Battery Cable Butt Connectors

Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
Quick Background
We bought our 42' Navigator (powerboat) about 5.5 years ago. One of the first upgrades was a complete re-do of the DC system. The team here helped A LOT and I thank you. However, I did shortcut it some and I now need to fix it.

Currently, the battery destination switches and charger are in the engine room. I know they need to be accessible in case of emergency and I need to move them up to the living space. Additionally, the battery charger (a Sterling 60A) is in a nearly inaccessible space. At the time I was unaware that the optional "remote control" really doesn't allow much "control" over anything. Meaning, I can't change the charging program that I need to change when I run the generator. More importantly, 60 amps is undersized for the task of charging an 880Ah bank.

Most of the wiring is 2/0 and 3/0. There are about seven or so of them that I need to lengthen by about two feet, perhaps three for a few, to allow them to reach the cabinet where the switches and, possibly, new charger will reside. I really want to avoid having to run all new cables as they are well secured, covered in corrugated sheathing, and very expensive to replace. Is there any MAJOR downside to using butt connectors for wire this size? I have a proper FTZ crimper and will fully insulate, shrink, and secure them from vibration.

We are discussing this over at Trawler Forum, but conscious is mixed. Opponents advocate ring terminals and studs, but doesn't that provide even more points of possible failure? If done correctly, wouldn't butts be just as secure? That said... I *may* opt to use studs to provide a service disconnect for the individual battery boxes where the eight house batteries live. Others say there is too much line loss, however, other than engine starting, no extreme loads will be present. I do want to add an inverter (if/when I replace the charger), but even then, that will only see light duty as we have a large genset should the need arise.

Thanks in advance.
 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Anything you add in between will constitue a porential point of failure. So either run all new wire or install either binding posts or a two-post bus bar, or even fuses as added safety. I don't think over-thinking this is healthy. You may end up doing nothing for the sake to trying to figure out what to do.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
I'm with @Brian D on this. I generally don't like butt splices on anything. I know 2/0 is expensive, I bought 25' of it this summer because one cable is 3" too short. How many feet of cable are we talking about? Is it possible to rethink the plan to shorten the runs? Can some of the old cable be repurposed?

When I was shopping for cable, I found Defender to have the lowest price if you are a Defender1st member. The cost difference easily paid for the membership.
 
Nov 14, 2013
200
Catalina 50 Seattle
I guess I'll be the black sheep and tell you I don't think this is a problem. If you use heavy-gauge barrel connectors and crimp them properly, you won't have any problem with current carrying capacity. As for additional points of failure, I'd sooner trust a crimped barrel than a post with split washer and nut. However, a barrel will significantly increase the bend radius of the cable at that point so if you need to bend the cables sharply in that neighborhood, that would argue for ring terminals, as would the need/desire for a bus bar, fuse, shunt, or other in-line accessory.
 

TomY

Alden Forum Moderator
Jun 22, 2004
2,758
Alden 38' Challenger yawl Rockport Harbor
Me too. I had to extend the heavy cables that run from the cockpit area to the bow windlass on my boat a few years ago. I borrowed a large crimper and simply crimped on the additional couple of feet i needed. I didn't really consider not doing this because the expense and time to replace the cables. So far, so good after several seasons. I'll take a look at them though, in the spring to make sure they are secure.
 
Jun 7, 2016
315
Catalina C30 Warwick, RI
Instead of using studs for a service disconnect switch, why not put these in its place? It will work as designed and might even look like it was intentionally designed that way.


204371.jpg
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Instead of using studs for a service disconnect switch, why not put these in its place? It will work as designed and might even look like it was intentionally designed that way.


View attachment 174367
:plus: The one issue I have had with the Blue Sea Switches is the mounting. It is necessary to remove the entire switch to access the mounting studs. Marinco (Blue Seas parent company) has a Pro series of switches which can be surface mounted and the switch part comes off leaving the base and studs attached to the bulkhead.


 
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
If you decided to use splice joint make sure you use double wall heat shrink tubing to protect the joint. Keep moisture and potential corrosion out.
 
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Likes: Rich Stidger
Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
Thanks for the replies y'all!

I may do a quick test with some spare wire and see if there is any difference in the overall resistance with and without a butt connector. Maybe I have a stud and ring connectors lying around that I can try that too. Still, at these gauges, is the voltage drop of a few ohms the real villain here? Isn't the failure point the one to worry more about? That said, would not a PROPER connection as laid out by Mainesail over at Marine How-To prevent said failure?

The radius bend is certainly food for thought. Thanks. Moreover, I COULD think thru re purposing a few of the runs to minimize the overall number of butt connection that would need to be made. As always, I'll have to sit in the engine bay and stare at it some, but that is typical of these types of projects.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
I'll have to sit in the engine bay and stare at it some, but that is typical of these types of projects.
Take a lot of photos and stare at them from the comfort of your easy chair. ;):beer:

If I had to prioritize the choices I'd list them as:

  1. Straight cable run, no connectors.
  2. Cable run broken by a needed switch.
  3. A butt connector that is well supported in a straight run (no curve or bend) and properly made and sealed.
  4. A stud necessary for a branch connection, i.e., one feed to two circuits.
  5. A stud whose sole purpose is to extend the cable run.
#3 and #4 are about equal.

Let us know what you decide.
 
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Likes: jssailem
Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Failure is going to happen when it decides to happen. You only can mitigate that failure by using the proper equipment.

The voltage is going to drop depending on the resistance of the cable. But, the current draw is what is going to do the most damage. The load is going to ask for x-amount of amps regardless of the size of the wire. The wiring, if insufficiently sized, will start to heat up and could cause the insulation to melt. Now we are asking for a fire to start. That's the problem we are facing.

Poor connectors can also cause this issue if the connection is inadequate. That will increase the resistance thus causing both voltage drop and heat buildup.

So don't be afraid to extend your cables as long as you do it correctly with the right parts. The best way is to just use a single length of cable. Granted, expensive, but the best solution.
 
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Likes: jssailem
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
This would be a good time to make a wiring diagram with the length and size of the wires used. And the fuses.