16mm square twin cable?

Just to add to the above... i use drivesafes 6 b&s cable on my boat in a 6m length, i run it from the dual circuit switch through to the fuse box / distribution point. I run a 600w depth sounder and gps unit, a dvd / stereo / cd unit running 6 speakers, a 27mhz radio, the lighting, bilge pump, accessory sockets etc etc (12 fuses direct and 6 ignition switched....)

with most things running (and to be fair they dont pull that much current) i get very little voltage drop probably less than 0.2v which i can live with.. i probably drop a fair bit of that across the 50a breaker thats inline too..

Steve

You might find this site useful. It allows you to easily determine voltage drop for any run length, maximum current draw and cable size. [Remember that the run length includes the earth return.]

Voltage Drop and Cable Size Calculator

Voltage drop equals (cable length (in metres) X current (in amps) X 0.017) divided by cable CROSS SECTION in mm.sq.

example:-
6m x 35A x 0.017 / 10mm2 = 0.36v drop

Note: These are calculated using a common ground - chassis

Quote:

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Originally Posted by drivesafe

Back to the 6mm Auto, it’s only 4,5mm2 and if you tried to pull 50 amps down just 0.5 metres of this cable, you would get around a 2 to 3 volt drop and with in just a few minutes, the cable would get so hot you could not hold it without getting burnt.

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4.5mm2 cable should be able to handle 50 amps easy. The cable you use must be garbage. I have 2.5mm2 running over 32 amps (at 12 volts), with no problems, and I would expect I would get close to 50 amps on that without problem. It is a high quality, multi strand STI cable, with 110 degree insulation, so the 4.5mm2 stuff you are using must be 7 strand cheapy with normal (70 degree) insulation. Oils ain't oils as they say...

Quote:

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Originally Posted by bacicat2000

4.5mm2 cable should be able to handle 50 amps easy. The cable you use must be garbage. I have 2.5mm2 running over 32 amps (at 12 volts), with no problems, and I would expect I would get close to 50 amps on that without problem. It is a high quality, multi strand STI cable, with 110 degree insulation, so the 4.5mm2 stuff you are using must be 7 strand cheapy with normal (70 degree) insulation. Oils ain't oils as they say...

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The cable Drivesafe sells is good quality multi-strand cable.

Quote:

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Originally Posted by bacicat2000

4.5mm2 cable should be able to handle 50 amps easy. The cable you use must be garbage. I have 2.5mm2 running over 32 amps (at 12 volts), with no problems, and I would expect I would get close to 50 amps on that without problem. It is a high quality, multi strand STI cable, with 110 degree insulation, so the 4.5mm2 stuff you are using must be 7 strand cheapy with normal (70 degree) insulation. Oils ain't oils as they say...

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Hi bacicat, the 6mm auto cable I supply is 65/.30, 4.59mm2, 75 degree premium AUSTRALIAN MADE automotive cable.

As to the number of strands, this means absolutely nothing as far as current carrying capacity and heat handling goes. The square rating of cable is based on the total amount of copper in a cross sectional area on the cable.

So whether you have a single 4.59mm2 rod bar of copper, or high grade 4.59mm2 audio cable with a few hundred thin strands, the current carrying capacity is the same.

The advantage of more but thinner strands just means the cable is more flexible.

Furthermore, there is no way you could get 32 amps down 5mm Auto cable without having a huge voltage drop and regardless of the tolerable operating temperature, 75 verses 110, the cable will still heat to the same temperature, the higher rating just means it will need to get to a higher temperature before it start to melt.

Your 110 degree cable will be just as hot to handle at 75 degrees as the 75 degree cable will be.

Quote:

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Originally Posted by drivesafe

As to the number of strands, this means absolutely nothing as far as current carrying capacity and heat handling goes. The square rating of cable is based on the total amount of copper in a cross sectional area on the cable.

...

The advantage of more but thinner strands just means the cable is more flexible.

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For DC this is correct. But on a slight tangent, I was discussing the issue of surface area of cable the other day with one of the electrical engineers here.
Google found this:
Current capacity of multi-strand versus single-strand

Not wanting to disagree with you on technicalities Tim as sparklers really is your game
BUT
Theoretically (physics as opposed to real life) electrons can only flow along the surface of a conductor. Theoretically multiple strands offer much greater surface area per cross section than a solid conductor. This reduces the effective electron density when current flows, which theoretically reduces the transmission losses (think friction) of the conductor.

Im not sure how real world relevant this is but it would be easier enough to jam 100A down a 5mm copper bar vs some equivalent multistrand and measure the resistance / temperature difference?

S

Quote:

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Originally Posted by roverrescue

Not wanting to disagree with you on technicalities Tim as sparklers really is your game
BUT
Theoretically (physics as opposed to real life) electrons can only flow along the surface of a conductor. Theoretically multiple strands offer much greater surface area per cross section than a solid conductor. This reduces the effective electron density when current flows, which theoretically reduces the transmission losses (think friction) of the conductor.

Im not sure how real world relevant this is but it would be easier enough to jam 100A down a 5mm copper bar vs some equivalent multistrand and measure the resistance / temperature difference?

S

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See the link I posted above. Seems to only be significant for high frequency AC.

Well there you go, my theory knowledge is flawed, only get the electron "skin" effect with AC.
Apologies Tim ;)

Can I go home now, I have learnt something new!

S