Theory question - wiring lights

[benstoneham]

Just curious as to whether anyone can explain the reasons why the conventional way to wire lights is in series (i.e. from one to the next, with switched live between the rose/ dist or lamp itself) is better than supplying each lamp/ group direct from the switch (i.e. supply to multi-distribution point > to switch > to lamp/ light).

For example, if I take a simple lighting circuit consisting of 2 pairs of lights which are to be switched independently.

With the conversional way of doing things, we have 6 runs of cable :

1. supply > lamp1, lamp1 > lamp 2 lamp 1 > switch 1,

2. lamp 2 > lamp 3, lamp 3 > lamp 4, lamp 3 > switch 2)


Doing it in parallel (?), seems more efficient in terms of cable with 5 runs :

1. Supply > switches
2. switches > lamps 1-4


The obvious downsides I can think of are more conductors runing into the back of the switches and (maybe) a bit more work in 1st fix since everrything has go to be run back to the switches..

But, aside from this, am I missing anything else ? Are there any other advantages (e.g. circuit performance) anyone can think of?

Cheers.

 

[plugwash]

Generally the less joints the better. The loop in system was a pretty clever idea in that it both kept cable consumption and number of joints low. Unfortunately many modern lights don't do a good job of supporting it.

Another relatively common option is to loop through the switch boxes and then take a line from each switch to a light. This takes more cable and deeper switchbozes though.

Bringing back all wiring to a central point also has it's advantages but there is only any point if the central point is both easilly accessible and well labeled.

 

[ban-all-sheds]

With the conversional way of doing things, we have 6 runs of cable

4 of which just run from one light to the next.

Doing it in parallel (?), seems more efficient in terms of cable with 5 runs

4 of which run from the switch to the lights.

But, aside from this, am I missing anything else ?

Total amount of cable used?

 

[davelx]

You don't mean series, you mean daisy chain, which is a method of parallel wiring. Series is when there is only a single current path from L to N which passes through each lamp in turn - they would be very dim!

The method of wiring where a separate cable goes from the switch to each lamp is star wiring - but it's still parallel.

 

[benstoneham]

Yes, I see what you mean.. had I thought about it sensibly I would have realised that they must still be in parallel or they would be very dim as you say, apologies.

Ban-All-Sheds: I was actually thinking that the 2 groups would be switched from just 2 switches i.e. supply and 2 out from each switch.

Thinking about it though, does the loop-in system actually reduced the number of joins? for the same setup, I make it 10 for each approach.

A further point (and I suppose what was on my mind) is that as plugwash pointed out, many modern fittings (and in particular the HID fittings I'm looking at) aren't particularly well designed to allow multiple conductors..

In this particular instance, access to the area where the switches are is also good, so perhaps it is worth considering?

 

[benstoneham]

Doh.. I forgot the suply into the distribution point - make it 11 joins!