wire rope breaking strength vs working load in stock

In the shipping industry, items like winch straps and ratchet straps use two common measuring metrics. One of them is the working load limit, while the other is the strap’s break strength. At first glance, it’s understandable why some people might mix the two up. They kind of mean the same thing, don’t they? In this article, we’ll look at break strength vs. working load limit, explaining the differences and why those differences are so important.

We’ll start with break strength since this term is more self-explanatory than the other. Put simply, the break strength of a piece of rigging is the amount of weight that would cause the weakest part of the rigging to fail. Ideally, you’ll never actually test a rigging’s break strength, as the weight of the loads they’ll carry will usually be much lower than this limit.

If a cargo strapping system consists of fittings, webbing, and a tensioning device that all have a break strength of 12,000 pounds, that strapping system’s break strength would be 12,000. However, if one of those components (the fittings, webbing, or tensioning device) has a lower break strength of 9,000 pounds, then the entire strapping system has a break strength of 9,000 instead.

The difference in break strength vs. working load limit comes into play when you understand the concept of the working load limit means. A rigging’s working load limit is the amount of weight that it can handle under normal conditions. This number will always be smaller than the break strength, and that piece of rigging should never hold more than its working load limit.

The working load limit of a rigging system is equal to 1/3 the amount of the break strength. As such, a strapping system with a working load limit of 5,000 pounds has a break strength of 15,000 pounds. Remember, the working load limit will determine how much you should allow the system to hold, not the break strength.

Logistick makes our products able to stand the test of time. Our cargo strapping systems have all undergone extensive testing for both working load limit and break strength, so you can rest easy and trust the numbers you see. If you have any questions about our products or how they work, please give us a call. We’ll be happy to help you out.

It’s rare for a week to go by here at Industrial Wire Rope without discussions about tensile strength or working load limit. We take it for granted that most people in our industry know there is a difference in the meaning of these terms. Yet, these terms and others are highly interrelated, and we thought an overview of them on one page might be a helpful reference. For those who want to dive deeper into the definitions and how they apply on the job, we’re also providing links to sources with additional information.

Let’s start with Tensile Strength. As we described in a post from 2017, “Tensile strength is a measurement of the force required to pull something such as rope, wire, or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress that it can take before failure, for example breaking.”

In our immediate world, tensile strength is the force required to break the ropes we offer. Tensile strength is determined by testing. Obviously, it is different for every type of rope, being a function of the material and construction of each type.

Although tensile strength is a definitive quantity measuring the force required to break a rope, working load limit is a measure that takes a wide range of variables into account. And always, the tensile strength of a material is greater than the recommended working load limit.

The working load limit provides consideration for factors such as the abrasion, friction and rubbing the rope is subjected to, the variance in temperature extremes it is exposed to, harmful substances that may come into contact with it, age, and even knots in the rope. Working load limit is defined as “the maximum load which should ever be applied to the product, even when the product is new and when the load is uniformly applied”.

Working load limit is always a fraction of tensile strength, allowing for a generous margin of safety. For wire ropes, it’s common for the working load limit to be set at 20% of tensile strength. However, you generally don’t have to be concerned about doing the math on your own. Rope manufacturers typically mark the working load limit on the products, so the information should be readily available to you.

When it comes to rigging like ratchet straps, winch straps, and just about any other type of strap in the industry, working load limit (WLL) and breaking strength are commonly used measuring metrics.

Every piece of load-bearing wire or rigging equipment carries its own working load limit and break strength rating. These numbers let the user know how much weight that piece of rigging is capable of securing. Though they are usually clearly stated, there is often some confusion about what the two terms mean.

WLL refers to the maximum allowed weight that a piece of rigging can handle under normal conditions. For instance, a winch strap with a WLL of 6,000 pounds should not be used to secure any load above that weight, as it exceeds what it is rated for. WLL is 1/3 of the breaking strength rating, therefore a strap with a WLL of 6,000 pounds would have a breaking strength of 18,000 pounds.

For example, if a ratchet strap is made with end fittings, webbing, and a ratchet that are all rated for 10,000 pounds breaking strength, the overall strength of the product is 10,000 pounds. If any component of the ratchet strap has a lower breaking strength though, the break strength of the unit drops to the rating of the weakest component.

It is critical to understand the differences between the two figures and to make sure that any time you are securing a load, you do so with capable rigging. A failure could not only be costly, but dangerous as well.

