Wire Rope Breaking Strength

Wire rope by diameter: breaking strength pages

Eight inch sizes have a page of their own. Each one lists the published minimum breaking load for every construction made in that diameter, the weight per metre, and the safe working load at 5:1, 6:1 and 8:1. The table below indexes them.

A dash means the construction is not made in that diameter: 6x36 begins at 8 mm, 6x19 at 14 mm, and 7x19 stops at 14 mm. The millimetre column is the inch size converted, not the catalogue diameter - stock is rounded, so 1/8 inch is made as 3 mm and 3/16 inch as 5 mm - and each page names the diameter of every row it lists, including the sizes where the constructions differ.

All wire rope: wire rope range | construction guide | which rope to choose

From MBL to Safe Working Load

The safe working load (SWL) divides the breaking load by a safety factor: SWL = MBL ÷ safety factor.

Many lifting applications use a factor of 5, though the factor that applies to your job depends on the standard and jurisdiction governing it - always confirm against the regulation in force before lifting.

Worked example: a 6x19 IWRC rope at 20 mm in 1770 grade has an MBL of 252 kN. Divided by 5, that is about 50.4 kN, or roughly 5.1 tonnes.

Two practical notes. Terminations reduce rope capacity - a splice or fitting is rated by its own efficiency, not the rope's. And in service, wear, broken wires and corrosion reduce strength over time, so inspection and retirement follow the applicable standard rather than the original table.

Using the Tables

• Match all three: construction, diameter and grade - the same size in a different construction carries a different load.
• Then divide by your safety factor to reach the working load for the application.
• Account for terminations: fittings and splices are rated by their own efficiency.
• Inspect in service: wear, broken wires and corrosion reduce capacity; follow the applicable retirement standard.

Need the full table for a construction? See the construction guide for how the patterns behave and the core types guide for FC and IWRC differences,

browse the wire rope range, or send the construction, diameter and grade you need to admin@greenlogy.cn and we will return the exact figures.

Small Diameter Wire Rope: 1/8 in to 1/4 in

Below 5/16 in we supply 7x19 rope at 1570 MPa - the construction used for aircraft cable and control runs, where flexibility matters more than ultimate strength. A 1/8 in rope is 3 mm nominal and breaks at 5 kN; 1/4 in is 6 mm at 20 kN.

7x19 wire rope.

Using the Inch Chart

• Inch on the enquiry, metric on the order: quote the stock diameter from the second column, and keep the inch size in the specification so both parties read the same rope.
• Both grades are listed. At the same diameter 1960 MPa carries about 11% more load than 1770, so compare the two MBL columns before choosing.
• Divide by the safety factor to reach the working load: a 5:1 factor on the 1/2 in row (107 kN at 1770 MPa) leaves about 21 kN, or roughly 2.2 tonnes.
• Use the weight columns to size the drum, the transport and the support structure - they are per metre of rope only.

For how the constructions differ see the construction guide, for fiber core against steel core the core types guide, and for every diameter in stock the wire rope range.

What reduces strength between the table and the lift

An MBL assumes a new rope, tested straight, with both ends gripped in a way that does not cut into it. Four things erode that figure in service, and all four are visible on inspection.

• Terminations: a splice or fitting carries its own efficiency rating, and that rating, not the rope MBL, sets the capacity of the assembly.
• Bending: every pass over a sheave or drum bends the wires. A sheave that is small for the rope diameter concentrates that bending and shortens life - which is why the construction matters as much as the size.
• Wear and broken wires: abrasion removes metal from the outer wires, and a broken wire stops carrying its share. Both lower the remaining strength before the rope looks worn out.
• Corrosion: moisture inside the strands attacks wires that cannot be seen. Galvanizing slows it; it does not stop it.

Retirement is decided by the standard that governs the installation - measured broken wires, loss of diameter, corrosion - not by comparing the rope with its original table figure. Nothing here replaces that standard.

Which table to read: the reference table gives MBL by construction and grade at a few diameters; the inch chart converts a nominal inch size to the metric stock diameter and lists the constructions that reach it; the small-diameter table covers 1/8 in to 1/4 in; and the weight table gives mass per metre and per foot for estimating reel loads. Where a size is not listed, the wire rope range is the authority - every product page tabulates each diameter it is made in.

The pattern behind a figure is explained in the construction guide; the difference between fiber and steel cores is in the core types guide; and the rotation-resistant wire rope guide covers the ropes built not to turn. Send the construction, diameter and grade to admin@greenlogy.cn and we will return the exact figures.