Battery Cables

Benny · Aug 30, 2006

Not necessarily too small.

The gauge of the cable is directly related to the current that must go through it (the load). If the load draws more current than the cable can carry the cable will heat up. Turn on all the lights, radio, water pump, 12V fans etc. See if the cables heat up. If they do then you need to upgrade as you would have a potential fire hazard in your hands. If they remain cool their capacity to carry your load is adequate.They estimate the safe allowable current in amps for the cabin of a boat is 80 AMPs and for this current with a conductor wire round trip of 10 ft the recommended wire would be #6 gauge. If you were to double the conductor wire to a 20 ft round trip the #2 gauge would be recommended. 80 amps is a lot of juice and I doubt very much your maximum combined load would even aproach half of that. You can run 40 amps trough a conductor wire round trip of 30 FT with #6 gauge wire. Engine starter loads are larger so a #2 gauge wire would be recommended for the starter circuit; if your house bank is connected can be called to act as a starting bank then you should upgrade to #2. But if your house bank is a stand alone dedicated use then it would seem that what you have is adequate. There is a formula for sizing wire:CM = (I*L*10.75) / (E)CM= Wire size in circular millsI = Current in Amps (load)L = Length of wire Round TripE = Allowable voltage drop- generally 0.36Size Conversion Table CM Wire Gauge 1,620 18 2,580 16 4,110 14 6,530 1210,380 1016,510 826,240 641,740 466,350 283,690 1105,600 0133,100 00Figure out the consumption load in amps of all your componentes that may be running at once and plug it in the formula. Measure the round trip distance to your battery switch and round up to an additional 5 feet and plug it in the formula. Get your CM and find the corresponding gauge size. I have seen dedicated house batteries in a daysailer safely using a #10 gauge. It all depends on the loads and the way it is wired.

Bill Roosa · Aug 30, 2006

Benny is right

but don't go turning everything on to see if the cables get hot. You could start a fire.The load to design for is the max current you would ever put through the wire. This does not have to be "everything turned on at once". You are not going to have the anchor light and the running lights on at the same time. The same goes for other loads. Without knowing what equipment you have on board it is hard to advise you. The max load is usually the biggest single load plus all the other things that are on when the biggest load is turned on. Inverters running hair dryers and starter motors come to mind. You do not have to power the starter motor and the inverter both. This could mean that you have adequate wiring (or not).What equipment besides the normal running, anchor, cabin lights stuff do you have?

Don · Aug 30, 2006

consider voltage drop too

In addition to what Benny and Bill said, you may have sufficient size cables as is depending on your max load but there is a point at which the voltage drop becomes too great. If you follow Benny's formula, you will be right but check the total voltage drop to make sure as if it becomes too great, you could effectively increase the current load on a marginal cable.Don

jviss · Aug 30, 2006

That depends!

First, I would recommend that you verify anything you read here from some authoritative source, including the potentially wrong and life threatening advice I may give you! West Marine has excellent technical resources on this topic. Their information is based on the ABYC standards.Two things of immediate interest are Marine Wire chart and the Electrical Budget Worksheet that are found on this here:http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorListView?storeId=10001&langId=-1&catalogId=10001For your application your biggest current load may be the alternator to battery charging wire, connected to the B+ terminal on the alternator. Assuming a heavy duty alternator and external "intelligent" regulation, this could exceed 100 Amps. On my boat I have a 125 Amp alternator and I can see 100 Amps plus when I begin charging a bank that's down pretty far. Also, if you have a windlass, this can be a load in the 100 A neighborhood.Your shore power charger is probably not a big concern, as these are typically in the 10 A range. You still should make sure the wire is properly sized, and protected. A wiring system that is properly protected with fuses or circuit breakers should never cause a fire.I don't know where the supposed 80 Amp limit comes from, Benny, can you provide a reference? My friend's electric bow thruster on his 53' sailboat draws 750 Amps in use!Additionally, there is no "typical" allowable drop, it depends on the class of load. ABYC puts them in two classes, 3% and 10%. See the West Marine chart. Crimping is accomplished with - a crimper! There are several types, and for this wire size all are expensive. The least expensive is the one marketed by Ancor and sold in West Marine that you smash with a hammer to cripm: about $65.00. The one that looks like a bolt cutter is probably around $300. Maybe the boat yard can do it for you. At my yard they won't lend the tool, but if you bring the guy the wire he'll do it for free. If he has to go to your boat, it's $70/hr.I don't know what a "button connector" is.

Sunshine · Aug 30, 2006

Pay attention to the sailors

and not to the boys in the science club.

