Power consumption of 1 ampere

[Bill Gardener]

Looking at the lighting circuit in my new house I have realised that if all light fittings contained bulbs of the maximum allowable wattage and all lights were switched on at same time then it is seriously overloaded.

There is only one lighting circuit for the whole house and on top of this a

500w PIR floodlight and bugular alarm are also on the circuit.

My long term solution is split the house into two lighting circuits and move the 500w floodlight to its own MCB or maybe to a FCU on the upstairs sockets ring. The bugular alarm will also be eventually wired to a 3amp unswitched FCU.

But I would like to do a quick fix in the meantime to help me sleep at night.. So I aim to replace one of the upstairs sockets with a 6amp switched FCU and wire the floodlight to this.

But I don't know whether it is worth re-wiring the bugular alarm. The specs state that the power supply rating is at maximim 1A but nothing about the power consumption.

So my question is: What is the power consumption of 1 amp?

Thanks,

Bill

[Gary]

Bill Gardener scribbled :

Based on 240v then P=VI, Power(Watts)=Voltage(240v)*Current(1A) So 240 Watts would be the maximum consumption of the panel though I doubt it would get that high.

[ARWadsworth]

The fuse in my alarm (the internal fuse on the mains side) is 250mA at 250 volts. So the maximum power consumption is about the same as a 60 watt bulb. Personally I would leave the alarm on the lighting circuit and remove the

500W PIR from the lighting circuit (or better still remove the 500W light)

-- Adam

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[Andrew Gabriel]

Power consumption will be of the order a few watts, maybe 20W max if it takes a 7AH SLA battery and has to recharge it following a power outage, dropping back to a lower level when charged.

I would suggest leaving it on the lighting circuit as you will quickly be aware if that circuit fails, whereas you might not notice if a dedicated circuit fails (depending what the alarm does and if you are around at the time). Also, you don't want an alarm on an RCD protected circuit, and your ring circuit is more likely to be (now or in the future).

[Andy Dingley]

Look up "diversity". I suggest getting hold of a copy of the "On-site guide", which any electrical wholesaler will have, and which explains this.

Obviously it depends on the voltage. Power = voltage * current, so that's 240 VA. For a simple circuit (anything domestic except big motors) you can ignore the "power factor" and this is equal to 240 Watts.

-- Die Gotterspammerung - Junkmail of the Gods

[Dave Plowman]

I would imagine it's tiny, given that backup batteries are of the order of

3 amp/hour at 12 volts and last for several hours. I'd guess at maybe 10 watts or less. The fuse isn't a reliable guide as it has to handle the switch on surge of the power supply which might be considerable for a fraction of a second.

[Andy Wade]

Which leaves me wondering: if you don't know the answer to that (above), then how did you manage to work this (below) out?

Puzzled I am.

[Andy Wade]

But the usual rules allow no diversity within a lighting circuit: the maximum demand to be assumed is equal to the connected load, allowing a minimum of 100 W per lampholder - see Table 1A in the OSG. /Ipso facto/ a lighting circuit should not be overloaded when all the lights are switched on.

Diversity is allowed at the consumer unit or distribution board. For lighting the figures are 66% for domestic, 90% for shops and offices, and

75% for small hotels and guest houses.

[Christian McArdle]

The "1A" power supply is actually referring to the low voltage side of the alarm. In power terms, the alarm takes very little current at all.

A 6A lighting circuit can take 1.4kW of lighting, which is a lot, particularly if you use low energy bulbs rather than disgusting incandescent bulbs, which should be banned for the selfish waste of resources they are. Technically, you shouldn't have more than 14 pendant fittings on one circuit as you should assume 100W per fitting. That still makes a big house. However, if you use low energy lighting, then it is only a technical compliance issue and nothing to worry about.

As for the 500W light, I would suggest binning it. They cause immense light pollution, global warming and road safety issues. There is no sensible reason whatsoever for having floodlights on a domestic property. If you need to get from the driveway to the house, a 9W compact fluorescent light fitting on a timed PIR with daylight inhibition would be fine. If you want to sit out in the garden in bright light, do so in the daytime, rather than be single handedly responsible for flooding several Pacific islands and causing the failure of the Gulf stream.

Christian.

[Bill Gardener]

I believe that the maximum allowable load on a lighting circuit is 1200w. If all my light fittings contained bulbs of the maximum allowable wattage and all lights were switched on at same time then the power consumption is more than 1200w.

