# What considerations do I need when wiring a string of light bulbs in parallel?

I want to build a hollywood style mirror light for my wife (as pictured below). I'd like it to be powered by mains electricity (230v where we live in the UK), but I understand the bulbs will take mains voltage so any exposed wiring can be dangerous. What considerations should I take about wiring? Should I calculate an appropriate fuse for aproximately 15 lightbulbs?

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I am a commercial electrician in the US and I'm not very familiar with UK standards or code, but I should be able to help a little.

From what I understand, a typical household runs lighting on a 5A fused circuit. Watts = Volts*Amps = 230*5 = 1150 Watts maximum total on the lighting circuit. It the US we us a maximum of 80% of the rated load, which would equate to 920 Watts. This allows for voltage spikes when first turning on and off the lights, random power surges, etc. Keep in mind that this rating is for the entire circuit, so if there are any other lights, receptacles, or appliances attached to the same circuit, you would have to subtract those to figure out how much power you have left to use for your project.

The wattage of each light bulb is going to be your biggest factor. If each bulb was 100 watts, multiplying that by 15, you are 1500 watts, 580 watts over your 100% fuse limit, and that's if there is nothing else at all on the same circuit (unlikely). If you used 40 watt bulbs, you are at a total 0f 600 watts, which leaves you with room to spare, and would probably be plenty of light for a vanity mirror like what you have in mind.

As far as the actual construction goes, running mains power through a wood frame to your lampholders with multiple splices isn't the safest diy project, but it can be done safely if you know what you're doing. Maybe somebody else can comment on that issue.

I would use low voltage LED lighting if it were my project. It's safer and uses much less power, but would probably be more expensive to put together and it would involve some more design considerations.

Good luck on your project and keep us posted.

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one thing to add maybe to this (more comprehensive answer) add a label of the max wattage for the bulbs on the finished project, so the guy who gets it later knows what is safe for it. – ratchet freak Apr 21 '14 at 20:55
In the UK, modern 5A lighting circuits are fixed wiring in the ceiling. A DIY vanity mirror is more likely to be plugged into a general BS1363 13A socket on a 32A circuit. In this case the plug must always be fitted with an appropriate fuse (e.g. 2A). – RedGrittyBrick Apr 21 '14 at 22:33

to get the needed amp rating for the wiring and fuse you take the wattage of the bulbs divide by the voltage and multiply by number of bulbs.

so 15 75W bulbs means 75W/230V*15 ~ 5 amps. this is much less than would need a dedicated circuit. (it's the same as a 1125W appliance).

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