Confused by loop-in lighting fitting

[riveralt]

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

I think this response and your original post has got BAS concerned.
The reality is that the diagram instructions are wrong (the blue and brown cables are the wrong way around and no sleeving on the switch live).
You thought they were wrong and therefore asked for advice regarding lighting circuits - but then you went and still wired it wrong!!!!!
Both browns (line) go to the loop terminal. The incoming supply blue (neutral) goes to the N terminal and the return switch live (blue with brown sleeve) goes to the L terminal. The earth wires should be sleeved and put in a connector block.
Similar piece of kit but correct Mk instructions here:
http://www.free-instruction-manuals.com/pdf/p47111398.pdf

 

[SimonH2]

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

I hadn't made that connection, but yes - he has all the social skills of Dr House or Dr Sheldon Cooper, and the same confidence that he is always 100% correct regardless of any evidence to the contrary

But on this he is correct, as others have said, it's really a bad idea to put the switch in the neutral. It means that you are 100% guaranteed to have live terminals in the lampholder even with the switch off. I think you should be able to imagine what that means if someone is changing a bulb - makes sure switch is off, check; assumes "power" is "off" in light socket, check; accidentally sticks fingers in socket while fumbling in dark & gets shock, check. Even if the shock itself doesn't cause injury or death, falling off the chair as a result may well do.

Yes, there are several "poor" assumptions there, but that's how most people change a light bulb. It's rare (IME) for people to go and switch the lighting circuit off at the consumer unit.

 

[JohnW2]

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

Look at a selection of his other posts (you have nearly 44,000 to choose from!) and formulate your own view about that - the latter pages of multi-page threads (which nearly always involve him!) are often the most enlightening.

IMO, his style is counter-productive (and sometimes totally unacceptable) and his 'people skills' almost non-existent, but he is very knowledgeable and his heart/intent are in this right place, even if he's his own worst enemy in putting his points across. On this occasion, he does have some valid points - in particular stressing the danger of having a switched neutral, and his uncertainty about whether someone who doesn't know/realise that should be dabbling with electrical things.

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?

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

Thanks, I completely see what you mean. The circuit needs to be broken BEFORE the light so that when you turn the switch off, the light is no longer connected to the supply.

However looking at the wiki etc, the 'proper' way is still not really obvious to me. They all seem to involve multiple lights, ceiling roses and junction boxes and just look rather complicated. If I just have 1 switch and one light fitting (as shown, with 3 terminals), surely things can be done very simply? Or do I still need to use a junction box? I'll check the wiki for a simple setup... this seems closest if I remove the "next light" part:

Just for clarity, the only thing I wired up was a light fitting directly to the FCU to test temporarily... nothing is actually wired up yet.

 

[d000hg]

Both browns (line) go to the loop terminal. The incoming supply blue (neutral) goes to the N terminal and the return switch live (blue with brown sleeve) goes to the L terminal. The earth wires should be sleeved and put in a connector block.
Similar piece of kit but correct Mk instructions here:
http://www.free-instruction-manuals.com/pdf/p47111398.pdf[/QUOTE]Thanks for that, their instructions on the 2nd page are seemingly for exactly the same fitting I have: "batten lamp holder having no rose"

However, your instructions and theirs don't seem to match? They say to connect all 3 wires L/N/E to the base, i.e. connect Earth to LOOP. I think the thing that's actually confusing me is I don't know what LOOP means. It seems you can use this fitting in two distinct ways and I don't know the terminology to clearly separate them. They are not talking about connector blocks or blue with brown sleeves in their very detailed step by step list... if you can help me understand that I'll be fine, it's the initial stumbling block of "what do all these words mean in terms of which wire goes where"

 

[stillp]

this seems closest if I remove the "next light" part:

That's correct.
the MK instructions are clearer than those you have - since you don't need to loop-in for another light, you can put the earth wire into your LOOP terminal.

 

[d000hg]

Perhaps I've actually made things harder for myself by trying to make it TOO simple? i.e. trying not to use any junction box "because it's just one light" is not the way people normally do things and so I find I'm doing something unusual?

The diagram I linked to makes sense so perhaps it's simply second nature that people would use one junction box for each light?

Quick side question on when a neutral-sleeved wire actually becomes live, etc, inside a box - is it acceptable to just wrap some insulating tape of the right colour or does one need to be more rigorous in how these wires are marked? Are you suppose to explicitly have it as brown with blue, to indicate it's a return wire which is still live, or could you just have it brown to warn people it's live?

 

[JohnW2]

Both browns (line) go to the loop terminal. The incoming supply blue (neutral) goes to the N terminal and the return switch live (blue with brown sleeve) goes to the L terminal. The earth wires should be sleeved and put in a connector block.
Similar piece of kit but correct Mk instructions here:
http://www.free-instruction-manuals.com/pdf/p47111398.pdf[/QUOTE]Thanks for that, their instructions on the 2nd page are seemingly for exactly the same fitting I have: "batten lamp holder having no rose" ... However, your instructions and theirs don't seem to match? They say to connect all 3 wires L/N/E to the base, i.e. connect Earth to LOOP. I think the thing that's actually confusing me is I don't know what LOOP means. It seems you can use this fitting in two distinct ways and I don't know the terminology to clearly separate them. They are not talking about connector blocks or blue with brown sleeves in their very detailed step by step list... if you can help me understand that I'll be fine, it's the initial stumbling block of "what do all these words mean in terms of which wire goes where"

'Loop' merely refers to a terminal provided for convenience to be used for connecting two conductors together, that terminal not being connected to anything else in the fitting.

