Confused by loop-in lighting fitting

[d000hg]

In my other thread I was asking some basic questions: //www.diynot.com/forums/electrics/some-basic-lighting-circuit-questions.382047/

Now I look a bit more closely, I am more confused than I was before! This is my light fitting (sorry it's hard to get it to catch the light):

Untitled

• d000hg
• 4 Nov 2013
• 1

Untitled

• d000hg
• 4 Nov 2013
• 1

The wiring diagram shows a mains cable passing through the fitting, en route to a switch. Now, my school electronics tells me the neutral terminal here is actually not doing anything since a light is a one-wire affair - the live wire passes through the light to the switch, and the neutral comes back from the switch.

What exactly is going on inside this terminal - and can I use it more like this:
[code:1]FCU=========/switch/========light[/code:1]

In my second picture I think you can see the middle terminal has an earth symbol, which doesn't match at all the instructions. Is this saying I can attach live & neutral across the light and attach an earth wire to the middle one? Then I could do what I want... but I want to be sure I understand how the fitting actually functions internally.

 

[stillp]

Are you sure that middle terminal has an earth symbol? It's a loop-in terminal for the neutral.

 

[d000hg]

Update: a quick test says yes it does work that way... at least when I wired it to the FCU the light worked, nothing blew up and nothing was live that shouldn't be

Still would love to hear confirmation things are as I understand though.

 

[d000hg]

Are you sure that middle terminal has an earth symbol? It's a loop-in terminal for the neutral.

It seems to have both. In my photo you can see "LOOP" but to the right of it is definitely one of these:

 

[stillp]

What make is it?

 

[viewer]

In my other thread I was asking some basic questions: //www.diynot.com/forums/electrics/some-basic-lighting-circuit-questions.382047/

Now I look a bit more closely, I am more confused than I was before! This is my light fitting (sorry it's hard to get it to catch the light):

Untitled

• d000hg
• 4 Nov 2013
• 1

Untitled

• d000hg
• 4 Nov 2013
• 1

The wiring diagram shows a mains cable passing through the fitting, en route to a switch. Now, my school electronics tells me the neutral terminal here is actually not doing anything since a light is a one-wire affair - the live wire passes through the light to the switch, and the neutral comes back from the switch.

What exactly is going on inside this terminal - and can I use it more like this:
[code:1]FCU=========/switch/========light[/code:1]

In my second picture I think you can see the middle terminal has an earth symbol, which doesn't match at all the instructions. Is this saying I can attach live & neutral across the light and attach an earth wire to the middle one? Then I could do what I want... but I want to be sure I understand how the fitting actually functions internally.

Have a look at the Wikis. Normally the L, N + E pass through pendant part which is attached to the ceiling. They are often marked as loop. From this the live goes to the switch and back to the fitting (it may be marked L or SL). Although it is live it will be blue or black and is not neutral so needs a brown sleeve. One core of the flex to the lamp is connected to this terminal and the other is connected to the neutral in the pendant. The earth terminals on pendant loop and lamp are connected as you expected.

 

[ban-all-sheds]

In my other thread I was asking some basic questions: //www.diynot.com/forums/electrics/some-basic-lighting-circuit-questions.382047/[/QUOTE]
Please don't start a new thread.

The wiring diagram shows a mains cable passing through the fitting, en route to a switch.

This wiring diagram was drawn by a dangerously ignorant idiot:

Do NOT wire it up like that, with a switched neutral.

Now, my school electronics tells me the neutral terminal here is actually not doing anything since a light is a one-wire affair

I don't think you could have been paying attention in lessons if you think that a light will work with only one wire going to it.

the live wire passes through the light to the switch, and the neutral comes back from the switch.

How can a neutral come back from a switch if live goes to it?

I think you should stop doing, and do a bit of reading instead.

• http://www.google.co.uk/search?q=electrical+circuits+101
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• //www.diynot.com/wiki/electrics
  
  

What exactly is going on inside this terminal

Nothing "goes on" inside terminals....

- and can I use it more like this:
[code:1]FCU=========/switch/========light[/code:1]

A light can be wired like that, if you want.

In my second picture I think you can see the middle terminal has an earth symbol,

No, I can't,

which doesn't match at all the instructions.

Indeed not, but the instructions were written (at least in part) by a dangerously ignorant idiot.

Is this saying I can attach live & neutral across the light and attach an earth wire to the middle one?

If it is an earth terminal then it's a case of must attach an earth wire, not "can".

Then I could do what I want... but I want to be sure I understand how the fitting actually functions internally.

It's a lampholder - how hard can it be?

