Hi,

I am in process of converting my detached workshop into a study and
storage room. I am OK with wiring for electric power, which I have
completed but do not understand light wiring especially when I have
two way switched etc.
All I want to do is finish off the ceiling this weekend but source
electric cables for light fillings and light switches before I finish
off the ceiling, so that the electrician can come over and finish the
job.
As it is hard to explain all here, I have put a diagram at
http://wrkshoplight.freewebpage.org all I want is someone in the know
how to tell me how and where to route the cables for the electrician
to finish off the job.

The wall mounted fan and heater is a luxury I will look to add latter
on but want to do the prep work now! Do I need to put these on there
own circuit or can these be part of the lighting circuit? My consumer
unit does have input to take 4 separate fuses - if this helps.

You can email me directly at or reply here. Please do
not pay much attention to the pictures, as these are the best I could
do – the text explains all what I am trying to achive.

Thanks

Jag Mann

OK. Firstly, the heaters should be on a separate circuit and definately not
sharing with a lighting circuit. The fans could come off the lighting
circuit if wished.

BTW, cable colours are changing. New colours are in brackets.

You have a 2 way and a 3 way lighting circuit.

The 2 way circuit in Room B is wired as follows, using 1.0mm2 or 1.5mm2
solid cored twin and earth mains cable, not flex.

Place the main junction box in a convenient accessible location. You can use
a separate junction box, or use the one often incorporated into one of the
light fittings. When you use the incorporated one, it is called "loop in",
whilst if separate it is called the "junction box" method. Both are
electrically identical.

There will be 4 terminal blocks.

1. Earth. All earths should be terminated here. Ensure you use green/yellow
sleeving over the bare earth conductors.
2. Permanent live. The incoming unswitched lighting circuit comes in here
(and may also go out to the next junction box for Room A)
3. Neutral. All neutrals connect here.
4. Switched Live. A switch cable is connected between this and the permanent
live. Use the black (or blue) wire for the switched side, but use red
sleeving over the top to indicate that it isn't a neutral. All the bulbs are
connected between this terminal and neutral.

Now, the switch cable goes to the first switch. This switch should be a 2
way type, with 'C', 'L1' and 'L2' terminals. When using a dual gang switch,
ensure you have got the right terminals for the particular switch and not
mixing the 'C' from one switch with the 'L1' from another, for example.

Take the switched live to the 'C' terminal. Then, take a 3 core and earth
cable from here to the last switch. The 3 core cable connects as follows.

(1st switch end)
Red (brown) - connect to the permanent live from the switch cable, using an
insulated crimp terminal and then using additional insulation tape or
heatshrink over the top.

Yellow (grey) - connect to L1
Blue (black) - connect to L2

(last switch end)
Red (brown) - connect to 'C'
Yellow (grey) - connect to L1
Blue (black) - connect to L2

If you need an additional switch (such as for Room A), the wiring is
identical, except that any additional switches required are connected as
follows:

The cable between the 1st and end switch must be routed via the intermediate
switches. Careful consideration of the optimum cable routing is required, as
is choice over which switches should be the 1st and end switch.

The switches used must be the expensive "intermediate" type. These are often
only available as a single faceplate item. When you want two switches in one
single faceplate, you may have to search for a suitable item, use a grid
type switch, or reorder the switches, so that the dual gang switches are
always at the end of a run.

At the intermediate switch(es), connect the red (brown) cables to each other
(but not to the switch). Sometimes, if careful, you can remove the sheath
from the cable and not actually cut the red (brown) conductor at all, saving
you the bother of crimping them back together. Then, follow the instructions
that come with the switch to determine which terminals to connect the yellow
(grey) and blue (black) wires to.

Note that the alternative sometimes suggested of running separate single
cables from the junction box to the 1st and last switch in the chain is no
longer considered acceptable, as it interferes with audio equipment,
particularly hearing aids. The feed to the end switch should go down the
same cable as the other conductors to avoid earth loops.

However, as it seems that you are using an electrician anyway, the critical
things to remember a

2&E from the incoming light circuit to the junction box.
2&E between the junction boxes.
2&E from the junction box to the first switch in the line.
3&E from the first switch, past any intermediate positions to the last
switch.
2&E from the junction box to any light fittings. If multiple, then these can
run in a daisy chain, or each directly back to the junction box.

Ensure the cable you use is consistent in colour coding. Ensure it is at
least 1.0mm2 CSA. Ensure that it is proper fixed wiring cable with solid
cores, not flex or bell wire.

Christian.