IF (and it's a very big IF) that third terminal really is a loop terminal (as I've just described), then all you would have to do, in comparison with that 'dangerous' diagram you posted, would be to swap the brown and blues from each cable (so that both browns went into the 'loop' terminal), ideally put a bit of brown sleeving over the blue going to the switch (to indicate that it could be 'live') and 'do something' with the earths (e.g. as has been suggested, join them in a small piece of connector block).

However, to my mind, my big worry relates to whether or not that third terminal on your fitting really is a 'loop# terminal. Despite having 'loop' written on the fitting (perhaps because the same moulding is used for a fitting with a fourth terminal), you have told us that there is an earth symbol immediately adjacent to the terminal. If it is intended as an earth terminal, it could be connected to metal parts of the bayonet lampholder, then to do as I have described above would be very dangerous, since it would result in those (probably touchable) metal parts being connected to live electricity.

If you don't have the means (e.g. a multimeter) of ascertaining whether that third terminal is connected to any parts of the lampholder, I really think you either need to get an electrician to look at it or else get yourself a 'proper' lampholder, of reputable make, which comes with correct instructions.

Kind Regards, John

 

[stillp]

John, look at the MK instructions that riveralt linked to.

 

[stillp]

Perhaps I've actually made things harder for myself by trying to make it TOO simple? i.e. trying not to use any junction box "because it's just one light" is not the way people normally do things and so I find I'm doing something unusual?

The diagram I linked to makes sense so perhaps it's simply second nature that people would use one junction box for each light?

Quick side question on when a neutral-sleeved wire actually becomes live, etc, inside a box - is it acceptable to just wrap some insulating tape of the right colour or does one need to be more rigorous in how these wires are marked? Are you suppose to explicitly have it as brown with blue, to indicate it's a return wire which is still live, or could you just have it brown to warn people it's live?

Ideally, no junctions boxes would be used. Cables should be continuous between accessories.

 

[JohnW2]

That's correct. ... the MK instructions are clearer than those you have - since you don't need to loop-in for another light, you can put the earth wire into your LOOP terminal.

The OP doesn't need the loop terminal for another light but, if he wishes to use the arrangement that's been discussed (without a separate JB), then he does need that terminal as a means of connecting the perm L of the switch cable to the L supply.

As I've just written, my serious concern relates to whether it really is a 'loop' terminal, rather than an 'earth' terminal connected to exposed conductive parts of the lampholder.

Kind Regards, John

 

[JohnW2]

John, look at the MK instructions that riveralt linked to.

I have - but how do we know that the accessory the OP has corresponds with that? Would you be happy to assume that the third terminal on the OP's one (with an adjacent earth symbol) is not connected to any exposed parts?

Kind Regards, John

 

[riveralt]

However, to my mind, my big worry relates to whether or not that third terminal on your fitting really is a 'loop# terminal. Despite having 'loop' written on the fitting (perhaps because the same moulding is used for a fitting with a fourth terminal), you have told us that there is an earth symbol immediately adjacent to the terminal. If it is intended as an earth terminal, it could be connected to metal parts of the bayonet lampholder, then to do as I have described above would be very dangerous, since it would result in those (probably touchable) metal parts being connected to live electricity.

Can't comment on the OP's product - but as far as I can see the Loop/Earth terminal on the MK model is just a 'parking' area for the cables, whichever one you use and is not linked to any of the metal parts of the rose itself.

 

[stillp]

Exactly, reveralt.
John, it's a plastic batten lampholder. Does it have any exposed conductive parts?

 

[d000hg]

'Loop' merely refers to a terminal provided for convenience to be used for connecting two conductors together, that terminal not being connected to anything else in the fitting.

Aha, so a real loop terminal is isolated, just a way to pass through without needing a connector block to join the wires. That would make sense.

However, to my mind, my big worry relates to whether or not that third terminal on your fitting really is a 'loop# terminal. Despite having 'loop' written on the fitting (perhaps because the same moulding is used for a fitting with a fourth terminal), you have told us that there is an earth symbol immediately adjacent to the terminal. If it is intended as an earth terminal, it could be connected to metal parts of the bayonet lampholder, then to do as I have described above would be very dangerous, since it would result in those (probably touchable) metal parts being connected to live electricity.

If you don't have the means (e.g. a multimeter) of ascertaining whether that third terminal is connected to any parts of the lampholder, I really think you either need to get an electrician to look at it or else get yourself a 'proper' lampholder, of reputable make, which comes with correct instructions.

I see. Who'd have thought a simple lamp-holder could be such a mine-field. It was a cheap brand but sold on screwfix and with a lot of positive reviews from (one assumes) knowledgeable people - reviews from people talking about buying dozens of the things.

Exactly, reveralt.
John, it's a plastic batten lampholder. Does it have any exposed conductive parts?

I can certainly get access to a multimeter to test although from memory the fitting is all-plastic other than the wired terminals and the actual bayonet push-terminals inside.

I'm leaning towards the approach in the diagram I posted in which case the suspicious loop/earth terminal would just be used for the earth wire anyway.