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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??

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  • I believe in the UK you need to be a licenced electrician to mess with the distribution board. Some of the users here are in locales with much more lax laws, and are allowed to do more than you are.
    – Criggie
    Jan 6 '19 at 22:02
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    @Criggie they're not asking about over-current switches, they're asking about switched fused connection units.
    – Niall
    Jan 7 '19 at 0:48
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    @Criggie Certain electrical works require notification to building control which depending on your local authority can be a pain if you are not a registered electrician. Notablly replacing the consumer unit or adding a new circuit, but that doesn't mean a DIYer can't open up the consumer unit to look at what is going on or to add wiring to an existing circuit.
    – Peter Green
    Jan 7 '19 at 2:04
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In the UK Fused connection units (FCU for short) are used for a number of applications including but not limited to.

  1. Providing over-current protection for a spur that serves multiple sockets or is wired in smaller cable than is allowed for non-fused spurs.
  2. Allowing a spur to be switched on and off.
  3. Providing over-current protection and/or switching for fixed appliances.
  4. Providing over-current protection for lighting that is fed from a socket circuit.

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.

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There isn't really a way of working where FCUs go other than to switch them off and try to find what's not working.

Absolutely can't find them? Could be...

  • They control sockets that you can't find (eg. kitchen cabinets have been built covering them)
  • The spur coming from them has been detached.

Is there a particular issue with them or is it just curiosity?

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  • Just curiosity!
    – Chris A
    Jan 8 '19 at 9:54

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