Wiring lights in series

[bernardgreen]

Having Live and Neutral on a single change over switch is not a good idea.

This is "my" circuit using either 3 change over switches ( direct on mains ) or relays operated by ELV switches or intelligent controller.

B and C can be combined in a two pole change over switch if it is not necessary to have X bright and Y off

 

[AndyPRK]

Having ES lamps would not be a good idea in this situation.

 

[sparkwright]

Having Live and Neutral on a single change over switch is not a good idea.

This is "my" circuit using either 3 change over switches ( direct on mains ) or relays operated by ELV switches or intelligent controller.

B and C can be combined in a two pole change over switch if it is not necessary to have X bright and Y off

View attachment 82323

Excellent design, very likely something like this was used as uses basic 2 way switches and nothing unusual.

 

[JohnW2]

the regs cover every avenue in a normal domestic situation assuming only the normal is applied ... in other words it wont cover any unusual senario like this as its off on a tangent like you cant cover every possible senario within the regs iff you go off on a tangent to an area not specifically covered ... doesn't mean its complies just mean the senario is outside the scope off the regs

I don't really agree with that, and I don't even think your premise is true. BS7671 is not a set of comprehensive 'wiring rules' which renders particular circuit arrangements explicitly compliant. There are any number of very common aspects of domestic wiring which are not specifically covered/mentioned in it - I don't think you'll even finding any 'approval' of standard 2-way light switching there, let alone anything any more complex. Hence, the absence of mention of some particular wiring arrangements does not make it non-compliant.

If some aspect of an electrical installation complies with all relevant regulations in BS7671 and does not violate any regulations in BS7671, then I believe it is 'compliant'.

Kind Regards, John

 

[JohnW2]

Having Live and Neutral on a single change over switch is not a good idea.

Not ideal, I agree, but thats what b-b-m switches were made for, and why I stressed the need for one. However, I can't deny that your approach avoids that problem, and is therefore in that sence preferable. However, an issue with your arrangement, which could have safety implications, is finding a way of labelling the switches such as it would be clear to ('unfamiliar') users what they had to do to get the result they desired! In particular, in the absence of an overall on/off switch (which, admittedly, could be added) it might not necessarily be obvious to everyone what they had to do to render a particular lamp holder 'safe' (i.e. no L feed to it).

Specifically, it is more than a little worrying that switch B switches the neutral to lamp X. That means that if switch A is 'on', then lamp X can be switched off with switch B, but leaving a live feed to lamp X. I'd need to think about it, but such 'neutral switching' might (at LV) even be non-compliant with the regs. If it were a simple' lighting set-up, I certainly wouldn't be happy with a switch in the neutral, even if there was also a (separate) switch in the L, would you?

B and C can be combined in a two pole change over switch if it is not necessary to have X bright and Y off

Indeed - although labelling (hence potentially safety) remains a bit of a problem. However, as I said before, if (unlike you) we are talking LV, then I don't think you would be able to find a 2p2w switch as an 'electrical accessory'.

Kind Regards, John

 

[JohnW2]

Having ES lamps would not be a good idea in this situation.

Interesting point, and (although I'd have to look and think), that might be non-compliant with the regs. Similarly, as I've just written, I'm not all that happy (and not convinced about reg-compliance) of bernard's approach of having a switch in the neutral to one of the lamps which can be operated independently of the switch in the L supply to the same lamp.

Kind Regards, John

 

[bernardgreen]

having a switch (B) in the neutral to one of the lamps which can be operated independently of the switch (A) in the L supply to the same lamp (X) .

It doesn't matter which way switch B is when A is closed. The "neutral" side of lamp X is connected to Neutral either directly or via the other lamp. OK the voltage on the Neutral of X could be 115 which is not normal for a neutral but as regulations seem to allow for open circuit Neutrals becoming live via a lamp or appliance ( treat Neutrals as live conductors ) then they should allow a "Neutral" to be semi-live at 115 volts when the lamps are dimmed and live at 230 volts when they should be dimmed but lamp Y has blown or is missing.

