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Old 21-05-2015, 18:32   #1
alx
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12V Negative - Shared or Per-Circuit?

I've been working on rewiring my J/30. The factory wiring had a single bundle of primary wires wrapped in electrical tape, running from the panel on starboard aft to the transom, across to the port side, and then forward up to the bow. Individual wires would exit the bundle to their loads along the way.

Critically, there was a single negative wire in the whole bundle. Every load had a negative spliced onto this wire.

For my rewire, I am considering using duplex wire, resulting in a separate negative connection for each circuit (terminated on a negative bus next to my fuse boxes).

So far I can see these pros/cons for the per-circuit approach:

PRO: No single point of failure for all circuits (except for connection back to battery of course)
PRO: Duplex wire has double insulation, better protection against chafe, moisture intrusion, etc.
PRO: Each circuit is only as long as it needs to be.
PRO: No need to strip wires along the way - connections only made at ends.

CON: Bulkier and heavier wiring bundles.
CON: More expensive to implement.

Is there a reason I might be overlooking why either approach is preferred?
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Old 21-05-2015, 18:53   #2
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Re: 12V Negative - Shared or Per-Circuit?

A single negative is a common concept - i.e. that's how cars are wired.

But, unless that single negative was a pretty dang big guage of wire, it was likely overloaded.

I'd vote for duplex. It's what I've done when rewiring most of my boat.
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Old 21-05-2015, 18:56   #3
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Re: 12V Negative - Shared or Per-Circuit?

I'm with you, I have used separate(dual core) grounds for each circuit.
Too much hassle tapping into a heavier ground wire, and introducing single point of failure!
Although, the ground wire for the windlass provides a good neutral backbone.
A b!T@h to tap and seal though.

Curious what system you are using for charging?
Manual 1,2,both or relay, or battery combiner?
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Old 21-05-2015, 19:49   #4
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Re: 12V Negative - Shared or Per-Circuit?

Saving money is the reason to use just one ground cable. Might as well have a metal boat.
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Old 22-05-2015, 07:55   #5
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Re: 12V Negative - Shared or Per-Circuit?

Separate your loads into critical and non critical. Lights and motors can share a (correctly sized) common negative. Instruments, radios, audio gear, radar etc., can all benefit by having dedicated negative connections.
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Old 22-05-2015, 08:24   #6
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Re: 12V Negative - Shared or Per-Circuit?

Another way is Buss bars, you can locate two or three neg buss bars and connect them with a big gauge wire.
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Old 22-05-2015, 08:38   #7
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Re: 12V Negative - Shared or Per-Circuit?

^^ Yep, what A64pilot said +1
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Old 22-05-2015, 08:49   #8
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Re: 12V Negative - Shared or Per-Circuit?

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^^ Yep, what A64pilot said +1
Except they are called bus bars.
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Old 22-05-2015, 08:54   #9
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Re: 12V Negative - Shared or Per-Circuit?

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Except they are called bus bars.
Or busbar or bussbar or at least according to wikipedia
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Old 22-05-2015, 09:13   #10
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Re: 12V Negative - Shared or Per-Circuit?

Quote:
Originally Posted by Andina Marie View Post
Separate your loads into critical and non critical. Lights and motors can share a (correctly sized) common negative. Instruments, radios, audio gear, radar etc., can all benefit by having dedicated negative connections.
And let's not neglect "individually fused/circuit breakered". It's the royal road to solving outages.
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Old 22-05-2015, 09:17   #11
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Re: 12V Negative - Shared or Per-Circuit?

Everything I have seen and done has been with bus bars (no matter how it is spelled). I makes tracing any faults much easier. Proper sizing is critical.
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Old 22-05-2015, 09:22   #12
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Re: 12V Negative - Shared or Per-Circuit?

Quote:
Originally Posted by a64pilot View Post
Another way is Buss bars, you can locate two or three neg buss bars and connect them with a big gauge wire.
Exactly.. Buss bars are definitely the way to go. Good, clean, and safe way to manage your boats wiring. No smoking wires from splices, or burnt bundles from a single short.
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Old 22-05-2015, 10:18   #13
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Re: 12V Negative - Shared or Per-Circuit?

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Or busbar or bussbar or at least according to wikipedia
Wikipedia can say anything. However, dictionaries only list one spelling - busbar. That's because the bus is short for "omnibus", or "for all", and buss can't be short for omnibus, can it?

Also I was wrong first time, it's busbar, not bus bar (or buss bar, or bussbar).

What adds to the confusion is that Buss is a manufacturer of busbars.

Busbar. Glad we got that sorted out. Where were we?

Yours somewhat pedandically,
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Old 22-05-2015, 10:19   #14
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Re: 12V Negative - Shared or Per-Circuit?

I like the bus bar concept, though I'm wary of giving up the protection of double insulation that duplex wiring offers.

Quote:
Originally Posted by S/V Alchemy View Post
And let's not neglect "individually fused/circuit breakered". It's the royal road to solving outages.
I made sure to do this when I replaced my electrical panel. The new panel has an individual switch for each load (16 available circuits, of which I'm using 14).

The panel is only for switching - fuses are located in an electrical cabinet I installed a few feet away. Power runs from battery to switch panel, distributed to individual circuit switches, then from switch to fuse to load.

Originally I had a negative bus bar in the fuse cabinet so all wiring to loads was duplex, but I'm thinking that a few strategically located negative buses will result in less wiring running around the boat.
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Old 22-05-2015, 10:20   #15
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Re: 12V Negative - Shared or Per-Circuit?

I'm on board with the single negative bus with bus bars or terminal strips located as needed. Eight gauge wire should be fine for your negative bus. You should also seriously consider using primary wire that is color coded for the positive feeds to various loads. It will make trouble shooting in the future much, much easier.

Here's a pic of a terminal strip from my recently rewired Stevens 47. gregsmarinewire.com is a great source for wire. Fast service, reasonable prices. Bestboatwire.com is also good and has a broader selection of other parts (bus bars, etc).

Good luck with your project.
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