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.

1) do the Transformers have to be taken as a minimum 100W per unit as
per normal light fittings when calculating the load ?

No, rate them at their actual load.

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 ?

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.

Christian McArdle scribbled :
2. Replace 5A MCB with 10A MCB. Probably not available. Not allowed
if any lighting points have SBS or SES bulb holders.

Really, I wasn't aware of that. I assume you mean SBC and SES though?

--
Gary
Please remove #NOSPAM# if replying via email

2. Replace 5A MCB with 10A MCB. Probably not available. Not allowed
if any lighting points have SBC or SES bulb holders.

Really, I wasn't aware of that. I assume you mean SBC and SES though?

That's what I said. ;-)

Christian.

"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

snip
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, 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?)

2. Replace 5A MCB with 10A MCB. Probably not available. Not allowed if any
lighting points have SBS or SES bulb holders.

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.

3. Replace ancient fuseboard with modern DIN rail unit with spare ways.
yup agreed.

I suspect you wouldn't even consider using low energy lighting...

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.

"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.

"Owain" wrote in message ...
"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.
aha...champion !

| 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.
yup nice idea.

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.


great...thanks for the advice. Just need to gut the kitchen now....

Ant.