February 13


Crimping Wire Terminals for Battery Cables

By Jan C. Athenstädt

February 13, 2019

One of the most important things to consider when (re-)wiring a boat is the connection of the batteries and other high-current consumers. Due to the high currents, the risk of a cable fire due to bad connections should not be neglected. In this tutorial, we show you how to crimp lugs for wires with larger diameter (from 10mm² / 7 AWG and larger).

Tools and Material


Properly crimped battery cables installed on a boat

A note on Crimping Tools

In order to get a proper crimp, it is crucial to use a proper tool. Crimping cables with a vice or by hammering them with a chisel is really bad practice and does not lead to a safe connection. Make sure to use the right tool for the job!

While it does pay off to invest in a high-quality tool if you need it regularly, there are quite reasonable priced alternatives such as this one that even comes with wire cutters. According to the reviews, the quality of these cheap alternatives seems to vary quite a bit, so make sure to do a couple test crimps and send it back if you are not satisfied!

Tensile Forces for Connectors

According to ISO 13297-2019, crimp-on terminals and connectors shall be attached with the type of crimping tool designed for the termination used. (See also our 10 Commandments for Electrical Systems on Yachts.)

Conductor-to-connector and conductor-to-terminal connections shall be capable of withstanding a tensile force equal to at least the value in the table below without separating.

Cross Section (mm²)

corresponding AWG

Tensile Force N





























0 (1/0)



000 (3/0)



0000 (4/0)





A tensile force of 10 Newton corresponds roughly to lifting the weight of around 1 kg (2.2 lbs). The table above shows, that a crimping connection on a 10 mm² (AWG 7) wire has to be able to withstand the pull of more than 22 kg (more than 48 lbs). 

And even small connectors are able to withstand surprisingly high forces when properly crimped. The crimp connection on a 1.5-mm² (AWG 15) was able to hold the weight of a full bucket of paint without any problems.

We will now show you how to properly crimp wire terminals.

A good 1.5-mm² (AWG 15) crimp connection should hold the weight of a 10-liters (2.5 gal) paint bucket.

How to Crimp Wires: 3-Step-Tutorial


Preparation of the Cable

Before you start crimping you have to strip off the insulation at the end of the cable. It is absolutely crucial to be careful in this step: If you accidentally cut through some of the strands, the required diameter will be reduced and the lug might not hold properly.

Make sure to select cable lugs that have the same size as your wire

Place the cable lug next to the wire to measure the length of insulation to be stripped.

Mark the length of the cable where the insulation is supposed to be stripped with a slight cut.

Now it's time to carefully cut around the insulation. Make sure to cut so lightly that none of the strands of the cable is damaged!

Make sure that you did not cut any strand by accident by checking the part of the insulation you just removed.

Now place the lug over the wire. It should be a tight fit, barely touching the insulation when the strands hit the bottom of the lug.

For lugs with open ends, make sure that the stripped strands are slightly longer than the lug.

Some closed lugs have a little spy-hole which helps you determine, whether the strands are all the way in before crimping the wire.


Crimping the Wire

Here comes the main step: In a proper crimp, the lug is pressed so tightly around the strands of the cable that they form a solid piece of copper. This ensures a good conductivity and strong hold: It is impossible to pull off a properly crimped cable with bare hands.

Make sure your crimping tool is set to the proper wire size. In this case, it's set to 25 mm². If you want to crimp AWG-Wire, make sure to use the conversion table that usually comes with the crimping tool.

Place the lug into the crimping tool and close it just far enough to hold the lug. For long lugs with enough space for two crimpings, start at the side facing away from the insulation (According to this article. There are smart people who argue that you should start at the other end. Technically, both ways should be fine.)

For smaller lugs, place the crimping tool in the center of the lug.

Now is the big moment. Push the wire firmly towards the lug and press down the crimping tool until it is closed all the way. (Especially for larger wire sizes it might be a good idea to have a second person: one to hold the wire in place and one for the operation of the crimping tool.)

Already after the first crimp, you should not be able to pull off the lug with bare hands for larger wire sizes. (See section on tensile strengths.) Give it a try as a check if the crimp holds properly.

The crimping tool should have evenly pressed the lug into a hexagonal pattern.

For the longer variation, crimp the wire a second time halfway between the first crimp and the end of the lug.

This is what a properly crimped lug for a battery cable should look like.


Shrink Wrap the Wire Terminal

Using heat shrink tubing on crimped cables is good practice, in particular in a marine environment. It helps to protect the wire from water intrusion and the resulting corrosion and provides a mechanical protection and insulation of the bare lug.

Place a sufficiently large heat shrink tube over the lug such that it ends just where the round part gets flat.

Now carefully and evenly apply heat to the heat shrink tube. Ideally you should use an electric heat gun with the proper nozzle attachment, but if you are careful(!), a butane soldering torch with the proper nozzle works as well.

If the heat shrink tube has contracted evenly and the glue has melted all around the cable, you are done. Congratulations, you just crimped a wire like a pro!

Did you find this tutorial helpful? Make sure to sign up below to hear about new tutorials and upcoming courses!

Jan C. Athenstädt

About the author

Jan runs KlabauterKiste, the German online magazine for boatowners and Klabauter-Shop, an online shop for boat supplies. He has worked as deckhand and bosun on various tall ships and has been responsible for rewiring and maintaining the electrical systems of various yachts and research vessels. Currently, he is fixing up an old Laurin32 in Hamburg, preparing the yacht for extensive bluewater cruising. Jan holds a PhD in Computer Science from Konstanz University and a masters from Karlsruhe Institute of Technology.

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