They tame stranded wire and make connections secure
![](https://stage.goodoldboat.com/wp-content/uploads/2019/03/Screen-Shot-2019-02-25-at-5.45.03-PM.png)
A ferrule slips easily over a stranded wire and ensures that the connection is as secure as it can be in devices that are connected with bare wire rather than crimped-on terminals
On a boat, stranded copper wires are the norm, and connections are usually made using crimped ring terminals. A lot of the electrical devices on board, however, incorporate screw-terminal blocks. On Nine of Cups, the Adler-Barbour refrigerator compressor and the 120-volt AC selector switch, as well as some of the electronics, use screw terminals. For most of the equipment intended for use on a boat, these screw terminals are designed so that it is acceptable to simply insert the stranded wire into the terminal and lock it into place with the screw. A better method is to use a ferrule.
A basic ferrule is a short tin-plated copper tube that is slipped onto the end of a stripped wire and crimped in place. The crimped ferrule holds the individual strands of wire together and forms a gas-tight seal. To make assembly easier and to increase wire durability, most ferrules also have a conical-shaped plastic collar on one end of the copper tube. Ferrules come in a host of different sizes designed to fit wires from AWG 28 to AWG 1. The plastic collars are color-coded to make it easy to identify the size of the ferrule.
Ferrules have two significant advantages over bare wire:
![](https://stage.goodoldboat.com/wp-content/uploads/2019/03/Image_004-1.png)
Adler-Barbour terminal block
No stray strands –I used 8 AWG wire to power my Adler- Barbour compressor, but the terminal block is located in a hard-to-see place and I found it difficult to push the stranded wire into the screw terminal without a stray strand or two of wire separating from the bundle. When pushing the entire wire bundle into the funnel shape of the ferrule collar, stray strands are easy to spot.
![](https://stage.goodoldboat.com/wp-content/uploads/2019/03/Image_005-1.png)
the selector switch.
Better long-term connection –Weidmuller, a company that manufactures electrical components, including ferrules, did a long-term study of wire connections using solid wire, stranded wire, and stranded wire terminated in ferrules. The study measured the electrical resistance of the connections in a standard environment as well as a salty environment over a period of years. The solid wire performed the best, showing little change in the electrical resistance of the connection over a four-year period, whereas the stranded wire showed a significant increase in the electrical resistance with time. In fact, the study showed the resistance of the stranded-wire connection reached an unsafe level in just over three years in a salty environment. The addition of ferrules to the stranded wire resulted in a connection that performed almost as well as the solid wire.
![](https://stage.goodoldboat.com/wp-content/uploads/2019/03/Image_001-1.png)
Ferrules are color-coded for size and can be purchased in a kit that includes a crimping tool.
A special tool is required to properly crimp a ferrule, but for those not expecting to crimp hundreds of connections, an inexpensive tool can be purchased online. For less than $30, I bought a kit that included a crimper and a large assortment of ferrules that will suffice for most of the electrical work on the boat.
Resources
- American Boat and Yacht Council Inc. ABYC E-11: AC and DC Electrical Systems on Boats
- Link to Weidmuller Ferrules White Paper: search with “white paper weidmuller”
- “Marine Electrical Wiring 101,” Good Old Boat, July 2014