12v wiring

[Grehan]

I want to overhaul/extend the 12v circuitry - some sockets and things, nothing extensive. Can I use ordinary 1.0mm T+E cable? Or should I actually be thinking about heavier weight stuff to distribute current around a 10m boat. Is single core better/worse/no different to multi-core?

Thanks in advance to all you sparkies. /forums/images/graemlins/ooo.gif

 

[sailorman]

t & e a no no as it is single strand / core prone to vibration.
use "tinned" wire if you can as it doesnt degrade in the marine enviro.
as to size watch this space /forums/images/graemlins/wink.gif

 

[Grehan]

prone to vibration . . ¿que? /forums/images/graemlins/confused.gif

 

[BAtoo]

Sailorman is right; 1.0 T&E is a single wire for each segment & is designed to be used in static situation & be securely fixed.

Should use multi-strand flex, preferably tinned as pure copper will corrode & your conections get knkered

 

[Cliveshep]

If you boat inland as your profile suggests the extra expense of tinned copper wire is unnecessary as you don't have the agressive environment of coastal air/water. However, household cable, i.e. solid wire conducter, will give problems at connection points as engine vibrations can cause metal fatigue at those points leading to wires snapping in connections. Best is to use as heavy a gauge flexible wire as you can, the one sold for washing machines, i.e. 2,5mm2 3-core flex is both cheap and ideal for most 12v circuits as the additional size of conductor not only carries most 12v loads but does so without voltage drop.

I suggest you start with a new circuit straight from the battery, feed a large fuse that is always accessible, then go on to a new switch panel incorporating fuses, and wire out to lights etc from there. If you can solder your connections to this so much the better as switch panels can be notorious for faulting and of course the back of them is always buried in a helm console or similar. Oversizing your wire causes no problems, undersizing can lead to hot or burnt cables and burnt boats!

Always protect circuits with a fuse of the correct rating, that is vital. As a guide, at 230v a 2.5mm2 (square mm) conducter will carry 20amp. (Multiply volts by amps to get watts). So at 12v a 10 watt bulb consumes less than 1 amp but this will increase in proportion to the length of conductor and resistance so allow for a little more. That works for fuses, but only allow your 2.5 cable to load at 15amp max in your circuits at 12 volt or it'll get bloody hot.

 

[Grehan]

Thank you. V. clear. Will do.

 

[VicS]

As said flexible cable, preferably tinned to resist corrosion not T&E. You'll find the tinned cable at Merlin Powerstore, and others no doubt.

To avoid voltage drop it is necessary to use heavier cable than you would for 240 volt.

There is a cable size calculator HERE Read the instructions first!

There is another HERE but note the distance figure used is "there and back".
There's a link on this one to a conversion table for AWG to mm²

 

[pyrojames]

As it vibrates on a boat it will work harden and eventually crack. You should use multicore, and preferably tinned, which will increase its life. Crimp connections, don't solder, for the same vibration reasons.

 

[neale]

Do you understand the relationship with Watts, Volts and Amps and the issues with resistance and voltage drop?

Without this knowledge, you are better off leaving a re-wire to a professional, or at least gain an understanding first.

 

[VicS]

[ QUOTE ]
Do you understand the relationship with Watts, Volts and Amps and the issues with resistance and voltage drop

[/ QUOTE ]

Calculate the current for any items for which the power in watts is given from the formula
current (in amps)= watts divided by the volts (12 presumably)

The voltage drop in cables is the result of the current flowing in a conductor that has a small resistance. Even copper cables have some resistance.

volts drop = resistance of the cable X current (amps) so the greater the current the greater the volts drop.

The longer the cable the greater the resistance but that can be offset by using thicker cable which has a lower resistance than thin cable.

In 240 volt use the cable size is determined by what current it can carry safely without overheating. When you have 240 of them a few volts lost along the way is no problem but when you start with only 12 you cannot afford to loose more than a fraction of one of them. Wire a pump with cable that is too small and it just wont want to work properly. Put a cable up the mast that is too thin and your lights at the top will be dim.

 

[Grehan]

I suspect you may have passed the exam. /forums/images/graemlins/wink.gif