Ross · Aug 30, 2006

Sunshine, You are starting to get my attention.

Men of science understand terms like: power density, Ohms per unit length, voltage drop, amperes. Sailors may also under stand these terms and some may be able to apply them in a useful manner. If you disparage knowledge in favor of intuitive thinking you run the risk of leading others into danger.

Tom Spohn · Aug 30, 2006

Be safe

When I wired a previous boat I read articles on wiring, sizes, etc. Then I wired all 12 volt with 1/0 wire and had West Marine crimp on the appropriate fittings. May have been too bid, but I know it was not too small.

jviss · Aug 31, 2006

DC Clamp-on Ammeter

Best Christmas present I ever got is a multimeter with a current clamp that reads AC and DC Amps. I measured the current for everything and wrote it in my log book.What kind of alternator and regualtor do you have?

Fred Ficarra · Aug 31, 2006

Shippy,

These guys are GOOD! One more thing; always error on the side of caution. With wiring that means 'bigger'.

Scott · Aug 31, 2006

Funny coincidence!

I just came back from West Marine just now and I bought a red and black cable. It is an item that is a bit more pricey than I expected! A 48" Red 2-AWG was $46. The 16" Black 2-AWG was $37. They were packaged in 16", 32" and 48" lengths. If you have a greater length, I suppose you would have it made. I measured the old cable to to get the right length. I'm only replacing the cables from the starter to the switch on the positive side and from the neg battery post to the engine block on the negative side. The other cables don't look so bad so I didn't replace them after choking on the price (I am going to do some further scrutinization).I scratched my head in the store for a while when I was trying to think if I was replacing existing #4 or #2. Visually, I couldn't see much distinction so I figured I would take the larger wire to be safe even tho it was several extra $$$!BTW, I have a 27' boat with a 1GM engine, probably with the original alternator & starter (which I don't know what size or capacity they are).

Ross · Aug 31, 2006

I do hope you got kissed when you bought

that battery cable. Jamestown distributors sells ten foot rools of 2 gauge red or black for 21.19 USDEdited; to correct name of supplier.

Brad Hoff · Aug 31, 2006

Welding Wire

I used 100A welding wire for less that $1/ft. I know this is not approved wire for this type of use but it has been in for 5 years with no problems and it is also oversized. It is not tinned but I sealed each fitting with glued heat shrink to keep out moisture. There is also some concern about the possible lighter insulation cover on the wire. I have it all anchored in place and have seen no evidence of chafe. I figure if it can withstand shop floor use, it should work on my boat. One other advantage I found was the flexability of this cable as compared to the marine grade. I am not recommending this type of wire to be used, but I am planning to add two more golf cart batteries and will use it again.

Scott · Sep 1, 2006

Ross, I get some gift certificates ...

when I spend more money there

. As a typical boat owner, I get pulled by gravity towards stores that sell boaty things :{Hey Fred! Why are you avoiding the "dark" side. You're missed in there. I know, I was pretty mellowed out after vacation for a while, too. But your absence is really getting noticeable

I hope your cruise was great!

Ross · Sep 1, 2006

Skippy, try this link

http://www.jamestowndistributors.com/userportal/main.do;jsessionid=6A0841753D77AF89E2CA86D4AFF163B6Or this onehttp://www.hamiltonmarine.com/

RAD · Sep 1, 2006

Jamestown distributors

Last time I looked (about 5 min. ago) # 2 was 32.84 so thats 3.28 a footcopper price's change faster than I change my socks!!I just replaced some cables with 2/0 and what I did was go to my mom & pop auto supply store and they made up the cables with crimped eyes on each end and then when they looked up the price he says this is way to much and adjusted the price down,I think with all this rain this weekend I might replace some more and hope he does the right thing again.I paid 9.00 a foot with the labor to crimp included and WM wanted 12.50 a foot just for the cable

Stu Jackson · Sep 1, 2006

What can anyone do with 2/0 cables

on a boat unless it's for a (say, a Freedom) combined inverter charger connections to the battery banks?There is a BIG difference between 2/0 and #2.#2 makes sense, but 2/0?Are we just mistaking the gage of the wiring here, or is somebody going WAY overboard? NPI

Benny · Sep 1, 2006

RAD are you running a windlass?

2/0 is some serious power transmission cable. Most people will place a dedicated battery up near the bow to significantly reduce the wiring round trip distance and hook up a solenoid or relay to energize the circuit via a bow or cockpit switch.

Battery Cables

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Benny

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Scott

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Scott

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Benny