Lesson 7 of 8How lifts work
Lift ropes.
The car of a traction lift hangs from steel wire ropes that bend over the sheave on every journey. Here is how those ropes are made, what keeps them safe, how they wear and how engineers decide when to replace them.
How a lift rope is made.
A lift rope is built up in three layers. Steel wires are twisted together into a strand. Several strands are then laid in a spiral around a central core. On many lift ropes the core is made of fibre, a fibre core, which supports the strands, holds lubricant and lets the rope flex. Some ropes have a steel core instead.
Cross-section
Side view
Describe these diagrams
Left: a cross-section through the rope. Eight strands sit in a ring around a fibre core. Each strand has a centre wire, an inner ring of nine small wires and an outer ring of nine larger wires.
Right: a short length of the same rope seen from the side. The strands wind around the rope in a spiral. The distance along the rope for one strand to make a complete turn is the lay length. The diameter is measured across the widest point of the rope.
Rope makers describe a rope by its construction. A common lift rope is 8 × 19 Seale with a fibre core: eight strands of 19 wires each. In a Seale strand, the outer wires are larger, to resist wear where the rope touches the sheave, and the inner wires are smaller, to keep the rope flexible.
Two measurements matter in service. The diameter is measured across the widest point of the rope. The lay length is the distance along the rope for one strand to make one complete turn, roughly six times the rope’s diameter, and it is the length over which engineers count broken wires.
What the rules require.
The law
Under the Lifts Regulations 2016, a car suspended by ropes or chains must have at least two independent ropes or chains, each with its own anchorage, and they must have no joins or splices except where needed to fix them or form a loop.
BS EN 81-20, the standard for new passenger lifts, adds detailed rules for suspension ropes:
- Number: at least two ropes, independent of each other.
- Size: a nominal diameter of at least 8 mm.
- Safety factor: each rope’s minimum breaking load must be at least 12 times the most it carries, with the rated load in the car at the bottom floor. On a traction lift with only two ropes, the factor is 16.
- Bending: every sheave and pulley must be at least 40 times the rope diameter, because tight bends wear ropes faster.
- Rope ends: fixed with wedge sockets, ferrule-secured eyes or swaged terminals that hold at least 80 per cent of the rope’s minimum breaking load.
- Equal tension: an automatic device, often a set of springs, shares the load between the ropes. On a lift with only two ropes, a safety switch stops the lift if one rope stretches abnormally.
Older lifts were built to earlier standards, but the principle is the same: several ropes, each sized with a large margin, so that the set is far stronger than the load it carries.
How lift ropes wear.
Every journey bends the ropes over the sheave and any pulleys, then straightens them again. Over time that bending fatigues the wires, and contact with the sheave grooves wears them. Wear is faster when:
- the ropes bend over many sheaves and pulleys on each journey;
- the sheave grooves are worn, so the ropes sit too deep, are pinched or slip;
- the ropes carry unequal loads because their tensions have not been equalised;
- the ropes have twisted, for example because they were installed badly;
- the ropes are not lubricated correctly;
- the shaft is damp, dusty or exposed to anything that causes corrosion.
SAFed’s LG1 guidance, prepared with the lift industry and described by the Health and Safety Executive as good practice, says the biggest factors in rope life are the number of bends the ropes make and how tight those bends are. That is why the rules set a minimum sheave size. No fixed life can be given, but LG1 advises particular care once ropes are more than ten years old, or where a lift has a history of short rope life.
Lubrication needs balance. Rope makers apply lubricant during manufacture, and LG1 notes that a slightly oily deposit in the sheave grooves is a good sign. Too little lets the ropes dry out and corrode; too much can make them slip on the sheave.
Ropes also stretch. A new set lengthens as the strands bed in, and then more slowly over its life, so engineers shorten the ropes when needed and check the clearances above and below the car and the counterweight.
What engineers look for.
Ropes are examined along their full length, with most attention on the sections that run over the sheave and pulleys most often. These are the signs that matter:
| Sign | What it means |
|---|---|
| Broken wires | Wires fatigue and break, usually on the outside of the strands. Engineers count them over one lay length. |
| Reduced diameter | Wear, internal corrosion or a failing core can make the rope thinner than its nominal diameter. |
| Corrosion | Rust on or inside the rope weakens the wires. LG1 notes that a badly corroded rope cannot be restored by adding lubricant late. |
| Red dust | Fine red dust, sometimes called rouge, coming out of the rope. LG1 lists it among the signs that a rope may be failing. |
| Distorted or displaced strands | A kink, a strand standing proud or a rope that has lost its shape has been damaged and needs assessing. |
| Local damage | A short section that is flattened, indented or thinner than the rest. |
The rope ends are checked too. LG1 says the terminations should be closely examined at every thorough examination for movement, cracking, deterioration, wear and broken wires.
