Tuesday, March 29, 2016

Crimping Lugs onto Large Gauge Electrical Wires

First of all, thank you, all of you, for your patience and for your well wishes.  They are very much appreciated!  The neck surgery was to correct a nerve pinch in my cervical spine that was causing me to lose the use of my right hand.  Recovery is proceeding apace.

OK, enough of that. 

Aboard s/v Pilgrim, Jeff & Anne continue their refit.  Today they show us how to make up terminals on heavy gauge wire...  I do encourage you to check out the comments on the original post - there are some useful pointers in there to suitable tools for crimping.
Our recent installation of Pilgrim’s primary 12V DC wiring required the numerous large gauge, 4 to 00, electrical wires.  If you’re wondering which is the larger wire a 4 or 00, then check out our previous post – Let’s Talk Marine Wire, October 18, 2015.

Large gauge wire runs at electrical panel and starter battery.

Large gauge wire runs at house battery bank.

Here are a few things I picked up about crimping lugs onto large gauge wires.

Happiness is having the right tools for the job at hand.  The key for installing wire terminals on large gauge wire is having the proper crimping tool.   Unfortunately appropriately sized, quality crimpers are expensive and rarely part of the DIY sailor’s quiver of tools.  Fortunately I am currently able to borrow a great crimping tool with dies for crimping 6ga through 4/0ga. 

If anyone out can recommend a source for purchasing a quality pair of crimpers functional on 6 to 2/0 wire, then please share the info in the comments.

Tools and materials:  Clockwise from the top - heat gun, medium duty wire cutters (blue handle), large gauge wire crimper with multiple dies, 2/0 x 5/16 post lugs, heat shrink tubing,  2/0 wire.

Heavy duty wire cutter and a sharpie style marker are essential tools missing from the image above. 

I’m not certain if there is a technical difference between lugs and ring terminals.  In my vernacular ring terminals are used with smaller gauge wire and typically have heat shrink insulation already installed.  Lugs are typically non-insulated fittings for larger wire.  If anyone out there has a different definition / delineation, then please let me know.

Ring terminals and lugs need to be sized to the correct gauge of wire and to the correct post diameter.  In the image below both lugs are for 2/0 wire.  The lug on the right fits a 3/8” post and the one on the left fits a ¼” post.

22ga to 8ga insulated ring terminals on left.  6ga to 2/0ga lugs on right.

Two 2/0ga lugs with holes for different size posts.

Avoid aluminum when purchasing wire connectors.  Like marine wire all terminals and lugs should be tinned copper.

I’ve found my medium duty wire cutters will realistically work on wire up to around 1 gauge.  0 through 4/0 wire will require large cable cutters.  Sailing vessels should be carrying large cable cutters to deal with wire rigging in the event of a dismasting (See our C’est la Vie post: Dis-masted – Part 2 if you doubt the necessity of having large cable cutters aboard.)  Cutting 4/0 wire is easy with the large cable cutters. 

Once the wire is cut to the proper length, slide a section of heat shrink tubing for each lug to be installed onto the wire.  Sliding the heat shrink over the wire at this point will aid in avoiding any fraying of the wire once the insulation is removed.  Next, using the lug as a guide mark the amount of insulation to be stripped off the end of the wire.

The medium duty wire cutters are my tool of choice for stripping wiring larger than 10 gauge.

Stripping 2/0 wire using medium sized wire cutter.

Apply gentle pressure to the handles while rotating the cutters around the wire.  I prefer to rotate back and forth through 180 degrees.  Rotating through 360 degrees is ergonomically awkward and often results in a spiral cut on the insulation.  Stop the motion when you begin to feel the strands of copper against the edge of the cutters. Knowing when to stop cutting and how much pressure to apply comes with practice. 

Once the insulation is gone, I move directly to installing the lug.  Expediency at this step will aid in avoiding any fraying of the small stands of copper wire. 

Crimping a lug on a 2/0 battery cable.

Once the crimping is completed, I give the lug a through visual quality inspection.  If satisfied with the connection, then slide the heat shrink tubing over the junction and let the heat gun do the rest.

Numerous 2/0ga battery wires in Pilgrim's house battery bank.

Happy Crimping!


  1. Re: crimper recommendation

    Maine Sail recommended the FTZ 94284, and I took his advice (usually a good practice in my experience). I got mine at kljack.com; it's also available at Sailboatowners.com (http://shop.sailboatowners.com/prod.php?2500).

    Its dies support up to 4/0 with power lugs and 250 MCM (1 size over 4/0) with flared starter lugs. I've mostly crimped 2-gauge cables, with power lugs from GenuineDealz (our 'windlass' will probably always be me, up on the bow with a pair of leather gloves, yanking up the anchor, so no need for larger cables soon). That said, the FTZ crimper seems very well made, and I'm sure it would crimp larger cables quite happily.

    At ~$175, it's not cheap, but I've been very happy with it, and expect to use it for many years. Recommended.

    1. I bought this crimper and it's paid for itself already.


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