Freebee
Well-Known Member
I am rewiring the boat. Its 12v and I need to connect up, bilge pumps, level gauges, VHF etc etc. what size and spec of cable should I be using???
what size of cable?
- Thread starter Freebee
- Start date
ex-Gladys
Well-Known Member
Ermmmm , the right size for the device and cable run... Each of the devices you've mentioned need their own individual circuit from the bus bars. You need to look at the max current draw of each of the devices (e.g VHF on transmit) and the length of cable run from the bus bars (to the device and back), and then you can work out the gauge of wire. DC wiring at low voltage is higher current draw than mains, and voltage drop for some devices can stop them working. I generally work on no more than 3-5% voltage drop. Also can be worthwhile using tinned cable and use multi-strand cable rather than single strand, as boats "move" and flex...
Freebee
Well-Known Member
good answer but I was hoping to buy a 20 or 50 m reel of a one size fits all cable to use for all the devices, is that not possible?
benchmark
Well-Known Member
Choose your circuit voltage (12v or 24v etc), fill in expected length of cable from battery or source of power and fill in the appliance amperage as read from the sticker/label. Press calculate to see the cable size recommended.
http://www.energymatters.com.au/climate-data/cable-sizing-calculator.php
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benchmark
Well-Known Member
http://www.energymatters.com.au/climate-data/cable-sizing-calculator.php
No need to go around installing unnecessary massive large, heavy and unsightly cables if the apppliance can do with smaller ones. See cable size calculator linked above.
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Freebee
Well-Known Member
where do I find that calculator?
MoodySabre
Well-Known Member
No link.
benchmark
Well-Known Member
Link fixed in the post above.
Freebee
Well-Known Member
Thankyou
lpdsn
Well-Known Member
There's an argument that if you're completely anal about labelling the wiring you can get away with using the same colour wires for everything, but I'm not convinced. Much better to be able to identify the wires by colours. Regardless you still need to document it and draw up circuit diagrams - it's amazing how much of the little details you forget when you come back three years later to make a tweak.
There are dozens of sites selling cable so lots of competitors for you to shop around - many are aimed at the older car market but they often have stocks of tinned. Tinned is better, but doesn't come in anywhere near the same range of colours, so there's a trade off. Always use tinned if there's a risk it might get damp (or at least try).
PaulRainbow
Well-Known Member
What boat do you have, as in how long will these cables be ?
Etc etc is no good. You can't use the same cable for a windlass as a LED lamp, we need to know exactly what you have and how long the cables will be.
BabaYaga
Well-Known Member
I think you will come a long way with one reel of 2x1,5mm2 (don't use anything thinner) and another reel of 2x2,5mm2 for more power hungry or voltage drop sensitive loads. Might not cover everything, but a lot.
pvb
Well-Known Member
I reckon that's far too small for the wiring distances involved in many typical boats.
Jeepster
Well-Known Member
When working with low voltage cable there are three things to consider...The current capacity of the cable, the length of the cable and the voltage drop (and if that is going to have noticable effect on what you are running). For example, whilst something like a 4x25Watt car radio in your boat, it will seemingly run fine on twin 2.5mm2 cable, if the cable length is very short and you never crank up the volume to full but even over a couple of metres you still get a voltage drop when turning up the music to full blast...that usually results in the display dimming in time to the music and added distortion over the speakers...The simple solution is to use a higher capacity cable, even if that does mean using thicker, heavier cable...My cable run from fusebox to radio is about 2.5m and I have used flattened 42amp (4.5mm2) red and black core cable to feed it...virtually zero voltage drop, even at full volume, and very low distortion too. On the other hand, I have an Osculati DC socket (cigarette lighter socket) and twin USB socket fitting on either side of the radio housing, fed with a separate 2.5m length of the same cable. Now in this case the maximum draw for both the cigar lighter sockets (16A max each) and all four USB outputs together (5A max each) is about 42A, so you would rightly expect a noticable voltage drop using this cable, in that situation...But it is extremely unlikely that all the sockets and USB's will ever be used all at the same time, so I compromised and used the same 42A cable again. I have just ordered a 10 way, bus-bar, blade fuse holder, with screw terminals and with separate LED warning light by each fuse, to instantly show which fuse may have blown...Maximum output is 30A per fuse, so you might expect the positive input cable to the holder should be 300A cable...But as most of the outputs from the holder will only be between 5A-10A, and the run from the main battery switch is very short I can use smaller, lighter cable instead...So I will be using 70Amp (10mm2) cable for this job. The separate output cables from the fuse holder will vary in size but I certainly wouldn't use anything less than 2.5mm2 on a 5A fused output, simply so I will never have to worry about a voltage drop.