When it comes to choosing the right rope for the job, it helps to know what variables are at play, like working load, rope tension, and tensile strength of rope. But exactly what is working load, what is tensile strength, and why does rope tension matter? Keep reading to find out!

Tension isthe pulling forceacting along a stretched, flexible connector like aRope. If you want to hang, pull, swing, or support an object with a rope, you must first create enough tension in the rope to the point where the rope is pulled tight enough to cause the object to move. This tension created by the pulling of the rope in the opposite direction of the object you’re trying to move is calledtension force.

When a rope supports an object’s resting weight, the rope’s tension is equivalent to the object’s weight. The simplest way to determine the tension in a rope is using the followingformula:

It’s important to note that rope tension can change based on several variables, and the example above is a simple breakdown of how to find the tension of a non-moving object being pulled straight and not at an angle.

Simply put, tensile strength is the resistance of a material to breaking under tension. In other words, tensile strength is the stress in which a rope can take before breaking or failing. Another common name for the tensile strength of rope is breaking strength.

The tensile strength of a rope can vary based on the thickness, material, and style (braided vs. twisted). Also,Knotsthat are tied into the rope can affect tensile strength. For instance, a ⅜” thickDouble Braid Nylon Docklineboasts a tensile strength of 4,200 pounds, while the same dockline in a ½” thickness can support 7,400 pounds before breaking.

It’s important to recognize that the maximum tensile strength of a rope is not the same weight you should be applying to said rope while expecting it to perform safely. For this, you should limit the weight you plan to support based on the rope’s working load.

Working load is the amount of weight a rope cansafely support without fear of breaking. As previously mentioned, working load is always going to be less weight than tensile strength weight. In fact, most ropes have a working load between 15 to 25% of the rope’s tensile strength. Working load and tensile strength will change based on whether or not you have knots. If you are wondering whether your rope product has an adequate working load to support your needs, contact the manufacturer directly.

No matter what your rope andCordproduct needs may be, SGT KNOTS is sure to have the perfect solution to help you get the job done safely and effectively. Visit SGT KNOTS onFacebookandInstagram, andPinteresttoday to see how our rope products are used every day, Or if you need some inspiration of your own, visit theSGT KNOTS Blog!

Have you picked up a ratchet strap and saw numbers labeled on the strap, and wonder what they mean? Chances are you"re reading the working load limit or break strength. Every piece of load-bearing equipment states these requirements to let you know how much weight that piece of rigging is capable of securing.

When it comes to securing fragile or heavy loads, it is crucial that the product can secure the load without breaking. Although these terms are normally stated, there is confusion about what these terms mean. Read on below to learn what working load limit, break strength, and safety factor mean.

Many people ask about the working load limit, and this is a term to not mix up with breaking strength. Abbreviated as WLL, it is the rating that should never be exceeded when using a product like a ratchet strap. Before using a piece of load-bearing equipment, always make sure to look at the working load limit before use as it is the maximum allowable loading force.

Something to keep in mind is the working load limit is always 1/3 of the breaking strength. So if a ratchet strap has a breaking strength of 15,000 pounds, then the strap will have a working load limit of 5,000 pounds.

The break strength is equally as important as the WLL. The break strength also refers to the point at which your load-bearing equipment will fail. It is expressed in pounds and/or kilograms, and will actually fail if you go over the required amount.

When a ratchet strap is made with webbing, end fittings, and a ratchet all with a 10,000-pound breaking strength, then the break strength of the overall product will stay 10,000 pounds. However, if the same strap has a ratchet with an 8,000-pound break strength, then that would reduce the product"s strength to 8,000.

Safety factor, also known as Design Factor, determines the ratio between the working load limit and break strength. The working load limit"s rating should never exceed when using a sling or tiedown, and this safety factor provides an allowance for shock loading, G force, and other unforeseen factors.

When selecting a ratchet strap, lifting sling, shackle, or any other product, select the product that has suitable characteristics for the type of load, environment, and attachment to the vehicle.

At US Cargo Control, we want you to be safe when securing heavy loads. If you have any questions about the safety requirements, give our team a call at 800-404-7068 or email us at customerservice@uscargocontrol.com.

The tensile strength is the load at which a new rope, tested under laboratory conditions, can be expected to break. Rope strength is the approximate average for new rope tested under ASTM test method D-6268. To estimate the minimum tensile strength of a new rope, reduce the approximate average by 20%. Age, use and the type of termination used, such as knots, will lower tensile strengths significantly.

