird, huh?
Puzzle # 1 (simple). Draw a circuit with one power source, 1 lamp, and 3 switches labeled Switch A, Switch B, and Switch C. Wire the circuit so that the lamp is on only when the following statement is true: Switch A is closed, and either Switch B or Switch C (or both) are also closed. Make sure your circuit "meets code".
Circuit #2 is slightly trickier.
Switches (a) and (b) are single-pole, double-throw switches, commonly known as "3-way switches", probably because it has three terminals. There is a grand total of 3 unique ways of wiring them together. The most common method is shown above. This circuit allows both switches to control the same lamp. As I've drawn it above, the lamp is on. If you operate either switch, the lamp will turn off. It is for this reason that 3-way switches can't have "on" and "off" labels. In other words, if the lamp is on and you flick one of the switches once, the lamp will shut off. If the lamp is off and you flick one of the switches once, the lamp will turn on. And since we're not switching the white wire, it meets code.
Circuit #3 shows an older, no longer used method of wiring 3-way switches.
I don't know how it got the name, but this configuration is known as the Carter System. Technically, it works, since flicking either switch turns the lamp from off to on or vice-versa. Why? Because the lamp will be on if it is connected across the black and white wires, and off if it's connected across black; black, or white; white. It works, but don't use it. Why not? Because it switches on the neutral white wire! Therefore it doesn't meet code.
Circuit #4 shows Circuit #2 with a few additions: we have two lamps instead of just one, and one power plug:
It may look a lot more complicated, but the only difference is that we are now turning on (or off) two lamps at the same time, and we have a plug that is always "hot" because it is connected across the black and white wires. This circuit is also very common. For instance, the left-hand side could be your home, and the right-hand side could be your garage in the back yard. The lamps both turn on to light up the entire back yard between the house and the garage. The plug must always be hot because your automatic garage-door opener is plugged into it. How many wires were required between the house and the garage? Count the number of horizontal wires crossed by the vertical dashed separator: FIVE (four blacks and one white).
You have now seen two unique ways (one legal, one not) of wiring 3-way switches. Yet there is, believe it or not, just one other unique way of wiring up a pair of 3-way switches. For an extra-hard challenge, try to figure it out right now without reading further. If you can't, the instructions in the next puzzle will give you a very mysterious clue to help you figure it out for yourself!
Puzzle # 2 (difficult). Rewire Circuit #4 so that it works the same way but only uses FOUR wires instead of FIVE. Ignore the ground wiring. Make sure your circuit "meets code". There is only one solution, and when you get it you'll have figured out the mysterious "third way" to hook up 3-way switches!
You may be wondering, what if I want to control the lamp from more than just two switches? Well, Circuit #5 answers that question.
Switch (c) is a double-pole, double-throw, polarity-reversing switch. It is commonly known as a 4-way switch. It can be in two different positions: criss-crossed as shown in solid, or straight-through as shown in dashes. Study it to convince yourself that flicking any one of the three switches will turn the lamp from off to on or vice-versa. You may have to draw it out several times, or erase and redraw the poles in different positions, until you see it actually does work. (solution at bottom)
Puzzle # 3 (extremely difficult). Add a 4-way switch to the solution of Puzzle #2.