Suitable cable size for 200m length

[curtle101]

Hi All,

A query for all of the romantics out there and any help you could give with this would be really appreciated.

For a friend's wedding, we want to string up 5 sets of fairy lights, in series, which cover a total approximate distance of 200m away from the socket. i.e. The furthest light will need to plug in about 200m away, the nearest will be about 50m away from the mains socket.

Each lighting set is Low Voltgae (24V, 28.8W) and suitable for outdoor use.

What is the best cable to use? As far as I can work out Arctic Flex is best for this purpose but I'm trying to work out the best diameter (e.g. 2.5mm etc) as not sure what the total voltage drop would be. The overall load from the lights is fairly small but the distance I think is going to cause issues.

Any help you could give would be greatly appreciated. I've tried to upload a diagram to make my explanation clearer but leave any questions and I'll answer them.

Thanks,

Jon.

 

[holmslaw]

..

 

[plugwash]

You have a total load on the mains voltage side of about 0.06A

You are out by an order of magnitude, total current is more like 0.6A not that that changes things much, even at that current 1.5mm arctic would be easilly sufficiant to carry the current with acceptable volt drop.

RCD protection is essential partly because it's outside and partly because you need it to ensure tripping on earth faults.

If these lights are 24V where are the transformers going? are the transformers waterproof and designed to be located outside? if not you will need to find suitable enclosures to house them.

 

[holmslaw]

..

 

[westie101]

We have TX ratio of approx 10-1, so 28.8Watts at 24V becomes 2.88 Watts at 240V, 2.88 x 5 = 14.4 Watts.

Er you can convert current using that formula but not power

 

[holmslaw]

..

 

[curtle101]

Hi all,

Thanks for all of your reponses. I'm glad the plan works.

Please could you confirm whether I could use 1.5mm Arctic flex or whether I would have to buy the 2.5mm Arctic flex. The comments seem to be debating over an order of magnitude (0.6A vs 0.06A) but would the higher value (0.6A) require me buying the 2.5mm flex which is more expensive?

If not, then issue solved and I'll start finding the cheapest supplier for 1.5mm flex.

Thanks again,

Jon.

 

[westie101]

Yes. The total power input/output from a transformer is fixed (well it isn't if you want to take account of transformer losses) voltage & current are different on either side

 

[electronicsuk]

We have TX ratio of approx 10-1, so 28.8Watts at 24V becomes 2.88 Watts at 240V, 2.88 x 5 = 14.4 Watts.

Er you can convert current using that formula but not power

So, you're saying a TX ratio applies to the volts and to the current, but not to the power, which is a component of volts and current.

This is very basic electrical theory. Losses excepted, primary watts = secondary watts. The power does NOT change across the transformer. If your theory were correct then we'd all be running ELV lighting, as we'd be getting watts for nothing on the secondary of the transformer!

 

[ban-all-sheds]

We have TX ratio of approx 10-1, so 28.8Watts at 24V becomes 2.88 Watts at 240V, 2.88 x 5 = 14.4 Watts.

Er you can convert current using that formula but not power

So, you're saying a TX ratio applies to the volts and to the current, but not to the power, which is a component of volts and current.

A transformer ratio can apply to voltage and current.

28.8W at 24V is 10x the current of 28.8W at 240V - there's your 10:1 ratio.


REQUEST TO ALL READERS:

Suggestions please on what to do with guessers and chancers who give stupid advice.

 

[electronicsuk]

Please could you confirm whether I could use 1.5mm Arctic flex or whether I would have to buy the 2.5mm Arctic flex. The comments seem to be debating over an order of magnitude (0.6A vs 0.06A) but would the higher value (0.6A) require me buying the 2.5mm flex which is more expensive?

If you're distributing 230v with the transformers located at each branch then yes, 1.5mmsq will be fine.

 

[curtle101]

Wow, the speed of this forum is brilliant!

Thanks again and particularly for concurring on the cable size!

Cheers,

Jon.

 

[ricicle]

We have TX ratio of approx 10-1, so 28.8Watts at 24V becomes 2.88 Watts at 240V, 2.88 x 5 = 14.4 Watts.

So mains current (I = W ÷ V) is 14.4 ÷ 240 = 0.06 Amps

And I thought you were cleverer than that - this is very basic theory

 

[Taylortwocities]

Too much jungle juice again.

And its been done before.
//www.diynot.com/forums/viewtopic.php?p=1785994#1785994
A lesson in formulae transposition, once you've finished with Bubbles.

Again

Untitled

• Taylortwocities
• 1 Nov 2010
• 3

 

[curtle101]

Just for my own understanding, could someone please write out the calculations used to work it out as 0.6A and the voltage drop associated with that. It's apparently not the calculations used by Holmslaw but I'm interested to know how it's calculated and how you calculate that the 1.5mm arctic flex would be suitable. All I know is that it has an amp rating of 15A and a resistance of about 13ohms per km @20degreesC.

I just find it interesting. I'm an engineer just not an electrical engineer!