 

[securespark]

Interesting.

I have not come across this nor remember it on here.
How many switches and lights are involved?

Hospital wall lights are wired this way.

 

[EFLImpudence]

I'm not all that happy (and not convinced about reg-compliance) of bernard's approach of having a switch in the neutral to one of the lamps which can be operated independently of the switch in the L supply to the same lamp.

What if light Y's Neutral was connected directly to N at switch B?

Would you still be concerned?


Edited 'cos I spelt Y wrong.

 

[securespark]

Having Live and Neutral on a single change over switch is not a good idea.

This is "my" circuit using either 3 change over switches ( direct on mains ) or relays operated by ELV switches or intelligent controller.

B and C can be combined in a two pole change over switch if it is not necessary to have X bright and Y off

View attachment 82323

It can be done with an ON/ OFF/ ON switch using a single lamp, but I can't find the diagram...

 

[endecotp]

B and C can be combined in a two pole change over switchView attachment 82323

If these are potentially make-before-break switches and if B-C is a single switch, then you can have a L-N short while switching through both switches.

 

[DetlefSchmitz]

IIRC, for an incandescent lamp, light output is roughly proportion to voltage to the power 3.4.

Came across this many moons ago:

Fair enough - that's an exponent of around 2.4, rather the 3.4 I suggested, so perhaps that's a consequence of my very fallible memory. Whatever, that graph only gives light outputs at 25% and 50% voltage of about double what I suggested (i.e. around 3% and 19.5% respectively) - so I think that my bottom line suggestion probably remains correct - that 2 lamps in series (across a source of the nominal voltage of one of them) is about as far as one can go if one wants significant light output.

Kind Regards, John

I'm not sure you noticed John, but the x-axis is not voltage, so the graph could be misleading.

 

[bernardgreen]

If these are potentially make-before-break switches and if B-C is a single switch, then you can have a L-N short while switching through both switches.

As yet I have not come across a standard main light switch that was make before break. My experience is that they are all break before make and the air gap from L1 to L2 via the faces of the moving contact is never less than 3 mm even when the switch is changing state. ( But I could be wrong due to in-experience )

I once came across a house where Live and Neutral were looped at the all the switches with Neutral and Switched Live going up the switch drop to the lamp. Two way switching was to have Live on L1 and Neutral on L2 at both switches and the Commons wired to either side of the lamp. Problems only occured with the inductive load of the two way switched flourescent lamp in the kitchen after the original tumbler switches were replaced with modern rockers. The breaking arc ( Lx to Common ) continued until the moving contact reached the other L and the arc was then between Live and Nuetral and a few times had maintained itself until the switch fell apart with smoke and flames.

 

[bernardgreen]

It can be done with an ON/ OFF/ ON switch using a single lamp, but I can't find the diagram...

There has to be a dropper resistance to absorb half the voltage or a choke or capacitor to limit the current through the lamp.

As the switch has only three states there can only be three states of lights OFF, One Bright, Both Dim ( or dropper / choke / capacitor in series with a single lamp )

A diode in series with an incandescent lamp will dim it but how much it dims will depend on the type of filament. Also a low wattage lamp with a thin filament ( low themal inertia ) will have a noticable 50 Hz "pulse" in the light from it.

 

[JohnW2]

having a switch (B) in the neutral to one of the lamps which can be operated independently of the switch (A) in the L supply to the same lamp (X) .

It doesn't matter which way switch B is when A is closed. The "neutral" side of lamp X is connected to Neutral either directly or via the other lamp.

What you say would surely not be true if, as per you diagram, switches B and C were independent (rather than being 'linked', as in a 2p2w). Unless I'm missing something, with the circuit per your diagram (switches B & C separate), with A 'down' ('on'), B 'up' and C 'down', lamp X would not be lit, but at least one side of it (both sides if the lamp were intact) of it would be at L potential - which is surely a potentially hazardous situation?

Kind Regards, John