 

[d000hg]

In This wiring diagram was drawn by a dangerously ignorant idiot:

Do NOT wire it up like that, with a switched neutral.

So the people who make and sell millions of these fittings don't know how to wire them up? That's rather scary.

Can anyone else corroborate?

Now, my school electronics tells me the neutral terminal here is actually not doing anything since a light is a one-wire affair

I don't think you could have been paying attention in lessons if you think that a light will work with only one wire going to it.

I'm not sure if you're being deliberately awkward or didn't understand what I meant. My cable has 3 wires in it. I'm saying only one of these actually needs to connect to the fitting - snip the live and attach the two ends to the two terminals.

the live wire passes through the light to the switch, and the neutral comes back from the switch.

How can a neutral come back from a switch if live goes to it?[/quote]Um, the live wire comes from the live terminal of the FCU to the live terminal of the switch, with the light fitting in the middle. The neutral goes, un-broken, from the neutral terminal of the FCU to the neutral terminal of the switch... basically My First Circuit diagram.

What exactly is going on inside this terminal

Nothing "goes on" inside terminals....

Clearly since there are 3 terminals where the wires connect and only two inside for the light, something is going on

 

[EFLImpudence]

Can anyone else corroborate?

Yes.

 

[JohnW2]

Can anyone else corroborate?

Yes.

... and another Yes.

Kind Regards, John

 

[d000hg]

Is it obvious what they mean and it's a silly mistake or does it make literally no sense at all? Would wiring it as illustrated not work, or work but be dangerous - and if so why?

If they're selling them with bad instructions to people who would blindly follow them, I'm tempted to contact them. Quite likely tradesmen wouldn't even look at the instructions (as he said, it's just a light fitting) to notice this, so the only people at risk are those who don't know enough to realise they're at risk!

 

[JohnW2]

Is it obvious what they mean and it's a silly mistake or does it make literally no sense at all? Would wiring it as illustrated not work, or work but be dangerous - and if so why?

It would work, but would be potentially dangerous (which is always the case when one switches a neutral). The 'why' is pretty obvious. When the switch is 'off', the light will go off because there is no complete circuit (the neutral connection has been interrupted - however, there is still live electricity going to the lampholder, even though the switch is off - you can presumably understand why that is potentially dangerous?

For this reason, switching (of anything) should always been in the 'live' (line, phase) conductor, not the neutral.

Kind Regards, John

 

[ban-all-sheds]

So the people who make and sell millions of these fittings don't know how to wire them up? That's rather scary.

You can't see that the diagram shows the neutral being switched, but think you're OK to fiddle with electrics? That's rather scary.

My cable has 3 wires in it.

OK - L, N & E.

I'm saying only one of these actually needs to connect to the fitting - snip the live and attach the two ends to the two terminals.

So now you have a L going to one side, and nothing going to the other.

How's that going to work?

basically My First Circuit diagram.

This one?

[code:1]
---------------| LOOP |-----------------
SUPPLY SWITCH
___________________|____________________
[/code:1]

Um, the live wire comes from the live terminal of the FCU to the live terminal of the switch, with the light fitting in the middle.

Then where does it go? If "nowhere", then what's the point of having it go to the switch? If "somewhere", then what is the switch going to control, as it won't be this light, it's already got it's live supply - the cable goes there first, you said.

The neutral goes, un-broken, from the neutral terminal of the FCU to the neutral terminal of the switch...

Ah - it's a double pole switch then? Better be, if you plan on connecting a neutral to it.

And where does the neutral go then? You don't say it goes to the light, so (a) where does it go, and (b) where does the light get the neutral it needs?

Clearly since there are 3 terminals where the wires connect and only two inside for the light, something is going on

No, not inside the terminals.

And since you know that one of the terminals is an earth, not enough inside your head either, it would seem.

PLEASE stop fiddling, PLEASE get an electrician, and PLEASE don't try to do any more electrical work until you are considerably less clueless.

 

[bernardgreen]

That instruction leaflet needs to be sent to your local trading standards office together with the name and address of the supplier. That might prevent someone following those instructions and creating a situation which kills or seriously injures someone.

 

[d000hg]

...

Either I'm not explaining well (although nobody else seems to be having trouble understanding me), or you're bad at understanding, or you're being deliberately awkward. I'm not really interested in knowing which or why.

I know HOW electronics works in terms of physics, it's how the theoretical is translated into home electronics I don't know about. I don't know the terminology. If I can understand in electrical terms what the various fittings do, I'm good. But when you lack confidence and then are faced with instructions which seem to contradict what you think you know, anyone would assume instructions are correct. Hence you come to a forum to learn rather than fumble through.



People, is he just trying to play the Dr. House role?