Urgent wiring help FCU - wire question?

[floorwoes47]

Hi

I've been changing some old white sockets for chrome ones. All have been fine - just straightforward swapping over.

But I'm having difficulty with one which is a fused/switched socket. It is above worksurface and it operates the oven, extractor and hob ignition. (So there are three wires - one I think is the supply in and then the cables running up to the extractor and down to the twin socket where oven and hob are plugged in).

The problem is when I unscrewed the old one from the wall one of the wires just came loose (obviously wasn't in properly) so I'm not certain where it should go.

It's a live wire.

Also the old fused spur has terminals marked "N in", "N out" and "L in" and "L out".

The new socket refers instead to "N Supply L" and "Load L" and "N Load".

Am in a pickle as this fused spur is for the oven. hob and extractor which I need to be able to cook on!!

Please can anyone offer any guidance on this?

Two of the neutral wires were together in one terminal and it looks from the angle/lie of the reds that the one that's come loose was most likely with the other red next to it in the same terminal. I was going to just try this but don't know what the result will be - if it would just blow a fuse I would be happy to try it but not sure if it could damage the wiring system and/or the oven/hob which I don't want to chance!

Many thx.

 

[holmslaw]

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[floorwoes47]

Hi Holmslaw

Thanks for your reply - unfortunately I don't have a digital camera so can't take a picture.

I'll try to explain a bit better.

There is a fused socket above the worksurface. When this is switched off it isolates the extractor hood, oven and hob.

The extractor hood has it's own socket in the wall where it is plugged in with a normal plug. (The socket it plugs in to is linked to the fused socket because, like I say, when the fused switch at worktop level is switched off it isolates the extractor hood).

The same arrangement works for the oven and hob. The fused spur above worksurface level is linked to a normal twin socket beneath the worksurface, into which are plugged the oven and hob (by means of normal plugs attached to each appliance).

So in the wall at the fused socket I have 3 cables - one I assume is the mains power supply coming in. The other two cables are (1) running to the socket for the extractor and (2) running to the twin socket for the oven/hob.

I've worked out (I think) that the mains supply (live and neutral) go to the supply terminals in the fused spur. Then the two lives and neutrals from the other cables go together into the supply terminals.

But what I don't know how to do is ensure I am picking up the correct MAINS SUPPLY live wire to put into the supply terminal. This is because there was just this one wire which when I unscrewed the spur was loose so I couldnt see where it was coming from and don't know if it is the live mains supply or the live from one of the cables running to the other two sockets!!

Could I just try putting the mystery red into the Load or Supply - like I said I don't mind doing this if the result will be it'll just either not work or blow a fuse.

But if the consequences could be more dangerous then I shouldnt do this.

Many thx!!

 

[Adam_151]

Do you have a multimeter?

If so, make a plug up with a piece of wire linking live and neutral (ensure that you dismantle it later!), then with the power off, plug it into the oven and extractor sockets in turn, and use your multimeter to indentify the relevant cable by putting it on continuity/resistance range across L/N of each of the three cables you have, when you find the right one you should read a fraction of an ohm, the others should read overrange

 

[holmslaw]

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[floorwoes47]

Hi Adam 151

Thanks for your reply. I don't have a multimeter and this sounds a bit complicated.

Please are you able to tell me what would happen if I put the wires in the wrong place? Would it just trip a switch or could it do something more serious than this, like fry all the wiring or damage the oven/hob?

If I was confident that it just wouldn't work or would trip a switch then I don't mind wiring it how I think it should go, switching power back on and switching on say the extractor first to see if that works.

From the way the "rogue" red wire is lying I can guess at where it was in the old plug which seems to be 1 cable mains supply in and the two reds and two blacks from the other two cables being the cables feeding the socket above for extractor and socket below for oven/hob.

Many thx.

 

[holmslaw]

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[holmslaw]

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[floorwoes47]

Hi Holmslaw

Many thanks for your reply - yes earths are there I just didn't mention them to save confusing things further!

I know that I need to identify the supply cable but I don't know how to do this. Is there any way I can? Obviously the lives are bare at the moment (not wired in) and power is off.

The wall is newly tiled (which is why I'm now changing the socket covers) so I can't dig about unfortunately.

Of the three cables, one is coming from below and two are coming from above.

My best guess is that the wire coming from the top on the left side is the mains supply and the one on the right on the top is going up to the extractor. The one leading down from the box is going down to feed the socket for oven/hob.

Is there a danger if I put the wires where I think they should go, and check each appliance individually by switching it on and then switching off the fuse to check it is actually isolating each one?

If it doesn't then I should know the wiring is wrong and can try different permutations to narrow down which is the supply/mains cable.

I'm happy to do this so long as it won't actually fry my whole wiring system or blow up the hob/cooker - it's this I'm not certain about.

Hope someone can help as we had to get a takeaway last night as no oven/hob to cook on!!

Many thanks,

Susie

 

[holmslaw]

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[Adam_151]

I think thats a bit of an over-reaction tbh, I only advised the guy on the easiest way to bell out the cables with limited test equipment and without testing anything live, and made it clear that he shouldn't plug in the linked out plugtop to a live socket, and should dismantle it after he is done. If in the worst case it does somehow end up in an enegerised socket, yes there would be a bit of a bang, and either the plug top fuse or the breaker back at the board would operate.

Personaly I'd bell them out the other way round; shorting the disconnected cables at the FCU, and measuring at the socket outlets it feeds, but bit hard without a socket interface adapter

 

[holmslaw]

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[RF Lighting]

We use shorting plugtops at work all the time for taking R1+R2 readings.

I see nothing dangerous with adam's advice, yet you are advising using a voltage tester to test the end of the wires?

At least adam's advice doesn't require any live testing

 

[holmslaw]

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[electronicsuk]

Jeez, take a pill, holmslaw. If the advice given was followed to the word then there would be no risk involved to the OP, nobody was suggesting he/she insert a direct L-N link into a live circuit.