10A RCBO for a lighting circuit...?

[plugwash]

That also assumes that every single light and both fans will all be on at the same time, which is not likely.

On what do you base this assertion that it is unlikely for all lights to be on at once, in my experiance it is almost a certainty when a property is fully occupied at least if there is only one light or group of lights in most of the rooms.

If a significant proportion of rooms have mulitple seperate groups of lights then it would be a bit rarer to have all lights on at once but i'd still expect it to happen every so often.

 

[Jacobssi]

Any fluorescent lighting? Eg kitchen?

 

[GaryMo]

Any fluorescent lighting? Eg kitchen?

I've ony got a 1 bed flat, but spotlights in most rooms (5 sitting room, 6 kitchen, 2 bathroom, so:
18 spotlights = 900w
3 normal dangley lights (2 entrance, 1 loft) = 300w?
2 extractor fans = ???w

 

[chapeau]

I currently have a 6A standard MCB covering the lights in my 1 flat. I'm getting an extractor putinto the bathroom and the electrician says it will take me over this 6A current and that as the wiring is 1.5mm he can fit a 10A RCBO.

I spoke to my dad and he's sure that you can only use 6A for a lighting circuit, so who's right?

Afternoon sarahw.

You appear to understand a fair bit and come on here often so what I would do is buy a copy of the IEE On-site-guide (ISBN 987-0-86341-854-9) which is very easy to understand and will let you find out these things for yourself.

Appendix 1 covers this subject and explains the two factors for lighting circuits.

Current Demand to be Assumed: Current equivalent to the connected load with a minimum of 100W per lampholder. So in your gaff, with 21 spotlights, that would be 2100W.

Amps = Watts/ volts

= 2100 / 230

= 9 Amps

To be safe, to that I would add the current drawn by the fans, on the box, call it x Amps . So current demand to be assumed = 9 + x

Then you apply something called diversity, which is an allowance for not having everything turned on at the same time. With lighting circuits that is 66% of total current demand.

So protective device has to allow

(9 + x ) x 0.66 Amps

As

9 x 0.66 = 6 on it's own then you are correct, quite close.

So that's the theory according to the regs, up to you how you want it putting into practice.

 

[GaryMo]

Current Demand to be Assumed: Current equivalent to the connected load with a minimum of 100W per lampholder. So in your gaff, with 21 spotlights, that would be 2100W.

I've ony got a 1 bed flat, but spotlights in most rooms (5 sitting room, 6 kitchen, 2 bathroom, so:
18 spotlights = 900w
3 normal dangley lights (2 entrance, 1 loft) = 300w?
2 extractor fans = ???w

50W per downlight as that's the maximum rating of lamp that can be used so 18 downlights equal 900W.

 

[chapeau]

So that's the theory according to the regs, up to you how you want it putting into practice.

 

[GaryMo]

Regs as regulatory (BS7671:2008) or a guide?

I suspect you actually mean it's a guide and not a 'reg' but it wouldn't be right to assume 100W for a fitting that can take a maximum of 50W would it?

 

[chapeau]

That is a very good point.

So 6A should do it

 

[ban-all-sheds]

Unless the assumption is that any lighting point could be replaced with a rose and a GLS pendant?

Which would make it 60W max these days...

 

[GaryMo]

The logic is still derived from a guide so I personally wouldn't apply more than 50W for a downlighter that can only take a lamp rated to a maximum of 50W.

In any case, I doubt anybody would replace 6 downlighters with 6 ceiling roses!

 

[ban-all-sheds]

True.

But they might replace a rose with a transformer supplying 300W or more of lights.

 

[GaryMo]

After considering 131.8

I'm getting bored at home now. Hope the weather improves next week!

 

[333rocky333]

With suitable cabling, the regs. allow lights with standard BC or ES fittings to be put on circuits up to 16A.

As well as most other BS lampholders including, ses and sbc.

 

[ericmark]

Use of over 6A protection device in lighting circuits.
134.1.1 Good workmanship by competent persons or persons under their supervision and proper materials shall be used in the erection of the electrical installation. Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.
311.1 For economic and reliable design, the maximum demand of an installation shall be assessed. In determining the maximum demand of an installation or part thereof, diversity may be taken into account.
314.1 Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.
530.4.1 Except where specifically designed for direct connection to flexible wiring, equipment shall be fixed according to the manufacturer's instructions in such a way that connections between wiring and equipment shall not be subject to undue stress or strain resulting from the normal use of the equipment.
559.6.1.6 Lighting circuits incorporating B15. B22. E14. E27 or E40 lampholders shall be protected by an overcurrent protective device of maximum rating 16A.

Because of 559.6.1.6 many electricians do think they can fit larger than 6A MCB’s however 134.1.1 where ceiling roses are used stops the use of anything over 6A because the manufacturer of the equipment rates the ceiling rose at 6A and it is the ceiling rose not the lamp holder which limits the size of MCB. If you have no ceiling roses then you could use a 16A MCB as 559.6.1.6 states.

In any normal house with each single outlet at 60W then design would allow a single 6A MCB except for 314.1 and where extras are added one would expect 311.1 to come in and parts of the lighting would normally be switched off. The exception is where heating is included into the lighting circuits as when rows of spot lights are arranged across a kitchen counter giving no more light than discharge lighting but also keeping occupant warm. Without this extra heat in already hot kitchens one would not get the extra moisture added to the food in the form of sweat.

Being more down to earth the cure is simple. If the MCB trips then replace a number of lamps with energy saving types. There is today no good reason to change the MCB to over 6A and her dad is A1 with what he has said.

 

[Paul_C]

Then you apply something called diversity, which is an allowance for not having everything turned on at the same time. With lighting circuits that is 66% of total current demand.

The diversity allowance for lighting in the regs. is for determining demand on feeders and sub-feeders though. It's not for application to individual final lighting circuits.

So if you calculate that the full load of the lighting circuit with everything turned on is 9A, you can use a figure of 6A for calculating the total installation demand, but the branch circuit would still need to be 10A.