This is how I worked it out!

Bill

[Andy Dingley]

Haven't checked this, but aren't there rules allowing diversity when you're dealing with outside PIRs and similar ?

-- Die Gotterspammerung - Junkmail of the Gods

[Bill Gardener]

incandescent

I thought it was 1200w, at least my DIY book says so. Two of my light fittings take three 60 watt bulbs and in the bathroom there are three 60 watt spots. So 540W is eaten by three rooms alone. There are 8 other pendants. So this makes 1340W. With the floodlight this is 1840W. Way too much. This is maximum wattage by the way, I do have some low energy bulbs and most pendants have 60W bulbs rather than 100.

With regards to your comments about the floodlight I totally agree. But it only comes on for 20 seconds at a time when activated. It is not on all night!

I would like to get rid but the other half won't hear of it.

Bill

[Christian McArdle]

That would be an old 240V x 5A = 1200W circuit. Current designs should be for 230V x 6A = 1380W, even though the actual voltage will be 240V. The old system would probably be a 5A cartridge fuse in a fuse box. The new system would be on a 6A Type B MCB in a consumer unit. What do you have?

Christian.

P.S. If the spot fittings (not just any shades, which are easily replaced!) can only take a certain wattage (i.e. 60W max), it is reasonable to use that, rather than 100W.

[Bill Gardener]

Thanks Christain, it is a 6A Tyre B MCB, so I guess my DIY book is out of date.

So I have 1380W available, simply moving the floodlight will cure my worries then.

You may say then why not just switch it off, I would if there was a wall switch for it!

The joys of a new house!

Bill

[fred]

In article , Bill Gardener writes

You could save yourself a bit of work by swapping the bulb in the floodlight for a 300W instead of a 500W*.

You say you have either 60W or low energy lamps in you 8 'other' pendants, so:

540W (Big fittings) + 480W (8x60) + 300W (Flood) = 1320W (Panaaaah!)

No it does not meet the letter of the regs, but a degree of pragmatism in these areas works wonders, unless you really _do_ want to have a little play ;-).

• t'missus 'll never notice the difference, particularly if you do it when she's at the shops :) ps: 300W 117mm halogen lamps are avail almost anywhere, and under

2quid if you really look hard.

[Tim]

PIR + Gaffa Tape = Wall switch ;-)

regards Tim

[Jerry.]

Yes, but surely only in industrial buildings would 1201w (via 5 amp fuse) of lighting be switched on at the same time, if you plugged a 3kw electric fire into every 13 amp socket in an average domestic ring circuit and switched them all on at the same time you stand a chance of blowing the main company fuse off the wall - let alone the 30 amp ring circuit fuse !..

[Andrew Gabriel]

No -- it's not uncommon to end up with every light in the house on at the same time, unless the house is occupied only by the person who pays the electricity bill ;-)

By the way, industrial premises would normally have 10A lighting circuits at a minimum.

But you couldn't realistically do it even if the mains wiring could cope -- have you any idea how hot your house would get with 100kW of heat being given off in it?

[stefek.zaba]

Hmm, you've been spying on Casa Zaba than? ;-)

The previous poster is in any case dead wrong about blowing the main supply fuse: by deliberate design, the final-circuit-protection on the ring

- whether an MCB or a fuse - will pop well before the 100A/80A/60A cutout even thinks about popping; the magic term of art being "coordination".

But one of the odder sights at our site earlier this year was indeed a computer room full of about 60 fan heaters all going full pelt! We've put in a fancy-pantsy Utility Data Centre ("revenge of the mainframe") which we're using for internal server consolidation, for trials of rent-a-cycle, and for Customer Demos. The fan heaters were indeed all running, to put a 100kW? 120kW? heating load into the then-empty computer room, to act as a week-or-so-long stress test on the heavy-duty air conditioning upgrade! (Probably helped to make sure the wiring was up to snuff, too. Oddly enough, the 11kV?-to-415V-three-phase transformers for this building are physically rather close to the machine room with the tightly-packed racks of servers...) The heat management of the server racks continues to intrigue the engineering-minded among us: one of the factors in migrating the computing load around the servers is to set up a useful pattern of warmed-air circulation to help the aircon do its job most effectively!

Stefek, rambling again

[Steven Briggs]

In message , Bill Gardener writes

The 1A is probably the 12Vdc supply rating. The AC input is likely to around 15W, (about 0.065A) not worth worrying about or moving for now.