Barbed Wire - Installation of Barbed Wire

Installation of Barbed Wire

The most important and most time-consuming part of a barbed wire fence is constructing the corner post and the bracing assembly. A barbed wire fence is under tremendous tension, often up to half a ton, and so the corner post's sole function is to resist the tension of the fence spans connected to it. The bracing keeps the corner post vertical and prevents slack from developing in the fence.

Brace posts are placed in-line about 8 feet (2.4 m) from the corner post. A horizontal compression brace connects the top of the two posts, and a diagonal wire connects the top of the brace post to the bottom of the corner post. This diagonal wire prevents the brace post from leaning, which in turn allows the horizontal brace to prevent the corner post from leaning into the brace post. A second set of brace posts (forming a double brace) is used whenever the barbed wire span exceeds 200 feet (61 m).

When the barbed wire span exceeds 650 ft (200 m), a braced line assembly is added in-line. This has the function of a corner post and brace assembly but handles tension from opposite sides. It uses diagonal brace wire that connects the tops to the bottoms of all adjacent posts.

Line posts are installed along the span of the fence at intervals of 8 to 50 ft (2.4 to 15 m). An interval of 16 ft (4.9 m) is most common. Heavy livestock and crowded pasture demands the smaller spacing. The sole function of a line post is not to take up slack but to keep the barbed wire strands spaced equally and off the ground.

Once these posts and bracing have been erected, the wire is wrapped around one corner post, held with a hitch (a timber hitch works well for this) often using a staple to hold the height and then reeled out along the span of the fence replacing the role every 400 m. It is then wrapped around the opposite corner post, pulled tightly with wire stretchers, and sometimes nailed with more fence staples, although this may make readjustment of tension or replacement of the wire more difficult. Then it is attached to all of the line posts with fencing staples driven in partially to allow stretching of the wire.

There are several ways to anchor the wire to a corner post:

• Hand-knotting. The wire is wrapped around the corner post and knotted by hand. This is the most common method of attaching wire to a corner post. A timber hitch works well as it stays better with wire than with rope.
• Crimp sleeves. The wire is wrapped around the corner post and bound to the incoming wire using metal sleeves which are crimped using lock cutters. This method should be avoided because while sleeves can work well on repairs in the middle of the fence where there is not enough wire for hand knotting, they tend to slip when under tension.
• Wire vise. The wire is passed through a hole drilled into the corner post and is anchored on the far side.
• Wire wrap. The wire is wrapped around the corner post and wrapped onto a special, gritted helical wire which also wraps around the incoming wire, with friction holding it in place.

Barbed wire for agriculture use is typically double-strand 12½-gauge, zinc-coated (galvanized) steel and comes in rolls of 1,320 ft (400 m) length. Barbed wire is usually placed on the inner (pasture) side of the posts. Where a fence runs between two pastures livestock could be with the wire on the outside or on both sides of the fence.

Galvanized wire is classified into three categories; Classes I, II, and III. Class I has the thinnest coating and the shortest life expectancy. A wire with Class I coating will start showing general rusting in 8 to 10 years, while the same wire with Class III coating will show rust in 15 to 20 years. Aluminum-coated wire is occasionally used, and yields a longer life.

Corner posts are 6 to 8 inches (15 to 20 cm) in diameter or larger, and a minimum 8 feet (2.4 m) in length may consist of treated wood or from durable on-site trees such as osage orange, black locust, red cedar, or red mulberry, also railroad ties, telephone, and power poles are salvaged to be used as corner posts (poles and railroad ties were often treated with chemicals determined to be an environmental hazard and cannot be reused in some jurisdictions). In Canada spruce posts are sold for this purpose. Posts are 4 inches (10 cm) in diameter driven at least 4 feet (1.2 m) and may be anchored in a concrete base 20 inches (51 cm) square and 42 inches (110 cm) deep. Iron posts, if used, are a minimum 2.5 inches (64 mm) in diameter. Bracing wire is typically smooth 9-gauge. Line posts are set to a depth of about 30 inches (76 cm). Conversely, steel posts are not as stiff as wood, and wires are fastened with slips along fixed teeth, which means variations in driving height affect wire spacing.

During the First World War, screw pickets were used for the installation of wire obstacles; these were metal rods with eyelets for holding strands of wire, and a corkscrew-like end that could literally be screwed into the ground rather than hammered, so that wiring parties could work at night near enemy soldiers and not reveal their position by the sound of hammers.