Battery Cable size??

Jan 22, 2008
101
Hunter 40.5 New Bern NC
Increasing the house bank, adding 2 additional group 31 AGM to bring the total to 4 house with a combined 420 amp hours my question; cable size wiring in parallel, with the longest run's of 12" to 18" max, can i use the ready made 4.0 cables or should i go with the heavier 2.0 cables ??
Thanks much,
Capt. Ron
S/V Wind Dreamer
40.5 Legend
 
Jan 4, 2010
1,037
Farr 30 San Francisco
Lets pray for Maine Sail to weigh in. What current will be flowing in the cables? How many amps does your alternator put out? If that hasn't been upgraded then maybe do nothing? The size of those cables also dictates the fusing at the battery, which you should do. Per West Marine 2/0 can handle 330A at which point it will be really hot it should be noted. This http://bdbatteries.com/wirerules.php calculator suggests that at 120A you only lose 0.06V on a 3 ft round trip.
 
Sep 28, 2008
922
Canadian Sailcraft CS27 Victoria B.C.
I wire all battery interconnects the same size as the wiring to starter, switch, and negative bus. The smallest I use is 1/0, most often 2/0. I have used 4/0 a few times on large banks with longer runs.

What size is the cabling to starter, switch, etc?
 

CYQK

.
Sep 11, 2009
576
beneteau first 42 kenora
Thing is your not hurting a thing by going larger
All wiring on my boat was done kick-ass size on the load circuits
Bought those kick-ass size lugs recomended by mainsail
Loads and heat spell fire if corrosion or decay occurs
Protect the admiral at all costs
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Increasing the house bank, adding 2 additional group 31 AGM to bring the total to 4 house with a combined 420 amp hours my question; cable size wiring in parallel, with the longest run's of 12" to 18" max, can i use the ready made 4.0 cables or should i go with the heavier 2.0 cables ??
Thanks much,
Capt. Ron
S/V Wind Dreamer
40.5 Legend
What size is the rest of your high amperage wire? How is the boat wired? At a bare minimum it should match what is already there but what is there may already undersized.. Unfortunately Hunter and many other US builders undersized this wire for years with some boats using high amperage starter wiring as small as 4GA. Today those same builders are using 1/0 and 2/0 wire and often times with shorter circuit lengths.....

I don't know what 2.0 wire or 4.0 wire is but 4/0 (0000) wire is much larger than 2/0 (00) wire. 2GA (not 2/0) is larger than 4GA (not 4/0) but 4GA is really pretty undersized for a 40 footer, especially if the vessel has a windlass.

Here are some minimum manufacturer suggestions for battery/starter cable from Westerbeke & Universal.

Universal / Westerbeke BATTERY CABLE REQUIREMENTS (wire length round trip)

2GA = 8'
1GA = 10'
1/0 = 14'
2/0 = 18'
3/0 = 22'
4/0 = 28'


They no longer even suggest 4GA.. It does not take much to have 14' of wire circuit length even with batteries just a few feet from the engine. Remember, these numbers are wire lengths along the conductor not an as the crow flies distance.

The last Hunter 40 I was on, was from the early 90's, and used 4GA wire in a circuit approaching 25'. Owner was on his third starter motor in 6 years and peak low voltage at the stater was sagging to 4.2V during cranking. I would suggest using the Westerbeke guidance as a bare minimum and this means the entire round trip circuit length...
 
Jan 22, 2008
101
Hunter 40.5 New Bern NC
Maine,

First of all I meant to say (as you corrected) that the current cable size is 2 ga., and I was considering using 4 ga. to add the additional 2 batteries to the existing house bank, I also added 2/120 watt solar panels thru a BlueSea controller, after reading your comments and suggestions below I will up the battery cable to 2ga, to connect the two additional batteries to the house bank, I do have a windlass and the wire size to the windlass is also 2ga. the engine is a Volvo 50 hp with the standard alternator, and a dedicated group 27 AGM start battery that also supplies the power to the windlass.
Added the solar to help keep the batteries up when anchored out, all lighting is now LED, the biggest draw I have is the Adler Barbour Ref and freezer units, I'm not on a mooring, in a marina slip hooked up to shore power, also have a Heart 3000 watt inverter/charger and a Honda 2000 portable generator that is only used occasionally when we are anchored out for 2/4 days.
What else am i missing,
Thanks much
Ron

What size is the rest of your high amperage wire? How is the boat wired? At a bare minimum it should match what is already there but what is there may already undersized.. Unfortunately Hunter and many other US builders undersized this wire for years with some boats using high amperage starter wiring as small as 4GA. Today those same builders are using 1/0 and 2/0 wire and often times with shorter circuit lengths.....

I don't know what 2.0 wire or 4.0 wire is but 4/0 (0000) wire is much larger than 2/0 (00) wire. 2GA (not 2/0) is larger than 4GA (not 4/0) but 4GA is really pretty undersized for a 40 footer, especially if the vessel has a windlass.

Here are some minimum manufacturer suggestions for battery/starter cable from Westerbeke & Universal.

Universal / Westerbeke BATTERY CABLE REQUIREMENTS (wire length round trip)

2GA = 8'
1GA = 10'
1/0 = 14'
2/0 = 18'
3/0 = 22'
4/0 = 28'


They no longer even suggest 4GA.. It does not take much to have 14' of wire circuit length even with batteries just a few feet from the engine. Remember, these numbers are wire lengths along the conductor not an as the crow flies distance.

The last Hunter 40 I was on, was from the early 90's, and used 4GA wire in a circuit approaching 25'. Owner was on his third starter motor in 6 years and peak low voltage at the stater was sagging to 4.2V during cranking. I would suggest using the Westerbeke guidance as a bare minimum and this means the entire round trip circuit length...