Lights on a ring

[bernardgreen]

I have been meaning to ask this for a while.

Is there a specific prohibition on lights looped at the ceiling roses being on a ring circuit of 1 mm ( or 1.5 mm ) that starts and ends at the same 6 Amp MCB

The advantage I see is that the ring is tolerant of a single fault ( loose terminal on the looped Live or Neutral ) without loss of any lights and with reduced over heating at the loose terminal.

 

[mikhailfaradayski]

i suppose there is nothing wrong with that idea, but it might make finding Zs un-necessarily awkward

Also, if a circuit is constructed correctly and maintained periodically, there shouldn't really be any faults

 

[holmslaw]

..

 

[tonyelectric]

The ring circuit is a peculiarly british idea, brought on by wartime shortages and subsequent low supply of copper, there are many in the electrical industry who reckon they should have been outlawed years ago, how many times have you found a broken ring leaving two radials woefully unprotected - I say ditch the ring next revision, go back to radials.

 

[bernardgreen]

how many times have you found a broken ring leaving two radials woefully unprotected - I say ditch the ring next revision, go back to radials.

I personally like the ring main idea when it is designed with protection that protects the cable should the ring be broken. The ability to survive one fault is (in my opinion) a benefit. With a loose connection halfway along a radial that loose connection becomes a hot spot as the total downstream load current is passing through it. With a loose connection on a ring the laod current is taken by the other side of the ring so the loose connection is to some extent protected from having to survive with full load current having to pass through it.

Perhaps the next set of regulations should ensure that rings are designed with breaks in mind and the protective device set at a value the cable in a single leg can safely carry until the device operates in an overload situation.

 

[AndyPRK]

On a lighting circuit it will just keep working and no one will have any idea there is a fault. Until a 2nd failure occours. So there is no advantage. (just confussion)

What would be better is two light radials off the same MCB.

More lights would continue to work under fault conditions and could later be split to another MCB if desired.

 

[RF Lighting]

Is there a specific prohibition on lights looped at the ceiling roses being on a ring circuit of 1 mm ( or 1.5 mm ) that starts and ends at the same 6 Amp MCB

Yes.

Regulation 433.1.5

 

[ban-all-sheds]

In what way does 433.1.5 prohibit, specifically or otherwise, a circuit as desribed by Bernard?

 

[RF Lighting]

Accesories to BS 1363 may be supplied through a ring final circuit, with or without unfused spurs, protected by a 30 A or a 32 A protective device complying with BS88-2.2, BS 88-6, BS 1363, BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO). The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5mm² except for two-core mineral insulated cables complying with BS EN 60702-1, for which the minimum cross-sectional area is 1.5mm²......

In what way does 433.1.5 prohibit, specifically or otherwise, a circuit as desribed by Bernard?

Lighting accesories do not comply with BS 1363.

RFCs must be wired in a minimum of 2.5mm² cable.

RFCs must only be supplied by a 30 A or a 32 A OCPD.

 

[martinxxxxxx]

Accesories to BS 1363 may be supplied through a ring final circuit, with or without unfused spurs, protected by a 30 A or a 32 A protective device complying with BS88-2.2, BS 88-6, BS 1363, BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO). The circuit shall be wired with copper conductors having line and neutral conductors with a minimum cross-sectional area of 2.5mm² except for two-core mineral insulated cables complying with BS EN 60702-1, for which the minimum cross-sectional area is 1.5mm²......

In what way does 433.1.5 prohibit, specifically or otherwise, a circuit as desribed by Bernard?

Lighting accesories do not comply with BS 1363.

RFCs must be wired in a minimum of 2.5mm² cable.

RFCs must only be supplied by a 30 A or a 32 A OCPD.

I disagree beacause as you say
Lighting accesories do not comply with BS 1363.

and therefore;as this rule written about supply to Accesories to BS 1363
it does not apply to lighting circuits.

If you follow my logic?

Martin[/b]

 

[RF Lighting]

No, it is a regulation written about ring final circuits, and it says that ONLY accesories to BS 1363 may be supplied by a ring final circuit.

 

[ban-all-sheds]

No it doesn't.

It allows the use of a 30/32 ring final serving BS 1363 accessories with a cable rated at not less than 20A etc as an exception to the normal rules in 433.1.1.

If Ib ≤ In ≤ Iz, i.e. the exemption for Iz ≤ In is not needed then 433.1.1 is satisfied and there is nothing prohibiting the circuit being a ring.

 

[ban-all-sheds]

In another thread one person expresses surprise at finding a ring on the lights supply.

And another comments that those who do ring lighting circuits soon learn not to.

So my question is what is wrong with a ring ?

Lighting circuits are not rings. They are radials.

Nothing is wrong with using a ring circuit to supply lights as such, but it is completely unnecessary to use a ring circuit. A radial is more than sufficient, and as such it is the convention to fit a radial.

Actually, I thought it wasn't unknown to use them on large installations, not to squeeze more capacity out of a cable of a given size a la "433.1.5 ring", but to reduce voltage drop?

 

[Adam_151]

I think ban is right on this one, Rob, in most situations you wouldn't want to find it, but nothing against it as long as you dont use a cable with lower current carrying capacity than the fuse, in the way you do a 32A ring for sockets

I certainly wouldn't expect to find it in a house (I have though- where a DIYer was been at work), but it could work well on bigger installs where you are up against volt drop to avoid increasing cable size.

I know of a school which is has the distrubution to the switchrooms wired as a ring, probably designed by someone who had worked for the supply authority at one point!

 

[martinxxxxxx]

No, it is a regulation written about ring final circuits, and it says that ONLY accesories to BS 1363 may be supplied by a ring final circuit.

Where does it say "only"?