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lighting??


derek13

Question

havin a nosey at my cu i noticed 2 -1mm cables going into a single 6 amp mcb , with it being an old house was just wondering out of curiosity really , if this is / was a common thing in the past or present ? one of the cables it seems only feeds two lights in the front room and hallway ,while the other feeds upstairs lighting ???

by the way also have 10 amp feeding kitchen (recently refurbished before i moved in) which is wired in 1.5mm.

cheers guys:Y

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Possibly a shared neutral between upstairs and downstairs lighting circuits bud, and a 10amp MCB for a domestic lighting circuit is uncommon to say the least, probably all that the sparky had in the back of his van at the time.

AndyGuiness Drink

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I would not use a smaller cable on a circuit that was wired with 1.5 from the consumer unit

I know in practice it may seem safe but it is bad practice in my book also what would you right on the cert 1.5 or 1mm

Oh dear Adrian..... looks like its going to have to be hand-bags at dawn,

if I cant get you round to thinking to what IMHO is a bit more of a common sense approach.

I shall put my case for the defence your honour!Blushing:x

Mixed CSA's

In an ideal it may be nice to have a "college test bench" wiring arrangement..

but there are many situations where varying cable sizes do appear around a circuit.

Extend an existing installation with old imperil stranded core conductors.. and now use solid core conductors... thus CSA change.

Old 2.5mm with 1.0mm earth mixed with 2.5mm/1.5mm earth!

Situations where you quite simply do not know all of the CSA's around the circuit

Do a PIR and find multiple sizes into the same MCB/fuse, e.g. 1x1.0mm 1x1.5mm in same lighting circuit.

Any cases where I do find mixed CSA's on the installation I would note the "smallest" on the cert and ensure the fuse/MCB rating is appropriate for the cable capacities found.

Lighting circuit

A lighting radial circuit, could be considered as a central main "backbone" supply with individual switch drops taken off it at appropriate intervals...

e.g. looped at Ceiling roses or Switches or mixture of both.

Any individual switch drop off the main supply "backbone" will only be carrying the load for the light fittings that it switches, NOT the whole circuit!!:|

Thus a 1.0mm switch drop.. even if supplying say a 500w floodlight, typically is still carrying LESS than 2.5amps...

So no load issues for the smaller CSA switch cable!!

Many pendant type light fittings have a flex with 1.0mm or even 0.75mm flexible cord... This smaller cable CSA IS connected directly onto the lighting circuit.

So EVEN if the circuit is wired in 1.5mm the actual light fittings are very rarely wired with 1.5mm!

There are other reasons for using a larger CSA rather than just the current capacity...e.g. reducing voltdrop on a long run.

Some light fittings have very small terminal connections, which can be a bit tight for 1.5mm conductors.

So on a long lighting circuit it could be beneficial to have a 1.5mm "backbone"... but still leave switch drops and supply into light fittings as 1.0mm.

I rest my case your honour!:|B-)

please let me off leniently PrayPray

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I would only use 1mm for small houses (2 up/down), 2 way switching, CH and SD circuits.

AndyGuiness Drink

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I have stopped using 1.0mm now in preference to 1.5mm saves me some calculations with all this derating, bull poo, and carrying capacity.

However like Zeespark says for small installations it is still ok and ideal to use.

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I would only use 1mm for small houses (2 up/down), 2 way switching, CH and SD circuits.

AndyGuiness Drink

Indeed 2-way switching!;)

1.0mm 3core & earth can be a lot easier than 1.5mm, if you have got to pull cables down existing channels & chases to light switches on re-wires!

:D:)Guiness Drink

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Bugger me I am actually getting something right? been feeling like a right pillock with a few of My posts recently:p

AndyGuiness Drink

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Bugger me I am actually getting something right? been feeling like a right pillock with a few of My posts recently:p

AndyGuiness Drink

I feel like that with all my posts:^O

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But GH, you are more experienced than thee.

AndyGuiness Drink

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Bugger me I am actually getting something right? been feeling like a right pillock with a few of My posts recently:p

AndyGuiness Drink

You are most definitely NOT a right pillock my good sir!:)Guiness Drink.

;):x

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I feel like that with all my posts:^O

oh we ALL know you ARE a pillock GH!:o:P:^O:^O:^O]:)]:)]:)]:)

B-)

thats what Admin keeps telling us anyway!:|?:|

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I have stopped using 1.0mm now in preference to 1.5mm saves me some calculations with all this derating, bull poo, and carrying capacity.

However like Zeespark says for small installations it is still ok and ideal to use.

I use 1mm on lighting

no need to worry about derating 1mm on a 6amp mcb

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havin a nosey at my cu i noticed 2 -1mm cables going into a single 6 amp mcb , with it being an old house was just wondering out of curiosity really , if this is / was a common thing in the past or present ? one of the cables it seems only feeds two lights in the front room and hallway ,while the other feeds upstairs lighting ???

by the way also have 10 amp feeding kitchen (recently refurbished before i moved in) which is wired in 1.5mm.

cheers guys:Y

There is NO reason why you cannot branch a radial, (or spur off a ring for that mater) at the fuse box.

Sometimes it is the nearest and most convenient place to branch off to add new leg to the lighting circuit.

So 2, (or more!) 1.0mm in a 6amp MCB is not that uncommon.

also 10amp MCB 1.5mm? IMHO again NOT uncommon.....

I generally always wire my downstairs light circuit with 10amp type b MCB.

(all light circuits I wire on 1.5mm)

:):D

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Indeed 2-way switching!;)

1.0mm 3core & earth can be a lot easier than 1.5mm, if you have got to pull cables down existing channels & chases to light switches on re-wires!

:D:)Guiness Drink

I would not use a smaller cable on a circuit that was wired with 1.5 from the consumer unit

I know in practice it may seem safe but it is bad practice in my book also what would you right on the cert 1.5 or 1mm

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1.5 (6242YH), no need for an 18 odd amp cable (1.5 6243YH) to be able to energise a few light switches/fittings, 1mm would do that perfectly well.

AndyGuiness Drink

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There is NO reason why you cannot branch a radial, (or spur off a ring for that mater) at the fuse box.

Sometimes it is the nearest and most convenient place to branch off to add new leg to the lighting circuit.

So 2, (or more!) 1.0mm in a 6amp MCB is not that uncommon.

also 10amp MCB 1.5mm? IMHO again NOT uncommon.....

I generally always wire my downstairs light circuit with 10amp type b MCB.

(all light circuits I wire on 1.5mm)

:):D

Does anybody use 1mm for lighting anymore. I only use it for smokes and possibly heating controls.

Batty

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