Lighting Load Calculations

[FootSore]

I have done some digging through other posts and I have a couple of queries relating to the calculation of loads on lighting circuits.

My Circuits are like this:

Circuit 1 - Futronix P800 Controller controlling Lounge, Hall, Landing
Lounge - 6 * Ceiling Lights (LV 50W Transformers)
Lounge - 4 * Wall Lights (Baynet)
Lounge - 1 * Lamp Socket (Baynet)
Hall - 2 * Picture Lights (long tubes not flourescent)
Hall - 1 * Ceiling Light (LV 50W Transformers)
Landing - 2 * Ceiling Lights (LV 50W Transformers)

16* 100W = 1600W/240 = 6.66A (not OK?)
but unless someone takes out 9 lights and changes the transformers the max would be 9*50W + 7*100W = 1150W/240 = 4.8A(OK?)

Is changing a transformer considered the sort of thign a householder would do by mistake? Just like plugging in a few brighter bulbs?


Circuit 2 - Kitchen, Shower Room, Cuboard
Kitchen - 8 * Ceiling Lights (240V GU10)
Kitchen - 2 * 50W Transformers powering 4 * 20W halogens under cupboards
Shower Room - 4 * Ceiling Lights (LV 50W Transformers)
Cuboard - 1 * pendant (Baynet)

15 * 100W = 1500W/240 = 6.25A (not OK?)
but unless someone takes out 4 lights and changes the transformers the max would be 6*50W + 9*100W = 1200W/240 = 5A(OK?)


Circuit 3 - Other Downstairs rooms
3 * Rooms with only 1*Baynet fitting in each
300W - Wow compliance


Circuit 4 - Upstairs Master Bed, EnSuite,Bed 2
Master Bed (Futronix P400) - 7 * Ceiling Lights (LV 50W Transformers)
EnSuite (Futronix P400) - 6 * Ceiling Lights (LV 50W Transformers)
EnSuite (Futroonix P400) - 1 * LED System(50W DC Transformer)
Bed 2 - 2 * Ceiling Lights (LV 50W Transformers)
Bed 2 - 1 * Lamp Socket (Baynet)

17 * 100W = 1700W/240 = 7.08A (not OK?)
but unless someone takes out 16 lights and changes the transformers the max would be 17*50W + 1*100W = 1200W/240 = 3.95A(OK?)


Circuit 5 - Master Bath, Airing Cuboard
Master Bath - 6 * Ceiling Lights (LV 50W Transformers)
Airing Cuboard - 1 * Baynet

7 * 100W = 700W/240 = 2.91A Wow Compliance again


Have I understood this correctly?
What or who is Diversity?
Does it apply and how?

Does the 100W rule apply to LV lights - even the LED one?


Thanks

Dave

 

[Steve]

Why, when you know the exact wattage of all your lamps, do you insist on using the 100 watt rule? In reality, that is no longer used. Its an outdated and innaccurate method of calculating load. Go around and add up all your wattages and then come back to us.

Anyhow, its unlikely you'll ever trip your MCBs with those currents you've worked out, since you'd have to have all the lights on for an hour at least. This would never happen (unless you're trying to compete with Wembley stadium).

 

[SeanT]

(unless you're trying to compete with Wembley stadium).

I thought he was! Your leccy bill must be hideous...

 

[FootSore]

Electric bill not too bad - but everything is relative. Some of the rooms are quite big, Master Bed, EnSuite, dressing area is 10m*4m it does need a few lights.

The Lounge has 11 lights; 6 ceiling, 4 wall and 1 lamp. They are all wired through a Futronix lighting controller (like a Lutron) so they are never on together. Ceiling spots for reading, eating, playing. Wall lights for watching TV. Lamp is used if we are just chilling (aka drinking beer) and watching the fire.

Half the time the lights are dimmed which helps a little bit and if we aren't in the room the lights tend to be turned off.


Thanks for the pointers. If I can use figures as shown then I don't have an issue. My Electrician tends to take the most severe part of the regs he can find to avoid ever being wrong. He is not certain he can sign them off given the load calculations of everything * 100W

Is there any specific part I can point him towards.

I would have hoped the regs state something like max load a fitting can take. Which as lots of things were always baynets this would be 100W.

Otherwise you could argue that someone could take down a pendant and easily wire a light fitting with four bulbs so it should be 400W per fitting.

Thanks for any help.

Dave

 

[SeanT]

You can consider all the LV lights as a fixed load of 50W - the idea of the calculation is mainly around traditional ceiling rose fittings - each one should be calculated to be 100W, even if it is currently fitted with a 40W lamp (or even an 8/11W CFL!). This is still pretty pointless, as you can get 150W bulbs, but it's a good rule of thumb - you can then apply diversity (across different rooms / switches) of 66% - but again, it'd be stupid to apply diversity to a bunch of lights on the same one gang switch - you can apply it to the futronix controller though, although you should take the consumption of the controller into account if it draws more than a tiny bit. From what you've said so far, you're just fine - the 100w rule is just there to stop some idiot from wiring 30 fittings on the one circuit and putting 11w bayonet bulbs in each, which could subsequently be changed for a nice 3kW of incandescant....
Incidentally, can one put a larger than 6 amp fuse in a lighting circuit, if the cable and switches are rated for it? (I'm thinking 10, not 20 here!)