Kitchen Cabinet + Downlights Wiring

Hi, I'm just about to start on a kitchen refit and have two sets of 6 downlights to wire up. Due to the layout of the Kitchen and wanting to be able to easily access/replace transformers I have the 12 Downlights across 6 transformers in configurations of
Cabinet Lights 3 + xfr, 1+xfr, 2+xfr Worktop Lights 3 + xfr, 1+xfr, 2+xfr
Each lamp is 20W, so I'm using 60W transformers.
My requirement is that the Cabinet lights and downlights are on 2 separatly switched circuits so Cabinets and Downs can be switched independantly (all Cabinets on/off, all Downs on/off)
I would generally wire this into the Lighting circuit, but I don't have a separate Lighting Circuit for the Kitchen (and no room to expand in the CU).
I have the following lights on the same circuit downstairs :
Main Room * 2 lamps = 200W (using 100W min rule) Front Room Candleabra (5 * 30W) = 150W Front Room Wall Lamps (2 * 30W + 1 * 30W) = 200W (using 100W min rule) HallWay (1 + 60W) = 100W (using 100W min rule) Understairs (1 * 60W) = 100W (using 100W min rule) Outside Light (1 * 60W) = 100W (using 100W min rule)
Downstairs ex.Kitchen Total therefore 850W
In The Kitchen I'll have 6 * 60W XFRs and say 400W worth of main lighting = 760W If I were to use the 100W minimum rule on each XFR, that'd be 1000W tho.
So depending on how this is calculated I could end up with a max total load of 1850W = 8A
The CU is a Wylex standard pluggable type and the pluggable MCBs are 5A for the Lighting Circuits.
Question is....
1) do the Transformers have to be taken as a minimum 100W per unit as per normal light fittings when calculating the load ? If I can calculate them at their rating, I end up with a total of 360W Xfrs + 400Main + 850W = 1610W = 7A. Or can I even take their actual load = 12 * 20W = 240W + 400W Main lighting + 850W Downstairs = 1490W = 6.5 (still over the 5A Circuit tho)
2) Is there diversity applied to lighting ? and is it sensible given that all downlights, cabinets and main lights are probably going to be on much of the time along with about half the lights downstairs at any one time ?
3) The LV XFRs come with Plugs so appear to be aimed at a Ring Main circuit anyway (for which i have spare capacity). However you can only have one socket per spur AFAIA and I would have 3 transformers distributed along the wall to wire onto the same switch..
any help much appreciated..
thanks, Ant.
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No, rate them at their actual load.

I can't remember if diversity is allowed on domestic lighting circuits. I suspect not, but am willing to be disabused. In any case, as a general principle, diversity is NOT allowed if the circuit is expected not to have an average usage pattern. I.e. if you intend to have all the lights on, then don't apply diversity.
Solutions:
1. Run the whole lot off a 5A FCU from a convenient ring main. You can wire each transformer up to the single FCU. Used a unswitched unit to supply the feed and then use standard light switches in normal locations.
2. Replace 5A MCB with 10A MCB. Probably not available. Not allowed if any lighting points have SBS or SES bulb holders.
3. Replace ancient fuseboard with modern DIN rail unit with spare ways.
I suspect you wouldn't even consider using low energy lighting...
Christian.
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Christian McArdle scribbled :

Really, I wasn't aware of that. I assume you mean SBC and SES though?
--
Gary
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That's what I said. ;-)
Christian.
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<snip>

Wiring off the ring main isn't a problem (since it's all being rewired). The only thing I wasn't sure of was this...A Spur can only supply a single socket, but I have 3 separate transformers that are required to be switched by a single switch (actually 2 sets to be switched by 2 switches). I'd plan on a single switched FCU and run 3 individual transformers off that, if that's ok ? If so can I run one length of 2.5mm from the FCU to a back box, take a feed off that for the first xfr and continue the 2.5 to another back box to provide the feed for the second xfr and contiue in the same way for the final xfr ? I don't plan on them being Sockets as such but the cables need to join in the back boxes somewhow (connector strip?)

I'd rather run off the ring main. are SBS/SES the smaller type bayonet/fitting ? if so, all of my downstairs lighting are standard size.

I would and do, but the next buyer may decide to put normal lighting in so I need to ensure the circuit is adequate.
Ant.
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"ANt" wrote | > 1. Run the whole lot off a 5A FCU from a convenient ring main. | > You can wire each transformer up to the single FCU. Used a | > unswitched unit to supply the feed and then use standard light | > switches in normal locations. | Wiring off the ring main isn't a problem (since it's all being | rewired). The only thing I wasn't sure of was this...A Spur can only | supply a single socket,
or double socket, or FCU. The key here is *Fused* connection unit. You can do (pretty much) whatever you like on the load side of the FCU because the fuse will limit the current being taken through the spur from the ring.
| but I have 3 separate transformers that are | required to be switched by a single switch (actually 2 sets to be | switched by 2 switches). I'd plan on a single switched FCU and run 3 | individual transformers off that, if that's ok ? If so can I run one | length of 2.5mm from the FCU to a back box, take a feed off that for | the first xfr and continue the 2.5 to another back box to provide the | feed for the second xfr and contiue in the same way for the final xfr | ? I don't plan on them being Sockets as such but the cables need to | join in the back boxes somewhow (connector strip?)
It might be neater to take T&E from the load side of the FCU to a double-gang lightswitch. From the lightswitch take one cable looping through the cabinet xfrs, and another cable looping through the downlight xfrs. (The 3 neutrals and 3 earths will need to be commoned in choc block at the lightswitch; suggest you use a socket depth box to allow room for the cables). This will avoid lots of fiddly junction boxes.
Because the circuit will be protected by a 5A fuse in the FCU you don't need to run in 2.5mm - 1mm should be adequate and easier to wire into the xfr terminals, which should be big enough to take 2 wires in each terminal to loop to the next xfr.
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great...thanks for the advice. Just need to gut the kitchen now....
Ant.
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"ANt" wrote | I would generally wire this into the Lighting circuit, but I don't | have a separate Lighting Circuit for the Kitchen (and no room to | expand in the CU). | I have the following lights on the same circuit downstairs : | Downstairs ex.Kitchen Total therefore 850W | In The Kitchen I'll have 6 * 60W XFRs and say 400W worth of main | lighting = 760W
In this instance it's somewhat irrelevant whether you rate the xfrs as 20W (for the one feeding a single light), 60W or 100W, as without them the circuit is already fully loaded (850W ex kitchen +400W main lighting).
As Christian suggests, make a new lighting circuit off an FCU from a ring. You could run it back to the CU and put the FCU by the CU so that when you get round to replacing the CU it's convenient to move the kitchen lights off the ring and onto their own circuit. There's no reason AFAIK why you shouldn't 'spur' off the ring at the point it connects to the MCB - the live terminal on the MCB will probably take 3 x 2.5mm cable ok, but check whether the neutral bar will.
Owain
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