Battery Cables

[Jackman]

What size are you guys using? I have diesel now and want to replace my battery cables...they're large enough but they are shot from years in the bilge. More a of a safety thing for me.

Another thing...I'm thinking I need at least 100A capacity. That would be 2/0, 2 guage or 2AWG? I know one of them is thinner but I get confused about the nomenclature because I'm not an electrician.

Thanks,

Jack

 

[Pascal]

2 gauge or 2 awg is the same... 2/0 thought is much bigger...

the numbers go down to 0 but then go up with /0

ex 10 8 6 4 2 0 1/0 2/0 4/0

4/0 is as big as it gets, well reasonably, that's what i used for my inverter. on my 53 the main battery starter cables look like 2/0, they dont seem as big as the 4/0

why are you replacing them ? if the insulation is good, they should be fine ? my original cables look good..

 

[Avenger]

The size of the wire you use on DC circuits depends on the total length of the wire run (both directions) and load. The 100 Amp estimate may be a little low. I would measure the current wire length and verify the amperage with your engine supplier. There are tables to determine required wire sizes. If you can't find one (Worst Marine catalog usually has one) post your info here and we can look it up for you.

 

[Mike36c]

I ran 2/0 from my 8d's to my 330b's via a switch when I repowered. Remember, starters love heavy wire as voltage drop is minimum.

 

[the kuz]

Mine are also 2/0 installed durring repower to 330Bs on our 36C.

Regards, Bob K

 

[Brian Degulis]

You can't get into the ampacity tables here because your starters are a momentary load so they are undersized. In other words a 12v system on an 871 might draw 1000 amps on a cold day if you go to the tables that's going to be a giagantic cable because the size you read off the tables will be continous load. The actual cable used will be much smaller because the starter only runs for brief periods.

You need to tell us the egines you have and the system voltage.

Brian

 

[Jackman]

330B's 12V system with two *Ds with a 3 battery bank charger. I need to replace them because some of them seem compromised from being in the bilge and occasionally being subject to water over the last 25yrs. They have been in poor shape since I had the boat. I want to improve the system.

 

[SeaEric]

At the same time that you do this cable job, you may want to consider relocating your battery switches up out of the engine space if they're not already. On my boat the mains are down between the engines and in an emergency it would be nice to have them up and out where they can be easily accessed. This job is on my "to do" list, along with a few hundred other items.

 

[Brian Degulis]

330B's 12V system with two *Ds with a 3 battery bank charger. I need to replace them because some of them seem compromised from being in the bilge and occasionally being subject to water over the last 25yrs. They have been in poor shape since I had the boat. I want to improve the system.

1/0 will work 2/0 if the runs are long like over 10' Remember the heavier you go the better.

I don't know where your located but if your near the Tampa Fl area PM me We have all the tools to make um up and I can probably save you some money on the cable and ends.

Brian

 

[Pascal]

good point about the switches... it's on my list too !

I have the older styled blad switches that you pull down, I'm thinking about just adding an emergency pull cable that would let me pull the levers without opening the ER doors.

 

[Jackman]

I talked with an engineer who did some calculations and determined that 2 guage (2 lines per connection) gives about 80 more amps of capacity. 2guage versus 2/0 is easier to handle and cheaper....what are the pros and cons of doing something like this? I'm not an electrician..hence the questions.

Forgot to mention I also have 50ft rolls of red and black 2guage...not 2/0, that I have no use for until maybe now.

Opinions?

Thanks,

Jack

 

[Boatsb]

OK I will chime in on the basic physics. 2 x 2ga is not the same as a wire with the same amount of wire in it. Electricity seeks the path of least resistance and will heat up the 2 Gage way to much. If one were to have a bad connection you could fry the other.

Now with the basics from what is approved and used.

A single cable of suitable size is the only way to do it. That is the ABYC and USCG standard. No movement here and if something were to go wrong the insurance company would have an easy out.

Dont scrimp on certain items.
1) Fire extinguishers
2) PFD'd
3) Electrical cable
4) fuel

Kind of like don't screw with your proctologist.

 

[krush]

I'd say do it! It's cheaper and as long as you get the connections at the end fine, the electricity doesn't know any difference between going across 2 or 3 wires.

Only downside is you have more connections which just means more places for corrosion and resistance.

 

[Jackman]

Okay...but you are using two wires per sonnection so the load is split in half...so heat should be split equally as well. Its not like pulling a full load off of one wire of 2guage.

Just got me thinking. Its healthy to think...but not actually do!

 

[Boatsb]

Theory is not practice and 2 wires splitting a load from a common source to a common destination is a bad practice. Electricity will not meter itself accordingly. look at the NEC (national electrical codes) and ABYC before trying something against their requirements.

 

[Brian Degulis]

It all comes down to circular mils which is the amount of copper in the wire 2 Ga is 66361 2/0 is 133056 so 2 lenghs of 2 ga is 132722 just slightly less than the 2/0.

If I already had it I would use it but I would use whatever size lug I needed to put both 2 ga wires in one lug crimp or krimp and solder and seal it up with heat shrink tubing. Then I would use short pieces of heat shrink to wrap the cables together keep everything color coded and make a nice neat installation.

It's true that if one cable where to be cut te other would burn but the same is true if the larger cable were to but partially cut. I'M not seeing any saftey hazard here nor do I believe it would be a problem with insurance or survey. I have 2 lenghs of 2/0 running to my inverter and it was no problem on survey.

Brian

 

[krush]

Look at the NEC (national electrical codes) and ABYC before trying something against their requirements.

Codes are just boilerplate requirements, they are not physics. There is a reason engineers are allowed to design stuff that isn't explicitly stated in the code.

Using your train of thought, what keeps the current in a single wire from traveling all on one side of the wire? Two wires also have more surface area to dissipate heat better (also heard somewhere that current travels along the outer circumference of wire...could be a myth though). I know you stated what the code says, but you can satisfy the spirit of the code in a million different ways.

 

[Boatsb]

Not according to the insurance company. they look for the way out.

Coming from the electronics side we are quite aware of current and amperage and how to get it from point A to B. 1 path always. If there is a second path it is redundant not cumulative.

FYI if you were to use 2 smaller wires and one failed the second could catch fire. I believe the standard would be each wire would need to be of suitable size to carry the current.

 

[Brian Degulis]

If we were talking about an ordinary circuit with over current protection and rated for continous duty I would agree with you. This is a starter circuit the correct cable size would never handle the amperage if it were continous. With the correct cable size if you were to turn off the fuel and hold the starter button down the cable or the starter would burn up if the battery bank was large enough to keep it running. As far as cutting one cable and the other burning sure that could happen but the same thing would happen if you partialy cut the correct size cable.

If you put both cables into a common lug there realy isn't any diffrence between that and one cable it just comes down to the amount of copper.

Brian

 

[Pascal]

2/0 is $15 a foot at Worst Marine prices... probably $10/11 a foot elsewhere...

you're going to spend a few hours on this and try to save... 20', 30' of cable ?? $300 ?

leave the old cables alone then... chances are they're still fine.