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Old 27-10-2012, 11:45   #1
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Cable Sizes: Different for +ve and -ve?

Hi All,

I am upgrading the combi on my boat and the install requires 0000 cables. The electrician seems to think that 0000 are only needed on the +ve side and we can stay with 0 or 00 on the negative (ground) side. This doesn't make a lot of sense to me. Does it make sense to the more experienced?

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Old 27-10-2012, 11:51   #2
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Re: Cable Sizes: Different for +ve and -ve?

On any circuit, the total current being supplied is exactly the same as the current going back to negative or ground or neutral. Don't think of electrons the same way you think of fuel, where the fuel flows only or mostly in one direction. Also, technically, electrons flow from negative to positive although by convention we think the opposite way.
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Old 27-10-2012, 12:11   #3
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Re: Cable Sizes: Different for +ve and -ve?

Agree with David.

In fact there are places where a light gauge would seem adequate but we frequently advise otherwise. Thousands of our customers are adding a house battery and using a Combiner100 for keeping it charged. Even though the Combiner only supplies an average of 30 amps or less we always advise a negative cable between the batteries AT LEAST AS HEAVY AS THE STARTER MOTOR CABLES.

The reason is one day the starting battery will be dead and they will use a jumper or switch to connect the positive terminals together for assisted starting. If you connect the positive terminals first a light gauge wire on the negative can be melted by battery to battery current before you can attach the negative jumper.
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Old 27-10-2012, 12:42   #4
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Re: Cable Sizes: Different for +ve and -ve?

It's time for a new electrician. This is a common mistake, but not one that should be made by any professional.
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Old 27-10-2012, 12:58   #5
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Re: Cable Sizes: Different for +ve and -ve?

OK.

Seems mistake was mine. He replaced both 0 with 0000. Problem with trying to communicate in Spanish via google translate.
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Old 27-10-2012, 13:05   #6
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Re: Cable Sizes: Different for +ve and -ve?

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Originally Posted by David M View Post
On any circuit, the total current being supplied is exactly the same as the current going back to negative or ground or neutral. Don't think of electrons the same way you think of fuel, where the fuel flows only or mostly in one direction. Also, technically, electrons flow from negative to positive although by convention we think the opposite way.

Close, but no cigar. Yes, electrons flow as you describe. However, back in the days of yesteryear (no Lone Ranger) , Ben Franklin started the confusion by declaring the direction of charge flow, positive to negative in his wax to wool experiments. Of course he was incorrect but it stuck.

I believe it was the IEEE that resolved this confusion of how electrons/current flow way back in the 50's by separating how one should compare electrons and current with a fiat that declared current flow to be from positive to negative leaving electron flow as it should be, negative to positive. Incidentally, if you look at a symbol for the common diode you will note that the arrow head points to the direction of current, not electrons.

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Old 27-10-2012, 18:04   #7
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Re: Cable Sizes: Different for +ve and -ve?

Agree with noelex, actually it is PAST time for a new electrician. Unless there is some miscommunication, and he is using the lighter cable for only PART of the ground, because for some reason that part will never see the full load?

But if he's simply saying the entire negative side should be a smaller gauge, say bye-bye.
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Old 27-10-2012, 19:55   #8
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Re: Cable Sizes: Different for +ve and -ve?

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Originally Posted by Tday01 View Post
Hi All,

I am upgrading the combi on my boat and the install requires 0000 cables. The electrician seems to think that 0000 are only needed on the +ve side and we can stay with 0 or 00 on the negative (ground) side. This doesn't make a lot of sense to me. Does it make sense to the more experienced?

Tony
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ispaf.com
Your "electrician"????? You might want to ask and make sure he is insured and also ask for some certifications. Anyone who "thinks" this is okay, well..... I'll be polite and say nothing other than; get a second opinion......
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Old 27-10-2012, 20:05   #9
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Re: Cable Sizes: Different for +ve and -ve?

Especially with DC, you can't make the wire too big. Sooner or later it will be asked to carry too many amps. I figure the gauge on my combiner to be the same as the mains comming from the batteries.
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Old 27-10-2012, 20:53   #10
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Re: Cable Sizes: Different for +ve and -ve?

Apologies to the electrician. He put the heavier duty wires on both legs. It was my misunderstanding (we were using google translate as he doesn't speak English and I dont speak Spanish).
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