Engineer’s note
LG1 gives figures for judging single-layer ropes with fibre cores running in cast iron or steel sheaves, where there are no national regulations or manufacturer’s instructions to follow. For an 8 × 19 rope, more than 15 broken wires spread across the outer strands in one lay length means the ropes should be replaced, or examined again within a period the competent person sets. More than 30 means they should be discarded immediately. Where the ropes run in ‘U’, ‘V’ or undercut grooves on a traction sheave, a reduction of more than 6 per cent from the nominal diameter is a guide for rejection. The competent person decides how much wear can be tolerated on your lift.
When ropes are replaced.
Rope replacement is planned work. When an engineer or the competent person reports that the ropes are approaching their limit, the replacement can be scheduled in good time, rather than the lift being taken out of service at short notice. LG1 says the latest date for replacement should be given on the report of thorough examination.
LG1 also says that when a suspension rope needs replacing, all the suspension ropes on that lift must be renewed together. A new rope stretches and beds in differently from ropes that have been in service, so a mixed set would not share the load evenly. The sheave grooves are checked at the same time, because worn grooves would quickly damage new ropes, and the sheave may need regrooving or replacing.
Once the new ropes are fitted, their tensions are equalised, the clearances are checked and the lift is tested before it returns to service. The date of replacement is recorded, so the competent person can see how old the ropes are at later examinations.
Our lift repairs page explains how we plan and carry out work like this.
Belts and smaller ropes.
Not every modern lift hangs from conventional steel wire ropes. Some use flat coated steel belts, with steel cords inside a polyurethane coating. Others use ropes thinner than the usual 8 mm minimum, ropes with a polymer coating, ropes made from aramid fibre or a sheave smaller than 40 times the rope diameter.
LG1 says these should be examined for wear or damage at every thorough examination, as conventional ropes are. Because the steel inside a belt or a coated rope cannot be seen, an automatic monitoring device may be used as well, and the competent person may call for a supplementary test. The manufacturer’s manuals and guidelines set how that testing is done and how often. If your lift has belts or small ropes, ask your maintenance provider how they are inspected and what the manufacturer specifies.
Safety first
Never open lift doors with a release key, enter a lift shaft or pit, or try to free trapped passengers unless you are trained and authorised to do so. If someone is trapped, use the alarm or call your maintenance provider. If anyone is in danger, call 999.
Check your understanding.
Three quick questions on this lesson. Choose an answer to check it, or open the answer below each question.
-
What is a strand?
Show the answer
B. A group of wires twisted together; several strands make up the rope. Wires are twisted together to make a strand, and several strands are laid around a core to make the rope. A common lift rope has eight strands of 19 wires each.
-
What is the lay length of a rope?
Show the answer
B. The distance along the rope for one strand to make a complete turn. The lay length is how far along the rope one strand travels in one full turn around it. Engineers count broken wires over one lay length when they judge a rope’s condition.
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How many suspension ropes must a new rope-suspended lift have, at the least?
Show the answer
B. Two independent ropes. The Lifts Regulations 2016 and BS EN 81-20 both require at least two independent ropes. In practice many traction lifts have more.
Sources.
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Related reading
Concerned about the ropes on your lift?
Talk to an engineer about rope condition, replacement and what the work involves.
Common questions.
Quick answers to common questions about this topic.
How long do lift ropes last?
There is no fixed life. It depends on how many journeys the lift makes, how many times and how tightly the ropes bend over sheaves and pulleys, the condition of the sheave grooves, rope tension, lubrication and the conditions in the shaft. SAFed’s LG1 guidance advises particular care once ropes are more than ten years old, but each set is judged on its condition rather than on age alone.
What are the signs that lift ropes need replacing?
Engineers look for broken wires, a reduction in rope diameter, corrosion, red dust coming from the rope, distorted or displaced strands and local damage such as flattening. Passengers rarely notice anything, which is why rope condition is checked at maintenance visits and at thorough examinations.
Can one lift rope be replaced on its own?
Not as a rule. SAFed’s LG1 guidance says that when a suspension rope needs replacing, all the suspension ropes on that lift must be renewed together. A new rope stretches and beds in differently from ropes that have been in service, so a mixed set would not share the load evenly.
Do all lifts use steel wire ropes?
Most traction lifts do. Some newer lifts use flat coated steel belts, ropes thinner than 8 mm or ropes with a polymer coating. They are examined at every thorough examination like any other suspension, but the manufacturer’s guidelines set how they are tested, because they cannot always be judged by counting broken wires.