Downlights with a combined power greater than 1200 Watts

[Wet5park]

Looking for advice on a light circuit.

I am aware that each light circuit on a 6amp MCB shouldn't draw more than 1200 Watts (info from a DIY manual). With 6 rooms upstairs this shouldn't be a problem with 6x 60 or 100 watt bulbs....

however i am now installing Down lights with a max wattage of 50, and there will be a total of 25x 50 Watt lights (max of 7x50 watts in one room/ one dimmer the other rooms average 4x50) + 100 watts in the loft...

As the combined Watts on the up stairs circuit will now be 1,350 Watts do i need to either:

1. split the circuit, therefore have an extra 6 MCB, and have 675 watts on each?
2. Increase the MCB...and if so what size 10 or 32 amp?...and how is this calculated?
3. replace the standard 1.5mm lighting cable with 2.5mm?

Thanks

 

[oharaf]

okay.

6a x 230v = 1380Watts

you are saying

25 x 50watts + 100watts = 1350 Watts

So technically you are still within, however you are close to.

You could split the lighting circuit into 2 (on seperate mcb's if you please) and this would be fine

You could upto to a 10A mcb giving you 2300watts, but it is not neccessarily that easy, what size cable is in the lighting circuit? What does the cable run in? Insulation/clipped direct etc

If you split the lights then you're into needing to test and certify.

Any of these lights in the kitchen or bathroom or outside? Notafiable!!!

 

[electronicsuk]

Er... diversity? I don't think that the OP is suggesting the lights are all in a single room fed from a single switch. That said, please please please for the love of god don't install that much halogen lighting (cue BAS). It's not that I have anything against the fittings, just 230v halogen lighting in general. You could bring all that down to less than 300w if you use LED or CFL lamps instead, and your electricity supplier won't thank you for that either

 

[electronicsuk]

Er... diversity? I don't think that the OP is suggesting the lights are all in a single room fed from a single switch. That said, please please please for the love of god don't install that much halogen lighting (cue BAS). It's not that I have anything against the fittings, just 230v halogen lighting in general. You could bring all that down to less than 300w if you use LED or CFL lamps instead, and your electricity supplier won't thank you for that either

 

[JonoPashley]

Depending on the cable size installed and its installation method and the rating of the switching for these lights you could probably put the upstairs circuit onto a 10A MCB. This however would be Notifiable and should be done by a qualified electrician to ensure it is safe to uprate the breaker.

 

[rebuke]

That much halogen downlighting is ridiculous - think of the environment of the amount of power you're using, or if nothing else, think of your electricity bill!

 

[Wet5park]

Thanks oharaf for the quick reply. especially as i'm a novice to the site.

Great info on the fuse...should have worked that out myself due to past physics lessons. But needed the reminder, thanks.

Rather than being close, i think i will opt for the higher fuse, just incase some one changes a bulb.

Currently all the cable is 1.5mm, and there is a junction box for each room (6). The switch and down lights/transformers come from the junction box and the loop continues to the next junction box for the other rooms, there is a 1.5mm cable that links to each transformer via a click flow connector (sorry didn't mention that the lights are low voltage 12v)...but the wire from the transformer to the click flow is not 1.5mm single core, but 1mm multi core (right terminology?)

I assume that if i have a 32 amp fuse then i'll need 2.5mm cable...

Will 1.5mm cable with a 10am fuse be sufficient?...even if the transformer on each down light is smaller than 1.5mm

There may be 4x IP65 lights in a room that may one day have a bath in it ...but there isn't a bath in there yet...so its just a small room (will notify if a bath appears - thanks)

Will be getting everything checked when finished...

 

[rebuke]

One thing to be careful of if you insist on going down this route, is the rating of your lightswitches, you need to make sure they are appropriately rated, some might only be 6A.

(As a hint, you'll never find any rated to 32A, and even if you did you'd need more than 2.5mm cable - you only get away with 2.5mm on a ring main for sockets since it is a ring. The 1mm will probably be OK at 10A, depending on the length (even under >100mm of insulation it's rated to 10.5A, but the voltage drop might cause problems))

 

[Steve]

Will be getting everything checked when finished...

What does this mean?

And 12 volt lamps use more energy than mains voltage lamps. This is due to losses in the transformers. Each lamp will probably use 52 watts in total in real terms.

You would be better off with mains voltage lamps because then you could fit some with CFLs or LEDs - most transformers dont appreciate LEDs because they use too little power for them to work right.

If you havent bought the kit yet, please change it to mains voltage. So much easier to wire, and maintain. Transformers do fail, sometimes as often as the lamps.

 

[Wet5park]

Thanks Rebuke...

i accept the wasted power/ environment issues with the halogens...and maybe a decent LED might be developed/tried...I have offset some of the environmental issues with water recycling in regards to rain water collection for lavatories, garden tap and washing machine etc...also suspect that softer room lamps will be used (but i'm not the interior designer...i just do as i'm told) (sorry if i anger any environmentalists)

Thanks for the info in regards to switches and i'll check these...if they're 6amp then it looks like i'll split the circuit and add an extra 6 MCB to the consumer unit.

And also for the additional info in regards to 2.5mm on a ring main.

Glad i've found this forum

 

[oharaf]

Matthew, Diversity, sorry!!!!!

Wet you say these down lighters have TRANSFORMERS on them??!?!?!

I really suggest you get a sparky in I'm not entirely convinced you are up to the job.

 

[Wet5park]

i've opened a real can now.

Steve...Once the work is completed i have an electician mate who'll check that i haven't done anything stupid but don't want to keep pestering him with every question i have. I'm not doing anything unless i'm sure i know what i'm doing...hence asking opinions here...and the work is being done on my own house, and not a buy to let (which i don't have)...therefore i have no intention of living in a death trap

All the kit has been brought and the choice was based on the need to have cool (re temp not fashion) light fittings that could fit in a narrow space...these required transformers (so i was advised)

 

[Wet5park]

Oharaf...now i'm concerned.

Whats the issue with the Transformers...each light is low voltage and therefore required a transformer per light (so i was informed).

Whats the issue with the transformers?

 

[ElectricDunc]

Will be getting everything checked when finished...

You would be better off with mains voltage lamps because then you could fit some with CFLs or LEDs - most transformers dont appreciate LEDs because they use too little power for them to work right.

If you havent bought the kit yet, please change it to mains voltage. So much easier to wire, and maintain. Transformers do fail, sometimes as often as the lamps.

Aurora do a 12V CFL, decent 12V LED's will retro and don't forget IRC halogen. No need to go GU10 just to save electricity these days.

Seriously though please apply diversity. Do you really expect to have every single light on in your house at the same time?! Yes, 6A at 230V is 1380W but i doubt your supply voltage will be that low so your current will be less then the calculated current anyway. Isn't it 80% of final demand for lighting circuits when diversity is applied?

 

[Steve]

All the kit has been brought and the choice was based on the need to have cool (re temp not fashion) light fittings that could fit in a narrow space...these required transformers (so i was advised)

Very sorry to inform you, halogen lights are the hottest filament lights you can buy.

This is why they are so dreadfully inefficient.