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
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)
Tensile Force N
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.
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.
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.
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.
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