new circuit

[mikeypikey]

hi,im thinking about adding 5 outside spotlights to my house..well getting an electrician to add them...the problem is,i dont have room on my cartridge fuse board...however,could i add to an existing 15amp fuse which has 7 lights already on it?isnt there a way/formula of working out how many amps each bulb takes from the supply so that i know how many lights i can put on the 15amp fuse circuit?......im just a sucker for knowing how things work.....please inform me the best you can..thanks very much

 

[Paul_C]

Lamp wattage divided by operating voltage gives the current in amps, e.g.

60 watts / 240 volts = 0.25 amp.

Add up the wattages then divide the total by the voltage, or work out the currrents individually and then add them - You'll get the same result either way.

This works for regular filament lamps. If you have discharge lamps (fluorescent etc.) on the circuit, you might need to make additional allowances. And, of course, the cables all need to be suitably rated.

 

[mikeypikey]

hi,okay so i added up the total wattage of 7 energy saver 60watt bulbs and the 5 new cfl bulbs which are rated at 11watts each so added them together and i get 475watt and that divided by 220v is 2amps...am i correct in saying that im well under the fuse rating?

 

[Paul_C]

If that's all that's on the circuit, you have nothing to worry about at all. On a 15A circuit you could run over 3000 watts if you wished to.

Add two or three 500W halogen floods if you like!

 

[mikeypikey]

500 watt!! em no i dont think ill add them...the house is lit up enough as it is!lol ..........thanks for your help

 

[ericmark]

You will likely need to fuse down in some way. Most light fittings are rated 2 or 5/6 amp and normally as a result most lighting circuits will be fused to 5/6 amp.

With old tungsten bulbs there were fuses built into bulbs but some of the newer bulbs seem to be missing these fuseable links and when they blow then can weld themselves to the holders. I had some Ikea energy saving lamps which did this.

Although a BA22d lamp holder is often rated 2A I would say you are unlikely to get any problems if supplied through 5A fuse. But with 15A fuse you may get problems which although not dangerous are inconvenient when you need to change fitting to correct.