# Size of cable for SON 150w floodlight

#### lewbro

Hi all,

I am not really a novice at electrics, I am pretty clued up on terminology and domestic installation etc, however it is more of my hobby

I am installing some SON 150w floodlights, I will have 2 running.

First question, would it be better to run them on a ring? Or will a radial be ok?

Second question, they are 40m away from power source, am i right in thinking that a 1.5mm2 3 core flex cable would normally suffice for running the cables, but as its so far away it would be best to uprate the cable to a 2.5mm2 flex?

Also I would appreciate it if somebody could post the equations on how to calculate the size of cable for future references!!!!

Kind Regards

Lewis

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150W x 2 = 300W

Allowing for start-up 300W x 1.8 = 540W

540W/230V = 2.35A

Havn't got me book to hand and I'm eating me tea but you are allowed 3% VD on lighting circuits.
The formula is (mV/A/M) / 1000. I have given you the current, you know the distance so someone just needs to find the correct cable who has their book to hand. I think 1.5mm may be ok, but 2.5mm definately will be.

BTW flex will almost definately not be suitable for external wiring

I am not really a novice at electrics, I think that I am pretty clued up on terminology and domestic installation etc despite knowing absolutely nothing about the applicability of radials and ring finals or how to work out cable sizes or even knowing where to begin to look for such information.

Also I would appreciate it if somebody could post the equations on how to calculate the size of cable for future references!!!!

ricice thanks for your reply, however the lights are being installed within a hold on a small cargo ship, if I were to use solid core cable there would be quite a high chance that the vibration of the ship will damage connections. The entire ship is wired in flex!

ban-all-sheds: Thank you for your sarcasm darling, aprreciate it x

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..

well, lets pray that I know what i'm doing navigating the vessel then, and hope i'm not a novice captain. Why the hell have you assumed that I am doing the electrics? I have merely asked a question, as i'm trying to learn and understand electrics, yes i am a novice, but not to the extent that I dont know what resistance, amperage, voltage and current is etc, i do have a brain! I'm purely trying to work out what size bloody cable to order for when the electrician comes when I get in to port!

what's the point in having a forum for help when there are people like yourself purely on it to get kicks from flaming other people!!!

ok, let me see if I got this right then.....

The ships electrics are continental and running at 220v and 380v from a 30kva genset.

I=P/U 540/220= 2.25 - so the current is 2.25A

and according to Table 4.7 - Current ratings and volt drops for sheathed multi-core p.v.c.-insulated cables

I could get away with a 1.0mm2 twin core cable? As that is rated for 11amps?

the voltage drop for that size cable is 44.0mv/A/M

so 44 x 2.25 x 40 / 1000 = 3.96V

which is within the permissable drop of 4% as it equates to a drop of 1.8%

Something doesn't look right there to me, I would have thought the cable size should be bigger than that?

Any help will be appreciated thanks.

..

don't, i've just had a bloody rough trip, rolling our guts out, and i'm not really in the mood! only had 4 hours kip last night

Why the hell have you assumed that I am doing the electrics?
How about because of this:

I am installing some SON 150w floodlights
coupled with asking questions that only someone doing the work would need to know?

what's the point in having a forum for help when there are people like yourself purely on it to get kicks from flaming other people!!!
You were hardly "flamed", and any critical comments you did receive were probably because of things like this:

I am not really a novice at electrics
yes i am a novice
and

I am pretty clued up on terminology and domestic installation etc
when clearly you are not. Knowing what resistance, amperage, voltage and current are is GCSE physics stuff, and does not make you "pretty clued up" on any sort of electrical installation work.

You got the comments you did not because of what you do or do not know but because you came here spinning a line, and when that failed you tried to backpedal. If you really were pretty clued up on domestic (or any other) installation work you would already know how to work out what size cable to use.

I'm purely trying to work out what size bloody cable to order for when the electrician comes when I get in to port!
If you can contact us you can contact your electrician. Tell him what lights you want and where and let him choose the right cable.

right ok, so apparently you are not allowed to learn now, I wish i hadnt bothered

Yes I could just ring the electrician, but i'm trying to work it out and understand it all.........what's the harm in that? Seriously?

You obviously were born with a gift of instantaneously knowing everything about electrics, and haven't asked for help!

Yes I could just ring the electrician, but i'm trying to work it out and understand it all.........what's the harm in that? Seriously?

That's not what you said though, IS IT? You said " I'm purely trying to work out what size bloody cable to order for when the electrician comes"

The answers is that you order the type of cable that YOUR ELECTRICIAN TELLS YOU TO. HE is the design authority, HE carries the can if it goes wrong so he calls the tune.

Lewbro, you still don't get it, do you.

There is nothing wrong with learning, and asking questions.

But there is a great deal wrong with the following:

1) Saying "I am installing some SON 150w floodlights", asking questions completely consistent with you installing them, and then reacting badly and trying to backtrack when people "assume" that you are going to do it.

2) Saying "I am not really a novice at electrics" and then when the glaring inconsistencies between that and the questions you asked were pointed out saying "yes i am a novice".

3) Saying "I am pretty clued up on terminology and domestic installation etc" when you aren't.

You were disingenuous, and your attempt to draw attention away from that by whining about wanting to learn, and why shouldn't you learn, and what's the harm in learning, and how everyone has to learn is another failure.

I suggest you find another forum to use, and next time be honest about yourself, your knowledge, why you want to know, and the environment your questions relate to.

..

What voltage are the SONs?
Are ships not meant to be wired in some sort of fire retardant or LS&F cable?
You really need someone who knows what they are doing with ships, they are outside the scope of BS7671 which is what a lot of us here are more familiar with.

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