Cross-arms for 0.4–10 kV Lines: TM and TN Types, Reading the Designation

TN and TM: what is the difference

• TN: low-voltage cross-arms for 0.4 kV overhead lines;
• TM: high-voltage cross-arms for 10 kV lines. The size and mass of the marks in the TM 1 to TM 31 range depend on the number and arrangement of the wires.

Both types are made to the standard albums of series 3.407.1-143 and 3.407.1-136 of the Selenergoproekt institute. The same albums cover the caps, plates, extensions, clamps and bolts for these poles.

How to read a cross-arm mark

A mark is the letters TM or TN plus a number from the standard album’s range: TM 1, TM 24, TM 30. Numbers in the range usually differ in size and mass. For each one the album gives a drawing reference (for example, “3.407.1-143.8.1” for TM 1) and the mass in kilograms.

The page Fittings for 0.4–10 kV Lines has the full table of TM marks with the mass of each.

Material and corrosion protection

TM and TN cross-arms are welded or bolted structures of angle or plate steel, made to the dimensions of the specific number in the standard album. Corrosion protection is either BT-577 varnish or, by special order, hot-dip galvanising to DSTU EN ISO 1461:2024. Say which one you need when you order.

Compatibility with reinforced-concrete poles

Under the standard albums, TM and TN cross-arms are designed for standard reinforced-concrete poles of 0.4–10 kV lines (SV-95, SV-105 and similar). They are fixed with clamps through holes in the pole. The geometry of each mark is tied to the cross-section of these poles, which is why a cross-arm is chosen by pole type and line voltage rather than by how it looks.

How to order a cross-arm

The simplest way is to name the mark from the standard album, say TM 12, or the type of pole the set is for. If you do not know the mark, send the reinforced concrete pole type and the line voltage, and we will pick the cross-arm.

Mass of TM cross-arms: from 10 to 45 kg

Mass drives the transport calculation and the cost of galvanising, which is charged per kilogram. Below is a selection from the table on the page Fittings for 0.4–10 kV Lines: the lightest mark, the heaviest and a few in between.

The lightest mark in the table is TM 9 (10.1 kg) and the heaviest is TM 20 (45.0 kg): TM 20 is more than four times as heavy as TM 9. TM 23 and TM 31 are made to the same drawing but have different masses, so an order should state the mark, not the drawing number.

Example: reading a request for 30 cross-arms

Take this request: “30 pcs TM-12 for a 10 kV line on SV-105 poles, galvanised”. Here is what follows from it:

• “TM-12” reads as the mark TM 12: TM-12, TM12 and TM 12 are the same cross-arm. TM means a cross-arm for 10 kV lines, so the mark fits the voltage in the request;
• one cross-arm weighs 33.4 kg, so thirty weigh 30 × 33.4 = 1,002 kg, about 1 t; transport and galvanising are planned from that figure;
• SV-105 is a pole 10.5 m long. Before manufacture we check that the mark suits the pole type and the wire arrangement;
• what is missing: whether the pole is a suspension or a tension one, whether clamps and bolts are needed, the required zinc thickness and the delivery point. We clarify these in our reply.

Pre-order checklist for cross-arms

• line voltage: 0.4 kV for TN, 10 kV for TM;
• pole type: SV-95, SV-105 or another. The number in the designation is the length in decimetres (9.5 m, 10.5 m);
• where the pole stands on the route: suspension, tension, angle or terminal (see Power Line Pole Types by Purpose);
• the mark from the standard album and the quantity; if you do not know the mark, the wire arrangement;
• clamps Kh 33–Kh 36 and bolts B 1, B 5, B 6 are separate items in the product range, so list them if you need them;
• coating: BT-577 varnish or hot-dip galvanising to DSTU EN ISO 1461:2024. The minimum zinc thickness depends on the steel thickness: for steel over 3 up to 6 mm the mean thickness is at least 70 µm (see Zinc Coating Thickness);
• shipping: from stock or delivered to site.

Common cross-arm ordering mistakes

• choosing a cross-arm by appearance or by drawing number. The drawing number does not always match the mark number: TM 20 is made to drawing 3.407.1-143.8.19, TM 30 to 3.407.1-143.8.70;
• swapping TN for TM, or the reverse, without approval: they are for different voltages;
• ignoring the mass: the same number of pieces in different marks can give very different batch masses;
• not stating the coating, BT-577 varnish or hot-dip galvanising: without it the order cannot be priced accurately;
• ordering the cross-arms alone when installation needs a complete set with clamps and bolts.

TM marks by mass: three groups

The catalogue table has 26 marks of the TM 1 to TM 31 range. By mass they fall into three groups, which helps to estimate the weight of a batch before the exact selection. The middle group is the largest: 14 marks out of 26.

Mass is taken from the standard drawings, before galvanising. The full table with drawing numbers is in the catalogue of fittings for 0.4–10 kV lines.

How to match marks to your specification

The same cross-arm appears in designs as “TM-3”, “TM3” and “TM 3”: for us it is one mark. Drawing numbers in the album are trickier.

Three pairs of marks are made to a shared drawing: TM 1 and TM 24 (3.407.1-143.8.1), TM 12 and TM 19 (3.407.1-143.8.12), TM 23 and TM 31 (3.407.1-143.8.22). The mass within a pair may differ, for example TM 12 weighs 33.4 kg and TM 19 weighs 38.0 kg. So the drawing number does not identify the mark, and an order should name the mark itself.

Marks TM 25 to TM 29 are not in the catalogue table. If they appear in your specification, send us the drawing from the album and we will make the cross-arm to it.

Example of a specification for a set

An illustrative request for a stretch of a 10 kV line: what to write and how to work out the weight. The contents of the set are decided by the line design; the table only shows the method. In the example each cross-arm comes with one pole head, two clamps and two bolts: that is 35.7 kg per set (23.0 + 7.3 + 2 × 2.0 + 2 × 0.7).

Masses are from the catalogue, before galvanising: after hot-dip galvanising the weight rises by the mass of the coating. Galvanising is charged by mass, so you can put the total and the dimensions into the galvanising cost calculator.

Coating, lead time and shipping

On request we galvanise in our own bath of 13,000 × 1,600 × 3,200 mm; there is no minimum order and TM cross-arms fit the bath.

The typical lead time is 3–4 weeks if the item is not in stock; we give the exact date after pricing your specification. We ship from stock or deliver to site anywhere in Ukraine.