Why loop the live for lights?

[RobertKza]

I have one mcb in the consumer unit that supplies external lights. When this is off the coal shed, shower room main light and toilet light don't switch on.
There is a light switch in each of the shower room and toilet.
There is a 2 gang light switch in the shower/toilet access passage. One switch operates the passage light and I believe the other switch would operate the coal shed light (not tried it yet, the lamp holder looks in a poor condition). Two single core cables come into the 2 gang switch and two marked switch wires leave from the switch.

What puzzles me is that the two single core cables are each terminated in a 'common' terminal on each switch, but then a loop is fitted between the common terminals in the switch. Why would this be done?

My plan is to use the switched live going to the coal shed as the live wire (joined in the switch box, bypassing the switch) to a junction box in the now non used coal shed. From there I would have a switch in the 'coal shed' and run cabling for outside lights & switch in the back yard. Would it be OK to bypass the switch in the shower/toilet passage

Regards Robert

 

[littlespark]

The switches are are manufactured as two separate units on the same faceplate. The commons need to be linked to provide power to each side.

For additional switch and light, you would need to pick up the neutral from a light, the live from a switch.

Sounds like your electrics are wired in conduit, if it’s single cores. You don’t mention an earth wire though?
Not a problem if the metal conduit is providing the earth, but it would be prudent to have someone look at it with the appropriate testing equipment.

 

[RobertKza]

The switches are are manufactured as two separate units on the same faceplate. The commons need to be linked to provide power to each side.

For additional switch and light, you would need to pick up the neutral from a light, the live from a switch.

Sounds like your electrics are wired in conduit, if it’s single cores. You don’t mention an earth wire though?
Not a problem if the metal conduit is providing the earth, but it would be prudent to have someone look at it with the appropriate testing equipment.

Thanks. The single cores are each in their own sheath. The neutral single core has been run separately to the coal shed lamp holder. The earth wire has been terminated in the passage switch box.

 

[littlespark]

Ah ok… so it’s single-and-earth cables. (6241y)
I can see the green sleeved earth on the back box. (Check they all have an earth)

As before, only one of the commons comes from the mcb, the other one goes to the next switch on the line.

 

[RobertKza]

Ah ok… so it’s single-and-earth cables. (6241y)
I can see the green sleeved earth on the back box. (Check they all have an earth)

As before, only one of the commons comes from the mcb, the other one goes to the next switch on the line.

Wow, I never thought of that, so it's kind of a ring main! Would there be anything against taking the coal shed switched live removing it from the 1 way terminal and putting it with the common and then off to the coal shed?

 

[RobertKza]

Ah ok… so it’s single-and-earth cables. (6241y)
I can see the green sleeved earth on the back box. (Check they all have an earth)

As before, only one of the commons comes from the mcb, the other one goes to the next switch on the line.

On thinking, my idea of using the coal shed switched live wire connected to the common would create a spur from the ring and I've seen on YouTube that it's OK to create spurs. What comments would you have? Regards Robert

 

[littlespark]

Lighting isn’t wired as a ring, it’s classed as a radial circuit… so spurs off are just branches.

By moving the wire from l1 to common will leave the coal shed light on permanently, but that will give you a live/earth/neutral supply for anything else you want to do.


My advice is of course, isolate the supply before you do anything.

 

[RobertKza]

Lighting isn’t wired as a ring, it’s classed as a radial circuit… so spurs off are just branches.

By moving the wire from l1 to common will leave the coal shed light on permanently, but that will give you a live/earth/neutral supply for anything else you want to do.


My advice is of course, isolate the supply before you do anything.

Thanks for the isolation tip
My plan is to use the existing switched live single core cable (now connected to the looped (radial) live and bypassing the passage switch) together with the neutral cable (already connected to the existing lamp holder in the brick coal shed) into a junction box in the coal shed (As we no longer use coal this will be my equipment/tool shed). From the junction box I will run a circuit to the shed light fitting through a switch in the shed. The second lighting circuit from the junction box will be for the yard lights with a switch fitted near the back door!