Cable Question

[earnie]

Hi,

I realise that the single cable loading on a 1.0mm circuit is 1200w.
However, if you use circuits as a ring then am I right in assuming that you can double your loading as you've effectively doubled the conductor area?

Also, if so, would it theoretically be safe to run a 2.5mm (with loading of 2400w single run, 4800w ring), In a single run to the ring main of the lighing circuit?


Any ideas/Sugestions welcome.

earnie

 

[Goldberg]

What are you trying to achieve?

 

[earnie]

Just to supply a collection of lights without exceeding cable loading.

 

[Goldberg]

OK, but I suspect that you're going about it the wrong way.

If you're planning to run new cable, then you need to start by knowing the loading on the proposed circuit. Then you apply any relevant derating factors to arrive at the correct minimum conductor size.

 

[earnie]

i do, as it stands, my loading will be about 270W but thats as im using 9w LED gu10 bulbs (carbon footprint and save the whale and all the low power hippy crap). But if 50w GU10 bulbs were put in at some later stage, this would up it to 1500W so it'd be overloaded it on a single point cable run.

So just trying to cover eventualities as looping back with 1.0mm and running a single supply feed of 2.5mm is considerablely easier than rewiring the whole of the lighting.

 

[Goldberg]

Since 1.0mm² will easily carry 1500W (at 240V), I don't understand where your original concern is coming from.

If you have an existing circuit, what's the existing circuit protection?

 

[earnie]

my concern, well not really concern as we both know its able. but my question is, that the single loading for a single light run is 1200w. Mine may reach 1500w. This is overloaded. If i then turn it into a ring as i'll double the conductor area, am i right in assuming i can effectively double the load?

thats the main question!

my secondary, call it, interest question is : could i leave a lighting ring circuit (for example the one mentioned above), remote from the CU, and connect the ring to th CU using a cable of sufficient size in a single run?

Its on a 6A MCB at the moment so gives me just less than my 1500W, but obviously I can change that whenever.

 

[plugwash]

There is no hard 1200W limit just what your cable (which depends on it's installation method which you haven't told us) and breaker can support.

Using breakers over 6A on lighting circuits is not generally reccomended and is not allowed if you have an SES or SBC fittings on the circuit. If I were you i'd be looking to see if you can split this lighting circuit into two seperate circuits.

Wiring lighting circuits in rings isn't explicity prohibited but it's certainly unconventional

 

[Goldberg]

my question is, that the single loading for a single light run is 1200w. Mine may reach 1500w. This is overloaded.

I disagree.

If i then turn it into a ring as i'll double the conductor area, am i right in assuming i can effectively double the load?

No - that's in invalid assumption.

my secondary, call it, interest question is : could i leave a lighting ring circuit (for example the one mentioned above), remote from the CU, and connect the ring to th CU using a cable of sufficient size in a single run?

It's an unwise thing to do this to an existing lighting circuit without being 100% certain of the exact cable route, since there could be spurs that are acceptable for a 6A radial but that make conversion to a ring an impossibility without some rewiring.

Its on a 6A MCB at the moment so gives me just less than my 1500W, but obviously I can change that whenever.

Hmm.

 

[ban-all-sheds]

Wiring lighting circuits in rings isn't explicity prohibited but it's certainly unconventional

It is explicitly prohibited if it's done with 1mm² in order to have a bigger MCB than a radial would support.

 

[ericmark]

1) A ring main in 2.5 is limited to 32A yet 2.5 rated at around 20A so forming a ring will not double current carrying capacity because you are using parallel conductors of unequal length. See 433.4.1, 433.4.2, 434.4, 435.1 and 523.8
2) Lighting circuits normally include ceiling roses which have a max current handling of 6A even though 559.6.1.6 says 16A because of the limitation of the rose.

As to

It is explicitly prohibited if it's done with 1mm² in order to have a bigger MCB than a radial would support.

please give regulation numbers as although most insulations it would break one of the regulations I have quoted I can find nothing "explicitly prohibiting" it.

There have until this year been 150W tungsten bulbs which if they were fitted in all lamp holders in a house would in many houses resulted if all lamps were switched on you would get an overload but because the lighting is supplied from a 6A MCB or 5A Fuse we do not worry about what may happen in the future.

If someone wants to fit big lamps then that's their problem not yours they will have to upgrade the wiring at that point and there is no danger as overload will open should they change without the upgrade.

 

[mikhailfaradayski]

Has anyone considered diversity?

 

[ban-all-sheds]

As to

It is explicitly prohibited if it's done with 1mm² in order to have a bigger MCB than a radial would support.

please give regulation numbers as although most insulations it would break one of the regulations I have quoted I can find nothing "explicitly prohibiting" it.

433.1.1

 

[holmslaw]

..

 

[ban-all-sheds]

433.1.1, another badly worded reg that means standard ring circuits and parralel conductors are unacceptable, and that is nonsense.

It only appears nonsense because you don't know that ring finals and parallel conductors are catered for elsewhere.

Ring finals - see 433.1.5

Parallel conductors - see 433.4.1

To the op there is nothing wrong with installing lighting on a ring circuit, but there is no need and it's a pointless waste of money.

There is something wrong with it. It would be neither a 433.1.5 compliant ring nor a 433.4.1 compliant parallel conductor arrangement, and therefore would not comply with 433.1.1