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Northeaster 07-12-2009 08:10 PM

Typical wiring to / from battery selector switch??
Hi folks,

Just tracing out some wiring, as I don't think my DC feed from battery selector switch, to DC panel, is sized large enough. It looks to be about 14 ga, where most individual circuits are 14 - 16 ga.

I am trying to determine where all of the wires go , from the battery selector switch. This is a 30 ft, 30 year old sailboat.

Of course, I have 3 connections on the back of the switch: (swich is a make b4 break, off, 1, both, 2 type of switch.

1. battery 1 pos connection
- has battery cable and a small gauge wire that goes to DC panel voltmeter

2. battery 2 (2 batteries inb this bank) pos connection
- has battery cable and a small gauge wire that goes to DC panel voltmeter

3. common - have 1 red wire that goes to alternator
- have 1 red wire that goes to feed DC panel (believe to be too small guage)
- have another red wire, small gauge / style as feed to DC panel..........Where do you think it would go?????

Other than the common feeding the DC panel, and being connected to the alternator, for charging either bank, where would this other wire likely go??

Thanks in advance for the help!!!!

LookingForCruiser 07-12-2009 08:24 PM

14 gauge wire is probably woefully undersized for the main feed to the panel. I just redid mine with 4 gauge, as I don't actually have any equipment other than nav lights and a VHF radio. If you have "stuff" in your boat you'll want to do something larger than that.

Here's the web page I used when sizing the wires I have running throughout my boat:

ABYC Wiring Standards

therapy23 07-12-2009 08:26 PM

Maybe to the bilge pump?

btrayfors 07-12-2009 08:34 PM


Originally Posted by therapy23 (Post 504744)
Maybe to the bilge pump?

Hopefully, NOT! What would happen if the main battery switch were turned OFF?


Northeaster 07-12-2009 08:56 PM

Actually, the Bilge pump is wired from the DC panel, which gets shut off as well! Perhaps not smart, but it was like that when i bought the boat a couple of years ago.
My bilge was quite dirty / oily after years of neglect, and I did not want a permanently wired / auto bige pump, that would put out oily water.
I now have the bilge to a pretty clean state, so I could likely rethink this now.
However, I have a traditional stuffing box / hose in good repair, and close all 3 seacocks if I am going off the boat for more than an hour, etc, so, for me, I don't really see the need for a directly wired / auto bilge pump.

Back to the original question, where else could that other wire go, from the common battery switch post???

PS. Bill - my Iota 45 amp charger has been working well. Great recommendation, and great price as well.

scottyt 07-12-2009 11:53 PM

does it go to the charger?

patrickrea 07-13-2009 02:49 AM

The wire size from the disconnect switch to the panel will depend on how much power your are pulling when everything is on. Total up your amperage and the check that against the ABYC chart for the distance your are travelling. I would guess that if your panel is like mine, you likely will need 8ga or possibly 4ga.

Northeaster 07-13-2009 08:15 AM

ScottyT- no, it does not go to the charger. I put the new Iota charger in this spring. It goes connected to the AC panel, and then directly to one of the batteries in bank 2.

The wire may even have been an old bilge pump, for example, that is no longer there / in use. Who knows. Whereever it goes, it is getting DC voltage, that is not wired through the panel, and it looks like original wiring.

Patrick - thanks for the advice on the wiring chart. I will calculate things before replacing. I still may ot go with the "proper" size though, as I will not be having all of my DC lights, water, bilge, pumps, etc on at once, and even a jump from 14 Ga to 10 Ga would be a huge improvement. Getting a larger wire over there may be very difficult!

therapy23 07-13-2009 06:48 PM


Originally Posted by Northeaster (Post 504840)

I still may ot go with the "proper" size though, as I will not be having all of my DC lights, water, bilge, pumps, etc on at once,

Only in some emergency situation.

Northeaster 07-13-2009 09:38 PM

Therapy - you are right , of course.. it is better to make it perfect. However, it has worked for 30 years with the current wiring, and is still floating. If I improve things by changing the feed from 14 ga to 10 or 8 ga, for example, it will ceratinly be better than it has been (for 30 years).
re: emergency, yes some things like running lights, steaming light, bilge pump and electronics could all be used at once. But I doubt that I would also "need" to turn on the water pressure pump, anchor light (assuming we are moving), all five or six cabin lights, etc, during an emergency as well. So I think that some common sense can be used in determining wire size.

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