1.5mm or 2.5mm wire?

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jimmyk

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I am planning a partial retire. Need to tidy up bilge pump. Solar panel. Charger. Radio and various bits and pieces. None have a massive load. So asking if I should use 1.5 mm or 2.5 mm tinned wire. Any advice would be welcome. Thanks
 
jimmyk said:
I am planning a partial retire. Need to tidy up bilge pump. Solar panel. Charger. Radio and various bits and pieces. None have a massive load. So asking if I should use 1.5 mm or 2.5 mm tinned wire. Any advice would be welcome. Thanks
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Generally the thicker the better, fit the right size breakers or fuses.
 
I did mine more like a house. 1.5 for all the led light circuits and 2.5 for most of the other stuff except pumps,motors and stereo. Runs from battery bank to the control panels is 6mm.
 
Also please. I have no big fuses on the battery cables. The house battery is 110 amp gel battery. The starter battery is 90 amp lead acid. What size fuses should I put. And where would be the best place to put them please
 
jimmyk said:
Also please. I have no big fuses on the battery cables. The house battery is 110 amp gel battery. The starter battery is 90 amp lead acid. What size fuses should I put. And where would be the best place to put them please
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I was told not to put fuses in those runs. I might have been given duff gen though.
 
Fuses are to protect, the question is protect what.
For cables you place a fuse at the power source or anywhere that the cable capacity reduces (as in smaller wires from a distribution panel). For equipment fuses are usually part of the kit.
Now, with alternators theres a problem, disconnecting it while its running can break it so care should be taken.
Ignoring the alternator for now then the run from the battery is vulnerable to short circuits that will start a fire, so a fuse at the battery on that cable is sensible, or make darned sure the cable is well protected.
Then at the distribution panel there should be smaller protection for the circuits both inside and to your boat equipment.
Back to the alternator, you probably dont want to it just because some cabling get damaged, so a wire from the alternator to the battery rather than the distribution panel makes sense, fuse it to prevent fire or again protect it.
There are regulations and codes of practice for commercial boats ,but private is more up to the owner, what gives you peace of mind, fuse or protect, risk a dead alternator vs a fire.
 
OK, from a proffesional point of view, let's assume an average 1500 GPH (rated) 7a @ 12v Bilge pump and a round trip Battery + to battery - of 30 feet, 1.5mm2, (16AWG, 2.5 kcmil), will give a voltage drop of 7% which is well under the standard required for such a component. VHF (assuming again that by radio you mean VHF and not audio) requires a standard of 3% so same distance would need bigger cable than 2.5mm2, in fact 12AWG which is just over 3mm2. From my answer using assumptions which are unlikely to correspond with your actuality you will deduce that as you have not given any of the distances or current draw for your required devices that both mine and the other answers so far are pretty meaningless until we have that information. Oh, by the way, enjoy your partial retirement.
 
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David2452 said:
OK, from a proffesional point of view, let's assume an average 1500 GPH (rated) 7a @ 12v Bilge pump and a round trip Battery + to battery - of 30 feet, 1.5mm2, (16AWG, 2.5 kcmil), will give a voltage drop of 7% which is well under the standard required for such a component. VHF (assuming again that by radio you mean VHF and not audio) requires a standard of 3% so same distance would need bigger cable than 2.5mm2, in fact 12AWG which is just over 3mm2. From my answer using assumptions which are unlikely to correspond with your actuality you will deduce that as you have not given any of the distances or current draw for your required devices that both mine and the other answers so far are pretty meaningless until we have that information. Oh, by the way, enjoy your partial retirement.
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Ha ha. Very good. Re read my post. If only.
The wire runs are pretty short in all honesty. Vhf and fm radio less than a metre. Bilge pump no more than 2 metres. Solar panel bit longer at 3 metres. The main battery cables, longest one is about 60 cm. Others are much shorter
 
VicS said:
If you are going to laugh at a professional like David I'd think you can wave good bye to any future help or advice from him!

