Thinnest cable for 5 watt masthead led nav bulbs?

[fredrussell]

I’m redoing masthead wiring. Mast is stepped. It’s a z spars mast and has a small (25mm or so) plastic conduit for wiring. There’s currently vhf, N2k wind, steaming light, and a 3 core cable for tricolour and all round white.

I’ve removed the corroded 3 core cable leaving a mousing line in its place. Space is tight in that conduit and I’d like to replace the old 3 core cable with the smallest possible cable, preferably tinned. Bulbs are LED 3 watts or so. Could anyone advise as to what is the smallest (mm2) cable I can use safely. If it’s tinned, all the better and hopefully available in a 3 core SLIM cable. I’ve typed “3 core cable” into eBay but unsurprisingly that yields loads of 240v household flex.

 

[simonfraser]

structual strenght more important i recon
unlikely to burn out the wire with a 3W LED bulb, if the run is v long will have some voltage loss
can check that bit out using on line wire calculator

 

[Tranona]

12voltplanet.co.uk/3-core-thin-wall-auto-cable-3-x-16-5-amp.html

 

[yotter]

I have just done the same, I replaced working 2.5mm 3 core (not tinned) with 1.5mm 3 core tinned, I used Oceanflex, very available online from many suppliers. This is for LED.

 

[LittleSister]

Could anyone advise as to what is the smallest (mm2) cable I can use safely.

Just to be clear, it won't be 'unsafe' to use a thinner cable (at least any cable you would realistically use), but the thinner the cable the greater the voltage drop before it gets to the lamp. I doubt that would be a problem with the 1.5mm cable recommended above but others will be better able to advise.

You could potentially reduce further the size of the cable from 3 core to 2 core by having a nav light switch that reverses the polarity of the two cables reversed for one lamp compared to the other, and diodes at the masthead to direct the current through the relevant lamp. If you're interested in that possibility, then ask here and detai8ls can be explained.

 

[PaulRainbow]

12voltplanet.co.uk/3-core-thin-wall-auto-cable-3-x-16-5-amp.html

That's not tinned though.

 

[PaulRainbow]

1.5mm Oceanflex is a good choice.

12V planet often get suggested on this forum, but they are expensive. For example, 1.5mm 3 core is £2.88 per metre, a really quick Goggle search comes up with £1.57 per metre (might be cheaper, it was a quick look) Oceanflex Tinned 3 Core Round Cable 1.5mm 3core CM03/04 - Marine Electricals

 

[Plum]

I’m redoing masthead wiring. Mast is stepped. It’s a z spars mast and has a small (25mm or so) plastic conduit for wiring. There’s currently vhf, N2k wind, steaming light, and a 3 core cable for tricolour and all round white.

I’ve removed the corroded 3 core cable leaving a mousing line in its place. Space is tight in that conduit and I’d like to replace the old 3 core cable with the smallest possible cable, preferably tinned. Bulbs are LED 3 watts or so. Could anyone advise as to what is the smallest (mm2) cable I can use safely. If it’s tinned, all the better and hopefully available in a 3 core SLIM cable. I’ve typed “3 core cable” into eBay but unsurprisingly that yields loads of 240v household flex.

I would use this Oceanflex 3 Core Tinned Thin Wall Cable - 3 x 21A (1.5mm²)

Edit: sorry Paul, did not see you had already said this

 

[lustyd]

Bulbs are LED 3 watts or so

Currently fitted bulbs. If there's any chance at all someone may put in a traditional bulb I'd plan for that. LED bulbs are easy to find in civilised areas but will you sail to less well stocked locations? Even if you fuse it, someone might swap out the fuse and burn out the cables in the mast while trying to get a traditional bulb working.
That said, I think traditional bulbs are 20W anyway (so 3-4A total on the common negative wire) so the choice might be the same but I thought it worth raising

 

[fredrussell]

Currently fitted bulbs…

It’s a good point, and one I hadn’t considered so cheers. I’ll put some low-as-possible rated fuses between mast and control panel.

The Oceanflex 1.5mm x3 is a good call - thanks to all.

 

[Alex_Blackwood]

It’s a good point, and one I hadn’t considered so cheers. I’ll put some low-as-possible rated fuses between mast and control panel.

The Oceanflex 1.5mm x3 is a good call - thanks to all.

The 1.5mm cable is rated at 21 amps so they may have to fit a rather high amperage fuse.

 

[PaulRainbow]

It’s a good point, and one I hadn’t considered so cheers. I’ll put some low-as-possible rated fuses between mast and control panel.

The Oceanflex 1.5mm x3 is a good call - thanks to all.

Just use 5a fuses, good for either and the cable is well up to the job at 21a.

 

[B27]

There are LED lights and then there are other LED lights.
Mine are 10 to 28V jobs, so it doesn't matter if the cable has a little resistive drop, at 10V it will draw 330mA for 3W.
To drop a volt in each direction would be about 3 ohms!
You could use a very thin cable and electrically it would be fine, but for robustness I'd suggest not going to extremes.
American Wire Gauge Chart and AWG Electrical Current Load Limits table with ampacities, wire sizes, skin depth frequencies and wire breaking strength

Some cable sold for alarm systems is good value, well plated and easy to handle.
The key thing is protecting the ends and bends.
Also some cable is not UV-proof, you could heat-shrink any exposed bits though.

 

[Sandy]

Oceanflex Tinned 3 Core Round Cable 1.5mm 3core CM03/04 - Marine Electricals

Thanks for the link @PaulRainbow they are en route to the boat.

 

[Sparkylarks]

Just remember that the important factor for the cable size is the fuse, if you reduce the cable size, you might need to reduce the fuse.
I'd make sure it is 15A or less for those cables.

Probably unlikely to be an issue with bulbs,

 

[Alan S]

The 1.5mm cable is rated at 21 amps so they may have to fit a rather high amperage fuse.

Qué?

 

[Alex_Blackwood]

Qué?

Alex_Blackwood said:
The 1.5mm cable is rated at 21 amps so they may have to fit a rather high amperage fuse.

Yes, sorry, I was actually referring to post #9 and someone putting in a fuse that would burn out the cable.

 

[Alan S]

I wonder what fuse would burn out a 1.5mm² cable?

 

[Alex_Blackwood]

I wonder what fuse would burn out a 1.5mm² cable?

A big one

 

[Alan S]

Yes indeed, much bigger than anyone with any electrical knowledge would consider using for a masthead light.