Lighting circuits wired in rings?

[JohnD]

why would you want to wire them in a ring

 

[Click-Sure]

I can't think of any residential properties requiring high integrity earthing (which rings can bring in quite easily) either.

Finding a lighting ring as opposed to a radial in a house would certainally have me and most other sparks scratching heads!

 

[Spark123]

If you want to know about high integrity earthing there is a 21 page debate here!!!!
http://www.diynot.com/forums/viewtopic.php?t=132700&postdays=0&postorder=asc&start=0

 

[ban-all-sheds]

In theory if you had 4 lamps of equal wattage wired in a ring, there will be no current flow in the cable between the second and third lamp.

That is simply untrue.

Only if the bulbs were evenly spaced, exactly the same construction and cable length on both sides.

Even under these conditions.

 

[devans]

Cheers for the replies folks. Interesting to read about how rings may be used in the future... or maybe not!

Agree with holmslaw, seems sensible and common sense to limit the number of lights on a circuit (ie using a radial) and the track installation system seem logical. I think the lecturer has just got it wrong, these aren't new notes and I suspect he has just made an error and recycled his notes. I also noticed a couple of other errors, including the old phase colours etc.... maybe I'll direct him to this site!

Thanks for your help

 

[JohnD]

When I was young and ignorant, I learned about Rings for sockets and installed some. I just assumed that lighting circuits were done the same way but luckily mentioned it to someone before I started to run one.

Does your lecturer look young? Or ignorant?

 

[devans]

He's not young... but he is a bit of a know-it-all!

But to be fair to him he is very knowledgeable and is a very good lecturer. The services for this coming exam aren't in a huge amount of detail so I guess it isn't of great importance but I will definately mention it to him before the exam and make sure it gets corrected!

Cheers

 

[plugwash]

Only if the bulbs were evenly spaced, exactly the same construction and cable length on both sides.

Even under these conditions.

If the ring is perfectly symetrical and has an even number of lamps (e.g. there is no lamp at the midpoint) then the voltages at the lamps either side of the midpoint would be equal. Therefore there should be no current flowing in the cable between them.

Of course in reality no ring will be perfectly symetrical.

 

[holmslaw]

..

 

[ban-all-sheds]

Only if the bulbs were evenly spaced, exactly the same construction and cable length on both sides.

Even under these conditions.

If the ring is perfectly symetrical and has an even number of lamps (e.g. there is no lamp at the midpoint) then the voltages at the lamps either side of the midpoint would be equal. Therefore there should be no current flowing in the cable between them.

Ahh. Hmmm. Guess I need to post a few of these

I was thinking that no matter what the relative resistances of the various paths, there would always be some current in all of them - didn't think about the fact that in the theoretical case of symmetry there couldn't be current in the middle section because there would be no potential difference....