Re: Lghting Circuit Question

Yes. Its only using 11 watts so you can have 109 of those bulbs
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It is recommended you allow 100W min per lampholder, but you have to use common sense. Certainly, you can't assume that all lampholders will always hold only compact fluorescents.
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Andrew Gabriel wrote:

I believe the spirit of the regulation is that at any given time in the future, there is no combination of light bulbs and or fittings which could reasonably overload the wiring in the future.
6A is 1500W, or ten 150W bulbs, or 35 odd 40W bulbs. The gibbons who wired my house reckoned on at best two big rooms per circuit. But I have standard lamp sockets as well as wall lights and so on, so it was reasonable.
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No. You must allow 100W per fitting so that the cretin that buys your house doesn't take out the electrics when he decides he prefers that warm glow (i.e. global warming). If the fittings are only capable of taking low energy bulbs, then you may allow for the likely output of the fitting. (i.e. an 18W fluorescent strip fitting could be assumed to draw 18W, not 100W because you can't shoehorn a 100W GLS into it).
12 fittings is pretty excessive for a lighting circuit anyway. You should divide into several circuits so that a fault on one doesn't take out all your lights. Traditionally, one lighting circuit per floor is used. I prefer a random pattern, so that in the event of a lighting fault, several lights on each floor, and every other hallway still works. I think it is safer.
Christian.
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Christian McArdle wrote:

Yes, agreed.
Additional point, tiou alos need to guard aghainst the retrofitting of e.g. 8 2x40W wall lights where a single central 150W bulb used to do the same job :-)
An increase in ten of the current requirements.
I often wonder how Lawrence and Handy Andy manage all their fancy lighting...

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We have upstairs lighting, downstairs lighting.
Just went round and totalled up all the light fittings and came to 1194W, which is slightly scary.
The uplift of those nice Ring fittings which have 4 * 40w reflector lights on a single fitting is fortunately balanced by some low wattage bulbs, but I must be pushing the boundaries of safe lighting.
I am fitting a new ring main anyway, and have spare real estate on my consumer unit, so I think I will split off one half of this lighting onto its own circuit.
Shows that you should total up your light fittings each time you make what seems to be a minor change!
A slightly embarrassed. Dave R
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??
Well, not in this universe. 1.2kW on a lighting ring is not a problem.
When you've got 11 light fittings plus all the power sockets in 5 rooms including the kitchen ALL on ONE 5A lighting ring, then you may well have a problem. It has been known.
Regards, NT
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James,
What's poor power factor? Does this mean that an 11W bulb may be higher than 11W? If so,how much by?
Cheers!
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AFAIK - power factor does not have to be taken into account for domestic lighting installation.

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20W 220-240V 175mA, that == 40VA max
the circuit would have to provide the 40VA
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Rick Hughes wrote:

Thats because bulbs are essentially resistive loads.
Low energy ones probably are not, but they are so much less power anyway...it doesn'tr matter.

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Forgive my ignorance but what causes the phase shift then? Even if the shift isn't caused by these factors surely it can be offset by them. Capacitive / Inductive effects will still push the current around WRT voltage won't they? TIA, Richard.
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These appliances have negligable phase shift, and are neither capacitive nor inductive in nature. The low power factor is caused by them only drawing current at the peaks of the sine wave, so they are powered entirely from only a small part of the voltage waveform.
Actually, this is such a significant problem because of the number of such appliances, that the mains sine wave is noticably flattened at the peaks if you look at it on a scope nowadays.
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Andrew Gabriel

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writes:

ac (for want of a better phrase). Makes you wonder what kind of trouble we're heading for. The 3 phase supplies in some factories where I've worked have looked scary on a scope due to the effects of inverters and dc drives on the larger machinery.Then they take this crap to run computers and office equipment. Adding filtering on the input helps but surely they should try to stop the wave deformation in the first place. Thanks for the info Andy, regards, Richard.
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New EU regulations limit the harmonic Current distortion allowed by appliances. Low power appliances are still allowed to be low power factor, but higher powered appliances aren't. This is relatively new though, and lots of existing appliances don't conform. Large industrial users get charged a penalty for low power factor.
Just found a snapshot of the mains voltage waveform I took in our office a couple of years ago:
http://www.cucumber.demon.co.uk/bagmains.jpg
which is clearly badly distorted from a perfect sine wave.
--
Andrew Gabriel

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Of course. That's what I said wasn't it? ;-)
Christian.
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