shed lighting and cable rating

shortaii · Aug 5, 2013

Hey guys, studying to be a sparky and stuck on a question. The question is to install 2x65W fluorescent lights (single unit) in a garden shed which is attached to the side of the house, with a cable length of about 8 meters to light from the CU at 230V supply. Is this just 2x65W=130 130/230= Ib of 0.57A then In/correction factors that apply or am I missing something? Secondly what cable would be best to use, I know I would have to do the right calcs to find the right size and then find the volt drop of no more than 3%. Any help would be brilliant, cheers in advance.

Richard Burns · Aug 5, 2013

Not sure what level you are at so this may not apply but fluorescent lights can have a power factor of as low as 0.8 so this would be used as a divisor of the Ib, if you have been given a power factor use that.
Consider volt drop first for cable size as this can be the overrriding factor (probably not for 8m).
Also consider the external influences for the cable to select a suitable cable type.
Remember the minimum cable size for lighting fixed wiring is 1mm².

Clive P · Aug 5, 2013

Hi,

As it is your first post , I will give you some pointers. When asking a question it is always a good idea to supply as much information as you can, ie,

1. Type of supply.
2. Ze reading.
3. Type of CU in place and type of OCPD's.
4. Is there an RCD protecting this.
5. Will there be any future additions to the 'shed' which will help determine the size of supply cable required.

There are many more , but this will give you something to think about.

As for the loading for the light, you need to multiply this by 1.8. Do you know the reason for this?

How do you think the cable should be run? If you put forward information people are more inclined to help; it's the way to learn. If we tell you the answer you won't have learnt anything.

Regards.

Guitarist · Aug 5, 2013

So this isn't a job you're doing at home, and want advice on how to go about it?

shortaii · Aug 5, 2013

Thanks for the pointers Clive, in the question I have not been given all the variables. I was only given the ones I wrote in my original post an I kind of fill in the rest. I am assuming it is a single phase 230V supply so it would be 2 x 65w x 1.8/230V = 1.017A I think this is right

I am assuming the 1.8 is for MD. As for the run of the cable, possibly in the wall or clipped to it then straight through the wall into the shed and up to the light fixture. No additions to the installation. Thanks

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