I'm about to install several Hunter ceiling fans. The instructions that came with the fan show three wires coming from the ceiling box for a single switch light. When I remove the light, there are only two wires leading to it. And the wires are old, cloth covered. (House was built in '50.) Why two rather than three and what the heck do I do now?
Two is "normal". Black for hot and white for neutral.
Your fan has 3 wires (4 counting the green ground). You will have a white which you will connect to your neutral and you will have power for light and power for fan. Both of the power lines will be capped with your "black"/hot wire coming in.
To have the light and fan controlled independently you would need to rewire from fan to switch with 12-3 (or 14-3). An alternative is to install a remote that has sensor sitting in fan unit (or buy a fan with it built in).
The 3 wires are normally hot, neutral, and ground. It sounds like your home doesn't have a ground wire.
Equipment earthing conductors provide an electrical connection between non-current-carrying metallic parts of equipment and the earth. The reason for doing this according to the U.S. National Electrical Code (NEC), is to limit the voltage imposed by lightning, line surges, and contact with higher voltage lines. The equipment earthing conductor is usually also used as the equipment bonding conductor (see below).
Equipment bonding conductors provide a low impedance path between non-current-carrying metallic parts of equipment and one of the conductors of that electrical system's source, so that if a part becomes energized for any reason, such as a frayed or damaged conductor, a short circuit will occur and operate a circuit breaker or fuse to disconnect the faulted circuit. By bonding (interconnecting) all exposed non-current carrying metal objects together, they should remain near the same potential thus reducing the chance of a shock. This is especially important in bathrooms where one may be in contact with several different metallic systems such as supply and drain pipes and appliance frames. The equipment bonding conductor is usually also used as the equipment earthing conductor (see above).
If the box is metallic, there's a chance it may still be grounded, even though there is no wire. There's an answer to a similar question that describes how to check if a box is grounded.
If the box is grounded..
If the box is grounded, then you can connect the ground wire from the fan directly to the box, and the fan will be grounded.
If the box is not grounded, you have two choices:
- Run a ground to the box. This would mean running a new wire back to the panel (could be bare copper, but if you're doing the work may be better just to run a new wire - 14/3 would be the best), which could mean opening up drywall.
- Wire the fan without ground. This is slightly dangerous, but not moreso than the when the previous fixture was there -- except that people do touch fans to control them. If something ever happens to cause the fixture to become energized (eg a frayed wire inside), someone who touches it will likely be shocked (which can cause serious injuries and even death).
Personally, if I was unable to get a ground to the box, I'd probably use a fan that was remote controlled so no one ever has a need to touch it (get a fan either with no pull strings/controls, or cut the cords off so no one is tempted to touch them). The wall switch can be left in to control overall power, and the remote used to switch light/fan speed, or the wall switch can be removed so the power is permanently on and the remote is used for everything.
In any case, you should connect the fan's ground wire to the box, so that at least the fan body and box are bonded (at the same electrical potential).
DO NOT CONNECT GROUND AND NEUTRAL in the box. This is sometimes called a "bootleg ground" and is not only pointless, but actually very dangerous. If the neutral wire ever has a fault ANYWHERE, in addition to the fixture simply not working, it becomes energized and you can be shocked if you touch it (as you likely would to, say, check if the light bulb was burnt out).
Your wiring is an ungrounded system, possibly what was called "knob and tube", which refers to the ceramic insulators used. Be very careful with the cloth-covered insulation, as age will make it quite brittle and easily damaged. Most of the times with wiring this old, both appear the same color, making your install more time-consuming determining hot from neutral. I have used heat-shrink tubing in the past to ensure the old cloth insulation remained intact during fixture replacement, as well as for color coding the existing wires. You only have to sleeve it over the existing wire, no need to shrink-fit it as it is just to prevent shorts and aid in wire identification. Determining which is the hot (black) and which functions as the return (white) is where you have to take your time and be careful due to holding your meter to see as well as holding your tester leads. If wired backwards, everything will still function, but your chances of electrical shock greatly increase. Grounding the fan green wire to the box will not help in preventing electrical shock in an ungrounded system. A remote control unit is probably the safest option besides an entire wiring upgrade.
Ceiling Fan and Light wall switch. Look with a flashlight into the back of the plastic box. That is were you may find the bare cooper ground lead for the replacement wall switch (4th wire). If the original fan light switch did not use the ground (3 wire) then the electrician would just shove the ground wire deep back in the box. Pull it out and ground the new wall switch. It could be safer.