Pole Line Building

Part of Telephony

Step-by-step construction of a wooden pole telephone line — from route selection through final wire stringing.

Why This Matters

Pole line construction is the most labor-intensive part of building a rural telephone network, and it rewards careful planning and technique far more than brute force. A line built well lasts 30-50 years with modest maintenance. A line built carelessly may need remedial work within 5 years and fail structurally within 10.

The skills required — route surveying, pole setting, hardware installation, wire stringing — are not highly specialized but they do require attention to detail and physical stamina. A team of four people can build roughly 1-2 km of pole line per day in reasonable terrain with prepared materials. Understanding each step lets you plan work realistically, organize teams efficiently, and identify where quality matters most.

Route Selection

Before touching a shovel, walk the proposed route carefully. Look for:

Grade changes: Avoid steep slopes where possible. Wire tensioned along a slope exerts a lateral force on every pole in the run; this force increases on steep grades. If you must cross steep terrain, add anchor poles and guys at the top and bottom of each significant grade change.

Vegetation: Clear a path 3-4 meters wide centered on the proposed line route. This clear zone allows maintenance vehicle access, prevents tree limbs from falling on wires, and reduces shading of wooden poles (shading traps moisture and accelerates rot). Document what clearing work is needed before pole setting begins.

Crossings: Identify every point where you must cross a road, stream, or power line. Road crossings require additional pole height to achieve required clearance (minimum 5.2 meters over roads for vehicles). Stream crossings require long spans with heavier wire or cables. Power line crossings require height coordination to maintain safe separation.

Soil conditions: Examine soil type along the route. Sand and gravel soils require deeper pole settings than clay. Rocky ground may require blasting or drilling to set poles. Log all observations so you can adjust pole specifications before purchase.

Pole Selection and Treatment

Select poles from straight-grained hardwood or treated softwood. Acceptable species include black locust, red cedar, white oak, Douglas fir (treated), and southern yellow pine (treated). Locust and cedar have natural rot resistance; other species require pressure treatment with preservative.

For telephone plant, poles should have a minimum 6-meter length with 1.2-1.4 meters of burial depth. The top circumference should be at least 90 cm (about 29 cm diameter). Poles that are too slender deflect excessively under wire tension loads.

If pressure treatment is unavailable, field-treat buried sections: heat coal tar, petroleum tar, or copper naphthenate dissolved in oil to fluid consistency. Coat the bottom 1.5 meters of the pole thoroughly and allow to penetrate before setting. This extends service life by 5-15 years depending on soil conditions.

Setting Poles

Dig the hole 300-400 mm in diameter at the top, tapering if possible to a tighter fit at the bottom. Depth should be one-sixth of pole length plus 0.3 meters minimum — a 6-meter pole requires 1.0-1.3 meters of burial. Increase depth by 300 mm in sandy soil.

Before setting, use a transit or water level to establish the correct alignment. All poles in a straight run should be collinear. Deviation greater than 300 mm per 100 meters of line looks unprofessional and can indicate angular errors that will affect wire tensioning.

Lower the pole into the hole using a gin pole (a short pole with a pulley at the top) and a block-and-tackle or sheerlegs tripod. Never let the pole fall freely into the hole — the bottom will be damaged and the alignment will be nearly impossible to control. Have one person at the base guiding the butt into the hole while others control the rope.

Once upright, plumb the pole in both axes using a level or plumb bob. Backfill in 200 mm layers, tamping each layer firmly before adding the next. Tamp with a steel bar or mechanical compactor. Loose backfill allows pole rocking in wind, which fatigues the wire connections at the hardware.

Hardware Installation

After poles are set and backfill is compacted, install the telephone hardware before stringing wire.

Crossarms: Bolt the wooden crossarm to the pole 150-300 mm below the top. A double-arm arrangement (two arms on opposite sides of the pole) balances the load and allows wire to be placed symmetrically. Single-arm construction is adequate for two pairs or fewer.

Insulators: Screw or bolt insulators to the crossarm pins. Thread insulator pins into the crossarm at the prescribed spacing — 300 mm center-to-center for standard telephone wire. Ceramic or glass insulators with a 73 mm shank are standard. Tighten the pin into the arm firmly; a loose pin will rotate under wire tension, releasing the tie wire.

Through-bolts and lag screws: All hardware attached to poles must use through-bolts (bolts that pass completely through the pole with a nut and washer on both sides) rather than lag screws for any load-bearing application. Lag screws pull out progressively under vibration; through-bolts cannot.

Wire Stringing

String wire from a reel mounted on a vehicle or dragged along by a walking crew. Thread the wire through (not over) each insulator before tying, keeping the wire above the insulator groove until the complete span is strung and tensioned. Stringing the wire over the tops of insulators first makes correcting sag impossible.

Tension the wire to the correct sag (0.6-0.9 meters for 40-meter spans at standard installation temperature) using a wire-straining device or a turnbuckle and block-and-tackle. Measure sag at mid-span with a level and measuring rod. Once sag is correct, tie the wire into the insulator groove with tie wire — wire of the same material and gauge wrapped 3-4 times around the insulator neck and then wrapped around the conductor.

Make dead-end (anchor) ties at both ends of every line section and at all angle poles. A dead-end tie wraps the conductor back on itself 10-12 times and secures both ends to the insulator. The dead-end must be strong enough to hold the full tension of the wire without slipping.

Final inspection: walk the completed line and verify that every insulator is clean (no vegetation contact), all tie wires are complete, sag is consistent along the run, and poles are plumb. Record any deficiencies for immediate correction before service is connected.