Wiring problem

Mike UK

Mike UK

Mike UK

Soldato
Joined
20 Oct 2003
Posts
2,526
Location
Huddersfield
Hi All

Found a spur on top of the kitchen cupboards which I would like to add a socket onto. I bought a new socket and cabling and attached it so the wiring matched to what was connected but nothing no power.

I know theres no earth but I what I want to plug in doesnt require an earth.

The white wire is the electrical feed and the grey cabling feeds an outside light. Would it be possible its not working because the polarity is revered or something strange? Its connected to a seperate 3A fuse on the wall.

Any ideas? Thinking its probably one Ill have to get an electician in to sort.

http://i.imgur.com/7uZB5.jpg
Heres the spur in question and yes I know I need to clean the top of the cupboards :D
 
IMO you should always connect an earth, and you shouldn't wire a socket into a light circuit as light circuits are normally 5A circuits. You might not want to connect anything substantial into the socket at the moment but you never know in the future, best do it properly to begin with.
 
JohnnyG said:
Does it work when you switch the outside light on?
Click to expand...

Yep the outside light works. Thats what got me wondering why is the power getting to the light but not my crappy socket.

This is on the sockets wiring but I would like just to plug a CCTV transformer into it minimal power consumption really.
 
If that 3a spur for the light is on the ring final & taken from the back of a socket I'd try spurring your new socket off there.
There's no reason why it shouldn't work off that junction box assuming correct polarity is maintained.
 
JohnnyG said:
If that 3a spur for the light is on the ring final & taken from the back of a socket I'd try spurring your new socket off there.
There's no reason why it shouldn't work off that junction box assuming correct polarity is maintained.
Click to expand...

Worst part is the rooms just been newly decorated and I dont really want to rip it up to put a new cable in.

Only thing I can think of is the polarity must be reversed but wouldnt a no earth appliance still work if wired backward?
 
Assuming you haven't got a voltage tester you can open up the socket it's spurred off or the fused connection unit to see if the cables are correctly installed.
 
ahhh my bad :)

so its spurred from a ring main ?

How does the fused down bit work, trying to get a picture in my head. fused down to 3a before the spur for the outside light?
 
I'm going to assume it's done correctly ;)
Ring final is on 2.5mm, spur to FCU is on 2.5mm (so 32a on short run), FCU is at 3a, cable to lights after FCU can be almost anything with 3a fuse.
Spur off that to socket will only be able to handle about 750w due to 3a but at least cables will be protected :)
 
JohnnyG said:
Assuming you haven't got a voltage tester you can open up the socket it's spurred off or the fused connection unit to see if the cables are correctly installed.
Click to expand...

I have a multimeter but no idea how to check polarity not even sure if it does that (its a £4 el cheapass model) Just checked the fuse and its 13A but doubt it makes much difference.

Guess I could pick up a socket tester from eBay re-wire the socket in and give it a go.
 
lemonkettaz said:
ahhh my bad :)

so its spurred from a ring main ?

How does the fused down bit work, trying to get a picture in my head. fused down to 3a before the spur for the outside light?
Click to expand...

Whenever you add a new cable/circuit to an existing ring or radial you need to be very careful!
ALL cables in your house are protected by fuses or MCB's at the CCU, these are rated given the csa (thickness) of whichever circuit they are protecting.
This makes it physically impossible for cables to demand more current then they can safely carry.

However when you start adding thinner cables with smaller CSA this becomes dangerous because these new cables are not protected due to the fact that the circuit you are connecting them to has a higher rated current carrying capacity.
This means that the new cable being installed can demand currents that it cannot safely carry!
This is why whenever you add a thinner cable that has a lower CSA you should ALWAYS protect this new cable with a correctly rated in-line fuse/spur box.
You also need to design the circuit with the mind-set that a moron might be maintaining it :confused:
i.e, DON'T protect a 6A cable with a fused user access-able box as some numpty might come along and replace the 5A fuse with a 13A one!! (Obviously then that 6A cable becomes potentially very dangerous and could very easily start a fire:eek: :p )
If it's physically possible for a normal human to do then you must design the circuit to be 100% safe under them conditions!!)

Also don't forget a 2.5mm Ring final should be treated as a 5mm protected circuit and not a 2.5mm one, many a cowboy sparks make this mistake along with the 3-plate ceiling rose shocker!! lolZ

Always make sure your competent and confident on what your doing with regards to electrics as the potential to burn your house down is a real one!
 
Who cares what will be plugged in.
You can only design/erect a circuit to protect the cables & fitted accessories.
If an end user wants to fit a plug to their 10kw electric shower and try to run it off the 16a immersion circuit, good luck to them, at least they'll be no come back to the installer.
There's no accounting for stupidity.

And by the way, yes it is a problem if that FCU is fused at 13a, the manufacturer's instructions will specify 6a max for their light fitting and the switch is unlikely to be rated at more than 10a too.
 
lemonkettaz said:
If you are running a socket after fcu where its been rated to 3A, isn't that a start of problems, who knows what will be plugged in?
Click to expand...

I had a look and it's actually a 13A fuse. I'll be changing this to 3A as the halogen floodlight that was out there has been replaced with a LED unit. Like said only want to plug a 240 to 6v IP camera transformer so overloading it will be very unlikely.

For the multimeter I will check tommorow. What happens if an appliance is run with the wrong polarity go bang or fail to work?

Thanks for everyone's help so far :)
 
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