Boat Wiring

[BlueLancer]

I am rewiring my boat and want to use the minimum amount of different sized wire for the lights and all the normal 12v circuits.If there are no really large demands on the load side can I do this. Do you have to have smaller size wires for light loads and larger sizes for larger loads.Can I have a larger wire size to cover all eventualities. I would appreciate your thoughts.

 

[David2452]

You can use larger cable if you wish, just make sure it's protected by the apropriate circuit breaker.

 

[ghostlymoron]

There's no reason why you shouldn't use oversizes wires as long as it will fit in the terminals of lights etc.

 

[VicS]

Generally speaking in a 12 or 24 volt system you will have to use heavier wires than you would for the same current load in a 240 volt system in order to minimize volts drop on all but short runs.

The odd volt or two lost when you have 240 of them is not important but it is, or at least can be, when you have only 12 or 24 of them to start with.

3% volts drop ( ie 0.36 volts on a 12 volt system) is usually taken as acceptable but some items of equipment are not so critical as others. Filament navigation lights with long cable runs to them are an example of where it must be taken seriously and surprisingly heavy cable becomes necessary

There are on line calculators available to help with sizing of wiring but it can be determined from a knowledge of the resistance of the various size of cable and the current load.

 

[duncan99210]

The only thing to give any pause for thought in using bigger wiring than neccessary is the cost. Thicker wire costs more, which is why you'll often find smaller sized wire used for lower current demands.

 

[pagoda]

I am rewiring my boat and want to use the minimum amount of different sized wire for the lights and all the normal 12v circuits.If there are no really large demands on the load side can I do this. Do you have to have smaller size wires for light loads and larger sizes for larger loads.Can I have a larger wire size to cover all eventualities. I would appreciate your thoughts.

If you are considering LED lamps as an alternative to incandescent bulbs, you could reduce the lighting cable size.
It's the amps you pull over the distance (and any suspect connections) which really reduce the voltage at the far end.
LED lamps don't consume much - but I have to say I don't really like the colour - and loss of cosy ambience in the saloon. If you want longevity - go for tinned copper, especially for anything going under the sole anywhere.

I've more or less worked out what wiring does what - after 3 years of study.
I have all the manuals for the equipment fitted - but no record at all of how things were wired up by previous owners. I know some of it now...

 

[prv]

I did volt-drop calculations for everything and was able to cover it all using a combination of 1.5mm and 2.5mm. I probably would have needed more had I not been using LED nav lights up the mast.

Pete

 

[Amulet]

While this is not an exact science, it is thoroughly documented. E.g., Calder gives tables of required wire gauge based on amperage and length of cable run. Hefty loads require hefty cable and the longer the run the greater the gauge needed. (You need to find a web site to do the conversion from AWG to square mm.)

Having said all that my clutzy way is:

Most electronic instruments draw so little current that the thinnest cable you can reasonably solder, crimp or whatever is enough. Lights and things can run on the kind of cable you see used in cars. For hefty loads - windlasses, fridges etc - consult the official tables. If you have a long run from a battery to a windlass, nick the cable from the nearest railway track.

I must admit that, apart from up the mast, I don't run to fully tinned cable as notionally required in marine installations. Bits of domestic wire have survived decades. However, I do worry about the possibility that a crucial cable will give up in survival conditions in the Sydney to Hobart race.......(not really, but I'd be pretty particular if I was taking on Oceans not the Walton Backwaters).

 

[BlueLancer]

I did volt-drop calculations for everything and was able to cover it all using a combination of 1.5mm and 2.5mm. I probably would have needed more had I not been using LED nav lights up the mast.

Pete

Now that sound more like it. 2 gauges covering most thing,s that's what I am looking to achieve.Reading the books I would need if following the guidance they give about 10 different gauges

 

[BlueLancer]

While this is not an exact science, it is thoroughly documented. E.g., Calder gives tables of required wire gauge based on amperage and length of cable run. Hefty loads require hefty cable and the longer the run the greater the gauge needed. (You need to find a web site to do the conversion from AWG to square mm.)

I have the Calder Bible and the Book by Mr Wing and they provide to much information to the point of doing my head in. Hence the question

 

[Billjratt]

It may seem unlikely at the moment, but there may be a reason to change out LEDs for something hungrier in the future so do not pare sizes down to a minimum or you will have a real pain to deal with...
It's reasonable to run a pair of 56-strand wires down each side of the boat and then 'T' the lights off them with 14-strand (used to be .0076" per strand - you convert - I still use old money)

 

[William_H]

Wire size

It seems to me that physical robustness leads to long life for wiring. So there is nothing wrong with using heavy wire. (As suits the terminals fittings etc.) I would certainly recommend LEDs for lights making wire gauge unimportant. good luck olewill

 

[prv]

It may seem unlikely at the moment, but there may be a reason to change out LEDs for something hungrier in the future

Seems highly unlikely to me - better technology may come along, but energy use is always going to be important on a boat. Hence I can't see any future system going back to the power demands of the Victorian idea of white-hot twists of wire.

If it does, I'll pull new cable. I've already proven I can do it once.

Pete

 

[Tintin]

1.5mm and 2.5mm are what I use, except for heavy duty stuff - a coil of each will see you right.