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Extending Lighting Ring Main Into Loft

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raybush | 17:10 Sun 24th Jan 2021 | DIY
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I want to extend my upper floors lighting ring main into the loft .
What i need to know is ,the lighting fuse is rated at 5amp to which i already have 6 x 60 watt bulbs running and 7 x GU10 - 9 watt low voltage spot lamps .I'd like to install possibly 3/4 60 watt bulbs but , i don't want to overload the circuit .
Is there a means of working out how many bulbs i can safely run on my 5amp lighting circuit.
Thanks

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You'd need your house to look like Blackpool illuminations before you overloaded the circuit ;-)

Basic physics ( P = V x I ) says that 230 volts at 5 amps provides you with 1150 watts of power.
5 amps at 240 volts = 1200 watts
Of course, if you swap your 60 watt bulbs for 3 watt LEDs, you can save money, use many more bulbs, and generate less heat.
Lighting isn't normally on a ring. Probably no reason it couldn't be.

You're unlikely to overload in a domestic residence but if you wanted to work out the load you need to add up the power if all were on at once, then divide by 230 (volts) to see how many amperes it would take. Roughly. You really need to ensure a margin extra too.

6x60=360, 7x9=56, 4x60=240. 360+56+240=656 (watts). 656÷230=2.85 amperes.

Probably ok, but get someone else to check the sums.
TC:
You're somewhat behind the times! The nominal mains voltage in the UK has been 230V, rather than 240V, since 2003. (The Government agreed to change it, in the interests of European harmonisation, in 1993, with the first step in dropping the voltage coming in 1995 and the process finally being completed 8 years later).

The supply is now nominally at 230V but permitted to rise by up to 10% (to 253V) or to fall by no more than 6% (to 216V).
I was aware that the whole of the EU was moving towards 230 volts Chris, but I'm pretty sure that if you actually measure the voltage in a UK home, you'll find it's often closer to 240 than it is to 230. The rub is in the word nominal.
...in fact, on checking, I find that the voltage in the UK is specified as being 230 volts +10% - 6%, so it could actually be as high as 253 volts!
That's what Chris said.
Lighting is normally on a ring main.
Protected by a 5 amp fuse or 6 amp breaker.
Sorry. Problems of using AB on a tiny mobile phone :-)

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