electricaluk
As I know some systems and terminology are different worldwide, I will start off the post by saying I live in the UK.
There are a number of fused switches in my flat. Some of them I know what they do – washing machine, oven etc, but others I have no idea. I've tried switching them off and on, but nothing happens. How do I go about figuring what they're for, if anything??
Zip on over to Edwards Signaling, and pick up one of these Motor Driven Industrial Sirens ($1090.00).
And a AdaptaBeacon Rotating Light ($972.00).
Wire them up to the switch, and enjoy.
You might also want to grab a pair of these.
For pranksters on a budget, you could get one of these 120V Selectable Output Horn/Strobes (~$50.00).
But you might want to cover up the word FIRE, to prevent confusion.
First thing I'd check is if the switch is even connected to any wires. You can probably check this just by removing the face plate.
You already checked the receptacles, but did you check both the top and bottom outlet? Sometimes a switch will only control one part of the outlet. In this case, the metal tab connecting both hot terminals is broken so that the top and bottom outlets can be individually powered (and switched).
The next step is to look at the wiring of the switch. First turn off the circuit breaker and test again with a non-contact tester (if you don't know what the switches do, then it could have more than 1 circuit in the box - just to be safe). Remove the switch and take note of the switch type - is it a single pole switch or 3-way switch? (If its a 3-way switch then the color of the traveler might be helpful in finding what it controls.) Is the line (from the circuit breaker) in this box?
If a visual inspection doesn't give you any clues then you need to trace the circuit. This is usually done with the power off using a circuit tracer:
A telecom probe/tracer can also be used in many cases. You hook the tone generator up to the wires at the switch, and then you use the probe to follow the wires through the wall. With any luck you will find your way to a ceiling or wall box. Depending how badly you want to know, you might need to open the wall (or use a scope) at some point to help trace the wire. More expensive versions of this tool exist that might be needed to find really sneaky wires.
It's not unheard of to find out that a previous owner dry walled over an electrical box, so keep this in mind as a possibility.
And if you just can't sleep at night without know where it goes, you could always x-ray your house as a last resort.
(source: tomcomunicacao.com.br)
(The above image is by photographer Nick Veasey. While this photo was stitched together, there are companies that x-ray buildings )
Best Answer
In the UK Fused connection units (FCU for short) are used for a number of applications including but not limited to.
The first thing I would do is look to see if the FCU has an open flex outlet hole (either on the front or on one of the edges). If so then it probably means that the FCU used to feed a fixed appliance that is no longer present.
If not then I would look for any equipment, sockets or flex outlets in the vicinity. Especially sockets that are in unusual locations (high up, under a counter etc) and test if those sockets are controlled by the FCU.
If you feel confident in doing so then removing the FCU from the wall (with the power off of course) and looking at what type and size of cable (if any) is connected to the load terminals may give more clues. Looking at the fuse may also give a clue, a 13A fuse likely means sockets or a high power appliance, a 3A or 5A fuse likely means lighting or a low (electrical) power appliance.