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Old 20 July 2011, 06:54   #1
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-ve wiring

Hi

I have a positive distribution block in my console but no negative. There is a navlight on my boat with a switch on the console.

The wiring for the nav light goes something like this:

Wire from (fused) positive block to switch. Switch goes back to light and then to battery (-ve).

I am installing a radio in the console, obviously I have positive power from the block but no way to complete the circuit back to the battery on the -ve side. Can I run a single cable back to the battery -ve terminal and attach all the negative cables from devices such as radio/chartplotter?

Thanks
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Old 20 July 2011, 07:39   #2
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Something like this? The =ve busbar has individual fuses for each terminal and the radio has its own inline fuse. I take it I could go straight back to the battery without the -ve bar as I only have one piece of equipment (the radio) installed at the moment.

Thanks.

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Old 20 July 2011, 07:51   #3
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Sounds good to me
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Old 20 July 2011, 08:08   #4
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It's annoying that the people that installed the engine and the nav light didn't put a negative return feed in the console, I will have to run another cable.

I take it 1.5mm^2 tinned thinwall cable rated at 21a will do the job? For now all it will be returning is electricity from the radio.
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Old 20 July 2011, 08:11   #5
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If you go to the trouble of laying in a negative cable, make it a reasonable size so it's future proof.
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Old 20 July 2011, 08:16   #6
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How many amps would you say for a chartplotter and a vhf? That's the most it's ever going to need to handle.
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Old 20 July 2011, 08:22   #7
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Quote:
Originally Posted by maxhar View Post
How many amps would you say for a chartplotter and a vhf? That's the most it's ever going to need to handle.
Dunno, look in the manuals. A VHF transmitting on 25watts is going to be 2.5ampsish for starters. If your cable run is long, there will be a voltage drop due to its resistance.
Fatter cable = less resistance.
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Old 20 July 2011, 08:25   #8
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The 21 amp thinwall cable should be fine then.
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Old 20 July 2011, 08:27   #9
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Gut feel tells me I'd want a 3mm or 5mm cable ready for any future goodies. No point scrimping especially where safety gear is concerned. It can be calculated but you'd need to know the length of wire needed and the current draw. Don't forget that the length needs to be both the pos and neg distances added together.
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Old 20 July 2011, 08:28   #10
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The 21 amp thinwall cable should be fine then.
Thin wall? Are you likely to nip it, walk on it, trap it, drag it through a hole etc...?
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