Lighting Circuit Question

[Rob1982]

I understand the reason for the ring circuit to return to the CU to be the following:

"In electricity supply, a ring final circuit or ring circuit (informally also ring main or just ring) is an electrical wiring technique developed and primarily used in the United Kingdom that provides two independent conductors for live, neutral and protective earth within a building for each connected load or socket.

This design enables the use of smaller-diameter wire than would be used in a radial circuit of equivalent total amperage. Ideally, the ring acts like two radial circuits proceeding in opposite directions around the ring, the dividing point between them dependent on the distribution of load in the ring. If the load is evenly split across the two directions the amperage in each direction is half of the total, allowing the use of wire with half the current-carrying capacity. In practice, the load does not always split evenly, so thicker wire is used."

Iv just run the wires in my electrical install and i have the lighting circuit returning to the CU which i now understand is wrong.

Can someone explain why we do this for the ring circuit and not for lighting?

thanks in advance guys.

 

[sparkyspike]

I bet you haven't wired your switch cables as part of the 'ring'.

 

[industryspark]

simply because its not necessary, its a pointless thing to do.

a lighting circuit requires very few amps in general domestic terms so the conductor (1mm/1.5mm) can easily carry this.

A power circuit (sockets) might have a much higher demand so we make a ring to give higher capabilities.

 

[industryspark]

simply because its not necessary, its a pointless thing to do.

a lighting circuit requires very few amps in general domestic terms so the conductor (1mm/1.5mm) can easily carry this.

A power circuit (sockets) might have a much higher demand so we make a ring to give higher capabilities.

 

[oharaf]

if you assume a lighting circuit is protected by a 6amp fuse and there exists a nominal voltage of 230v

then total power capability is 230 x 6 = 980 watts

Assuming the each bulb on the circuit is 60w then

980/60 = 16 bulbs thats quite a lot

If you were to do the same calc with an assumption of the use of CFL's at 11w

then 980/11 = 89 Bulbs that is a lot of bulbs

Even if you're into big bulbs of 100w

980/100 = 9 bulbs

We have 8 bulbs on our down stairs lighting circuit!!!

So really there is no need to supply from both ends of a 'ring'.

Thou I believe it can be done

 

[securespark]

There is no need with a lighting circuit. The currents drawn are much lower, so there is no need for a return leg.

Rings are wired like they are for the reasons you state.

The design of the ring final goes back to post-war Britain when raw materials were scarce.

Previous methods had been to run radials with one outlet per circuit, but this was seen as wasteful.

The new idea was to be able to quickly and conveniently wire a house with sockets, while being as economical as possible with cable.

 

[rssteve]

if you assume a lighting circuit is protected by a 6amp fuse and there exists a nominal voltage of 230v

then total power capability is 230 x 6 = 980 watts

Assuming the each bulb on the circuit is 60w then

980/60 = 16 bulbs thats quite a lot

If you were to do the same calc with an assumption of the use of CFL's at 11w

then 980/11 = 89 Bulbs that is a lot of bulbs

Even if you're into big bulbs of 100w

980/100 = 9 bulbs

We have 8 bulbs on our down stairs lighting circuit!!!

So really there is no need to supply from both ends of a 'ring'.

Thou I believe it can be done

mistake maby?

 

[Rob1982]

ok, thanks for the answers guys.

So my next question would be:

Since iv already mistakenly returned to the CU, can i just leave it the way it is? Does it still comply with regs that way?

 

[ColJack]

a ring is rated to take 32A but uses cable that can take 27A, so in theory a single point on the ring can draw 54A before the cables gets damaged but the breaker would trip at 32A protecting the cable.. there's also the fact that even a double socket is limited to a maximum of 26A ( 2x13A plug )

a lighting circuit in a domestic situation is usually rated at either 6A or 10A and is at minimum wired in cable capable of taking 16A ( 1mm² ) or more commonly these days 20A ( 1.5mm² )

I don't think that there's a regulation saying that you can't wire your lights in a ring ( as long as you don't try to put a 20A breaker on it or something ), it's just not the generally done thing..

 

[ebee]

your wiring may be unconventional but not wrong.
It may confuse someone in the future.
Steps to avoid that might be adequate labelling.
I know of someone who does ring lighting circuits.

 

[jockspark]

if you split it into 2 radials and you have a fualt you will only lose half
your lights this is assuming you have space in the cu if not leave as is
in theory it should extend the life span of the cable have used ring lighting speced on large areas shops factory space ect