Fuse in lighting circuits

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I have a little query that I have failed to get an answer to from various sources.

My house was build in 1992 and has RCDs in consumer unit but with cartridge fuses rather than MCB (which is fine)

As you would expect the lighting circuits are separate upstairs and downstairs.

However in both circuits I have a single fused plate with a 13A fuse in it. As far as I can tell the lighting circuits run into this fuse plate, but not "through" it. Ie. Black into north terminal, black out north terminal. Red into south, red out of south. So the fuse is accross the positive and neutral loops.

It makes no operational difference whether fuse is present or not and my guess is it's somehow related to safety in the circuit, but what? Do I even need it at all?

Thank you

Richard
 
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As far as I can tell the lighting circuits run into this fuse plate, but not "through" it.
Can't work out what that means.


Ie. Black into north terminal, black out north terminal. Red into south, red out of south.
Could you try again using "Supply" and "Load"?


So the fuse is accross the positive and neutral loops.
It's not "positive" - it's "line", or, more commonly, "live".

As it's AC the voltage of the line with respect to neutral varies between +325V and -325V.

And there's no way a fuse will survive being connected between line & neutral.


It makes no operational difference whether fuse is present or not and my guess is it's somehow related to safety in the circuit, but what? Do I even need it at all?
If it doesn't do anything to the lighting circuit then clearly you don't need it for the lighting circuit.

But then FCUs are not used to do anything to the circuit which supplies them.
 
Yes, I'm not describing it very well, but then I dont really know the terminology.

I attach a rough sketch of what I saw (thought I had picture, but apparently not). I have two 3 core cables running into box connected as shown.

I agree with you though, I dont understand why it doesn't just blow? I can only imagine that it must be doing something else beyond my comprehesion but what, i don't know. Any ideas?


If this still makes no sense at all, I'll have to take another look to see if I can find any more clues.

Many thanks,
Richard
 
Do the two red wires actually go into one terminal? Do the two black wires go into one terminal, or two? How are the terminals in use labeled?
 
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From your drawing it actually looks as if the FCU is being used as a loop in loop out junction box.
 
Can't say for sure, so I'll take a closer look and post findings

Thanks
R
 
@riveralt

Yes, but with a fuse? There is another one downstairs which I will also check. They appear to be contempory with the original build.
 
Unless you can read the terminal markings, you can't really be sure the wires are connected across the fuse as you describe.

I would expect the two reds to be in the L 'feed' terminal and the two blacks in the N 'feed' terminal.

Could these be fused spurs that were fitted for future use? Where exactly are they situated in the house?
 
I will confirm tonight and get some pics

One is in the bathroom(!!) and the other is in the under stair cupboard.

R
 
Right, after all your comments I had another look. I think I can see what it's doing now, if not why it's there.

The fused plate as (pictured) shows it's just in the circuit and just not connected to anything, as is the other one down stairs. What these were intended for I dont know. The only other oddity is the large earth connection that I think runs all the way back downstairs to the consumer unit.

Thanks for all your queries that cleared this up

 
Where in the house is that FCU?

My guess is, it was installed to feed an item of equipment, which you don't have.

A small heater in a bathroom, etc...
 
That one is in the bathroom. There is another one downstairs under stairs. There is a small electric heater in bathroom but is connected via it's own 35a spur.

I guess they were put in at build time but just never used. As they are on the lighting circuit their usefulness is limited but I imagine a lit cabinet/shaver socket would be ok
 
The only other oddity is the large earth connection that I think runs all the way back downstairs to the consumer unit.
How sure of that are you? Given that it's in a bathroom, it's possible that it's a 'bonding' connection to local pipework. If that were the case, it's been done in a pretty iffy way, since the conection between it and the 'earth' conductors of your wiring is dependent on the contact/screw beween the earthed parts at the back of the switch and the metal back box - it would have been better if there were an explicit connection bewteen that fat earth wire and the earth terminal in the back box.

Kind Regards, John.
 
Interesting thought, it could well be. But if so it will hidden behind all the boxing for the pipe work before running down to ground.

R
 

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