Power Line Pole Types by Purpose: Suspension, Tension, Angle, Terminal

Suspension poles

Suspension (intermediate) poles stand on straight sections of the route and only support the wires and cables through insulator strings or clamps — they do not take the longitudinal tension of the wires, only the wire weight and the wind load across the route. This is the most common type: 80–90% of all poles on a line are suspension poles, so reducing structure weight matters most for them.

Tension poles

Tension (anchor) poles rigidly fix the wires (with tension strings or clamps) and take the difference in wire tension on both sides — so they are designed for a much greater longitudinal load than suspension poles and are built structurally stronger. Tension poles are usually placed at crossings of structures, roads, rivers and other obstacles, and wherever the wire grade, cross-section or number changes — at these points the line must hold even if a wire breaks on one side.

Angle poles

Angle poles stand at turning points of the route and take the resultant force from the change in wire direction. Depending on the turning angle:

• suspension angle poles — for small turning angles, 15–30°: structurally closer to suspension poles, reinforced for the side load;
• tension angle poles — for turning angles above 30°: designed as tension poles, since the load from the turn approaches the load from a one-sided wire break.

Terminal (dead-end) poles

Terminal poles stand at the very start and end of the line, where it connects to a substation switchyard or another facility. Like tension poles, they take the one-sided tension of all wires and cables, so their design is similar to tension poles.

Transposition poles

On long high-voltage lines the phase wires are periodically swapped (transposed) to equalise the mutual inductance and capacitance between phases and reduce voltage asymmetry. The pole where this phase reconnection is carried out is called a transposition pole — structurally a type of tension pole with extra cross-arms for the reconnection scheme. We design such poles individually for the specific transposition scheme.

Normal and light tension poles, transposition, crossing poles

Under the Rules for the Arrangement of Electrical Installations (PUE), 2026 edition, cl. 2.5.80 and 2.5.134, tension poles are either normal or light in design, depending on the failure case they are calculated for. For aluminium wires and PS and PMS steel wires of any cross-section, and for steel-aluminium and aluminium-alloy wires up to 150 mm², a normal pole is calculated for the break of two phases in one span, a light pole for one phase. For steel-aluminium and heat-treated aluminium-alloy wires of 185 mm² and above, a normal pole is calculated for the break of one phase. Separately, a tension pole is calculated for the break of one earth wire.

Under PUE (2026 edition), cl. 2.5.8, on lines of 110 kV and above longer than 100 km one full cycle of phase transposition is required to limit current and voltage asymmetry. Incomplete cycles, segments of different lengths and more cycles are permitted if the calculated asymmetry stays within 0.5% for voltage and 2% for negative-sequence current.

Under PUE (2026 edition), the requirements for poles that limit a crossing span depend on what the line crosses; the designer takes the final values from the current text of the PUE.

Comparing pole types

Classification by other criteria

Besides purpose, power line poles are classified by other, independent criteria: by material (wood, reinforced concrete, steel multi-sided and lattice — compared in Transmission Poles: Multi-Sided, Lattice or Reinforced Concrete) and by circuit count (single-circuit and double-circuit — see Double-Circuit Power Line Poles).

Why the pole type matters for the calculation

Pole type and purpose are among the main inputs for design: tension, tension-angle and terminal poles withstand much greater loads than suspension poles, so they come out heavier and more expensive than suspension poles of the same height. Specifying the correct type in the technical specification gives an accurate calculation instead of a margin added “just in case”.

Pole height also depends on the line’s voltage class: the ranges for each class 35–750 kV are in the article Transmission Pole Height by Voltage Class.

How pole types are placed along the route

The type of each pole is set from the route plan and profile, not by guesswork. The sequence is roughly this:

• terminal poles go at the start and end of the line; where an overhead line changes over to a cable, a terminal pole or a transition point is used (PO-KV for 35–110 kV lines);
• every noticeable turning point gets an angle pole: a suspension angle pole for moderate angles (15–30°), a tension angle pole for angles above 30°; a very slight change of direction, a few degrees, can also be taken by an ordinary suspension pole, which the calculation confirms;
• crossings of roads, rivers and other lines, and places where the wire grade or cross-section changes, usually get tension poles; the final choice of type rests with the crossing design;
• the remaining straight sections between these points are filled with suspension poles.

Tension poles also divide the line into tension sections and limit how far a failure spreads: after a wire breaks, the difference in tension is taken by a tension pole, not by a chain of suspension poles. Under PUE (2026 edition), cl. 2.5.135, on lines above 1 kV the distance between tension poles must not exceed: 3 km on lines up to 20 kV with suspension insulators (including 6–10 kV lines with such insulators, see 6–10 kV poles); 1.5 km (ice regions 1–3) or 1 km (regions 4 and above) on lines up to 35 kV with pin insulators; 10 km on new lines of 35 kV and above with suspended conductors, or 5 km in hard-to-reach terrain and in especially difficult natural conditions.

Example: pole layout on a 10 km route

Assumed data, not a real project: a 10 km route, spans of 250 m, turns of 20°, 25° and 45°, and one road crossing on two tension poles (one on each side). That gives 10,000 ÷ 250 = 40 spans, so 41 poles.

The 250 m span is an assumption; on 6–10 kV lines spans are shorter, so there would be more poles. The 45° angle does not exceed what our tension angle poles for 110 kV allow.

Check: 2 + 2 + 1 + 2 + 34 = 41. Suspension poles: 34 ÷ 41 ≈ 83%, within the typical 80–90%. The example is simplified: the real layout comes from the route design.

What to state in the request and which mistakes to avoid

In the request, state the lengths of adjacent spans, the grade and cross-section of the wires and earth wire, and the wind and ice regions (loads on power line poles); for key poles, also the turning angle in degrees at each point and why a tension pole is needed there. The most common mistakes:

• ordering only suspension poles without singling out the key poles: there are few of them, but they carry more load;
• not stating the turning angles: with 30° as the dividing line, poles for 28° and 33° belong to different types, so refining the route can change the type and cost; the maximum permitted angle also depends on the pole series;
• not allowing for heavier wires later: a pole is designed for specific wires, so switching to heavier wire means recalculation.