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prv
Well-Known Member
+1
I've completely rewired two boats now, and the vast majority of cable used was 1.5mm2 tinned flat twin. I would buy a 100m reel of that (will be too much, but it's typically that or multiple 20m reels running out at inconvenient times and ending up costing more) and set it up on a horizontal stick in the cabin to reel off easily as needed. Then work out individually the higher-current loads, and multi-core runs like NMEA or 3-core bilge-pump circuits, and buy the sizes and lengths required.
Different colours is fine if you're a boatyard with a rack of them, replaced as they run out. If you're doing one boat which turns out to need 4m of orange, 7m of green, 1.7m of pink-with-blue-spots, etc, then you either have a huge amount of waste or have to plan every single run in excruciating detail and then pay over the odds at per-metre prices.
Get a labelling machine - rolls royce is to print directly onto heatshrink (we use this at work) but I haven't found a machine cheap enough that I'd want to buy it with my own money. Next best is standard 6mm TZ labels run lengthways along the wire with transparent heatshrink over the top.
Unless you bodge things, you will spend more than you expect on fittings, terminals, mounting and looming stuff, and so on, besides the actual wire and electrical devices themselves. It will also take up more space than you expect.
I was very happy with each boat when I finished it, then a year or two later I'd learned enough to cringe at how much better I could do it now...
Pete
andsarkit
Well-Known Member
That solar calculator gives very conservative wire sizes for 3%voltage drop (360mV). Using it would require at least 6mm2 cable for a 25W masthead light. I think most of us with small boats would use 2.5mm2 as the larger cable would not fit the terminals.
It goes against received wisdom but my boat was wired with household single core twin and 95% is still working nearly 50 years later. The reduced copper surface area and inability for water to wick down the cable seems offset any theoretical problems with fatigue. I don't recommend this but perhaps it is best to be pragmatic rather than dogmatic.
If space for new cables is limited try looking at specialist trailer cable available in 7 to 13 cores with mixed 2.5mm2 and 1.5mm2 sizes and thinwall insulation. Unfortunately not available in tinned copper.
https://www.electricalcarservices.c...ey-sheath-7-core-21/29amps-tw07/07/p-277-2311
Ignore the current ratings as they are based on avoiding overheating rather than a sensible voltage drop.
It goes against received wisdom but my boat was wired with household single core twin and 95% is still working nearly 50 years later. The reduced copper surface area and inability for water to wick down the cable seems offset any theoretical problems with fatigue. I don't recommend this but perhaps it is best to be pragmatic rather than dogmatic.
If space for new cables is limited try looking at specialist trailer cable available in 7 to 13 cores with mixed 2.5mm2 and 1.5mm2 sizes and thinwall insulation. Unfortunately not available in tinned copper.
https://www.electricalcarservices.c...ey-sheath-7-core-21/29amps-tw07/07/p-277-2311
Ignore the current ratings as they are based on avoiding overheating rather than a sensible voltage drop.
prv
Well-Known Member
Most of us would fit modern lights drawing milliamps and string 1.5mm2 purely for physical robustness
Pete
PaulRainbow
Well-Known Member
For most installations twin core is soooooooo 1970's.
andsarkit
Well-Known Member
1969 to be exact. I think boats from the 70s had slightly better electrics.
An LED masthead light from Boatlamps is on my Christmas list.
An LED masthead light from Boatlamps is on my Christmas list.
Nigelb
Well-Known Member
Blue Sea have a nice Circuit Wizard App that is nice and easy for your phone or tablet in the yard.