However to walk you through whats involved

Take a small bilge pump with a current consumption of 7amps ....
Assume a max acceptable volts drop of 3% ..........
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Any substance to these assumptions?
The smallest Rule pumps only need a 2.5A fuse.
If you want max performance, obviously max volts is a good guess, but 3% seems like a finger in the air to me.
 
VicS said:
If you are going to laugh at a professional like David I'd think you can wave good bye to any future help or advice from him!

However to walk you through whats involved

Take a small bilge pump with a current consumption of 7amps and wiring 2 metres long ....... that's 2 metres positive and 2 metres negative making a total wire length of 4 metres.

Assume a max acceptable volts drop of 3% ... 3% of 12 volts is 0.36volts The resistance that will give this volts drop at 7 amps is 0.36/ 7 = 0.051 ohms. ( lets call it 0.05) ... in 4metres remember.

This will be equivalent to a resistance of 0.05 x 1000 / 4 = 12.5 ohms/ 1000m ( lets call that 13 ohms/1000m))

Now if you refer to a table of wire resistances ( eg http://www.engineeringtoolbox.com/wire-gauges-d_419.html you will find that AWG 16 ( 1.3mm²) has a resistance of 13 ohms/1000m This means that for a small bilge pump, wih a current consumption of no more than 7A, AWG 16 will just but only just) be heavy enough if the cable is no more than 2metres long. So 1.5mm², for this example, heavy enough by a very small margin.

If your pump takes more than 7 amps rework the calculation for the actual current consumption.


Now you can follow the same procedure to determine the wiring size required for your other pieces of equipment.
You may have to interpolate between the figures in the table but at the end round up to the next available size.
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I think you will find the op's "ha ha" is about the "rewire" becoming "retire" in the op, not a laugh at David whom I know we all respect.
 
VicS said:
If you are going to laugh at a professional like David I'd think you can wave good bye to any future help or advice from him!

However to walk you through whats involved

Take a small bilge pump with a current consumption of 7amps and wiring 2 metres long ....... that's 2 metres positive and 2 metres negative making a total wire length of 4 metres.

Assume a max acceptable volts drop of 3% ... 3% of 12 volts is 0.36volts The resistance that will give this volts drop at 7 amps is 0.36/ 7 = 0.051 ohms. ( lets call it 0.05) ... in 4metres remember.

This will be equivalent to a resistance of 0.05 x 1000 / 4 = 12.5 ohms/ 1000m ( lets call that 13 ohms/1000m))

Now if you refer to a table of wire resistances ( eg http://www.engineeringtoolbox.com/wire-gauges-d_419.html you will find that AWG 16 ( 1.3mm²) has a resistance of 13 ohms/1000m This means that for a small bilge pump, wih a current consumption of no more than 7A, AWG 16 will just but only just) be heavy enough if the cable is no more than 2metres long. So 1.5mm², for this example, heavy enough by a very small margin.

If your pump takes more than 7 amps rework the calculation for the actual current consumption.


Now you can follow the same procedure to determine the wiring size required for your other pieces of equipment.
You may have to interpolate between the figures in the table but at the end round up to the next available size.
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I was laughing at his joke. I suggest you read the post
 
The steady state current consumption for the pump is only part of the story. There is a substantial surge on startup as there is with any motor. My rule of thumb for 12V wiring is to aim for 0.5V drop or less.
 
David2452 said:
OK, from a proffesional point of view, let's assume an average 1500 GPH (rated) 7a @ 12v Bilge pump and a round trip Battery + to battery - of 30 feet, 1.5mm2, (16AWG, 2.5 kcmil), will give a voltage drop of 7% which is well under the standard required for such a component. VHF (assuming again that by radio you mean VHF and not audio) requires a standard of 3% so same distance would need bigger cable than 2.5mm2, in fact 12AWG which is just over 3mm2. From my answer using assumptions which are unlikely to correspond with your actuality you will deduce that as you have not given any of the distances or current draw for your required devices that both mine and the other answers so far are pretty meaningless until we have that information. Oh, by the way, enjoy your partial retirement.
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Except maybe the post that gives the OP and readers a tool to work it out.

Give a man a fish and you feed him for a day, teach him to fish and he can feed himself.
 
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