Converting 2 Way Switching To 3 Way - HELP!

Chazle · Post by **Chazle** » Fri Jan 04, 2008 12:43 pm

I am trying to convert the existing 2 way switching of our landing lights to 3 way following some building modifications - and the wiring I find behind the existing switches is somewhat different to the diagrams I've found on this site.

Junction box 1 is the four terminal loop in/out. Terminal 1 has red loop in, loop out and live feed to Junction Box 2. Terminal 2 has black (neutral) loop in, loop out and to lamp. Terminal 3 has earth loop in, loop out and to lamp. Terminal 4 has red to lamp and black to Junction Box 2 and is, I guess, switched live.

Junction box 2 is also 4 terminal. Terminal 1 has the red live in from JB1 T1 and red to Switch 1 com. Terminal 2 had black in from JB1 T4 and red to Switch 2 com. Terminal 3 has yellow from Switch 1 L1 and Switch 2 L2. Terminal 4 has blue from Switch 1 L2 and switch 2 L1.

On the back of the switches the existing setup is :
Switch 1, com is red live in from JB2. L1 is yellow to Switch 2 L2. L2 is blue to Switch 2 L1.
Switch 2 com is red to JB2 then to lamp - I guess this is called switched live.

I have installed an intermediate switch and run 2 x 2 core (brown and blue) 0.75mm flexes up to JB2. There are 4 terminals on the back of this switch, 2 labelled 1, one above the other, and 2 labelled 2, also one above the other. Cable 1, blue to top 1, brown to top 2. Cable 2, brown to bottom 1, blue to bottom 2. At JB2 I have connected the 2 browns to terminal 3 and the 2 blues to terminal 4.

Well, the fuse did not blow when I turned the power back on, but the switches do not work as they should, so something is not right and I can't figure it out! The existing setup is nothing like the 2 and 3 way switching diagrams on this website and I'm completely stymied - electrics have never been a favourite of mine!

Can someone please help me - this is the first of 2 sets I have to modify from 2 way to 3 way!

tim'll fix it · Post by **tim'll fix it** » Fri Jan 04, 2008 1:04 pm

the intermediate switch will switch the yellow and blue wires running from L1 and L2 on each switch with yellows on one side of the switch and blue on the other.

so at JB2 remove the yellow and blue wires from the JB

you will then need a new 4 way JB

connect one of the blue wires from switch 1 to one of the new blues cables
connect the other blue wire from switch 2 to the other new blue wire
do the same with the yellows and attach them to the browns

these four connections should all be separate

at the moment you have connected them all together

Chazle · Post by **Chazle** » Fri Jan 04, 2008 2:12 pm

Many thanks for the quick reply, I have another JB so I'll away to the garage then into the loft to re-connect things as you've described. Will let you know how I get on. Once again, my thanks.

Chazle · Post by **Chazle** » Fri Jan 04, 2008 3:11 pm

RESULT!! Rewired as you instructed, all tested and working perfectly. Can't thank you enough - I'd spent quite some time trying to figure it out for myself but had not even considered the correct way. Now to try to chase out the wiring of the stairway light for the same treatment.

This is really "Tim Fixed It For Me"!!!!