One area of misunderstanding that needs to be brought to the surface is the proper interpretation of rope strength, appropriate usage and care. Let"s start by defining two important terms: "tensile strength" and "working load". Tensile strength is the average strength ofnewrope under laboratory conditions. This is determined by wrapping the rope around two large diameter capstans and slowly adding tension to the line until it breaks. The manufacturer"s recommended working load is determined by taking the tensile strength and dividing it by a factor that more accurately reflects the maximum load that should be applied to a given rope to assure a comfortable safety margin and longevity of the line. Of course that factor varies with the type of fiber and the weaving construction. There are however always exceptions, most notably the fact that rope is susceptible to degradation and damage in numerous ways that are not controllable by the manufacturer.

It may surprise you to find out that the working load for most kinds of rope is between 15% and 25% of the tensile strength. Now consider the fact that any time you tie a knot in a rope you effectively cut the tensile strength in half. The knot when tensioned cuts the line. While certain kinds of knots damage the line less than others, the 50% loss of tensile strength is a good general rule to live by. Research has shown that the figure 8 knot reduces the tensile strength by approximately 35% instead of 50% for other common knots tested.

At Ravenox, we use a third-party mechanical services company to test the failure point or break strength of our ropes. There are two common types of breaks: the sharp break and the percentage break. The sharp break is referred to the measurement when load or force drops by 5% from its peak load measurement. A percentage break is another form of break and is generally determined by the sample material and its relationship to load degradation from a peak load measurement. We measure the percentage break.

The use of rope for any purpose results in friction, bending and tension. All rope, hardware, sheaves rollers, capstans, cleats, as well as knots are, in varying degrees, damaging to ropes. It’s important to understand that rope is a moving, working, strength member and even under the most ideal conditions will lose strength due to use in any application. Maximizing the safety of rope performance is directly related to how strength loss is managed and making sure ropes are retired from service before a dangerous situation is created. Ropes are serious working tools and used properly will give consistent and reliable service. The cost of rope replacement is extremely small when compared to the physical damage or personnel injury that can result from using a worn out rope.

There are basically three steps to consider in providing the longest possible service life for ropes, the safest conditions and long range economy: Selection, Usage and Inspection.

Selecting a rope involves evaluating a combination of factors. Some of these factors are straight forward, like comparing rope specifications. Others are less qualitative, like color preference or how a rope feels while handling. Cutting corners, reducing design factors, sizes or strengths on an initial purchase creates unnecessary replacements, potentially dangerous conditions and increased long term costs. Fiber and construction being equal, a larger rope will outlast a smaller rope, because of greater surface wear distribution. By the same token, a stronger rope will outlast a weaker one, because it will be used at a lower percentage of its break strength and corresponding Work Load Limit with less chance of overstressing. The following factors should be considered in your rope selection: Strength, Elongation, Firmness, Construction and Abrasion.

When given a choice between ropes, select the strongest of any given size. A load of 200 pounds represents 2% of the strength of a rope with a 10,000 Lbs. breaking strength. The same load represents 4% of the strength of a rope that has a 5,000 Lbs. breaking strength. The weaker rope will work harder and as a result will have to be retired sooner. Braided ropes are stronger than twisted ropes that are the same size and fiber type.

Please note that the listed break strengths are average break strengths and do not consider conditions such as sustained loads or shock loading. Listed break strengths are attained under laboratory conditions. Remember also that break strength is not the same as the Work Load Limit.

It is well accepted that ropes with lower elongation under load will give you better control. However, ropes with lower elongation that are shock loaded, like a lowering line, can fail without warning even though the rope appears to be in good shape. Low elongating ropes should be selected with the highest possible strength. Both twisted ropes and braided ropes are suitable for rigging. Size for size, braided rope has higher strength and lower stretch than a twisted rope of similar fiber. See page 390 for additional information on rope elongation.

Select ropes that are firm and hold their shape during use. Soft or mushy ropes will snag easily and abrade quickly causing accelerated strength loss.

Rope construction plays an important role in resistance to normal wear and abrasion. Braided ropes have a basically round, smooth construction that tends to flatten out somewhat over the bearing surface. Flattening distributes wear over a much greater area, as opposed to the crowns of a three strand or to a lesser degree, an eight strand rope.

All rope will be severely damaged if subjected to rough surfaces or damaging edges. All rope must be protected against damaging or abrasive surfaces. Wire rope will score and gouge chocks and bitts creating cutting edges that can damage synthetic ropes. Chocks, bitts, drums and other surfaces must be kept in good condition and free of burrs and rust. Weld beads on repaired capstans, fairleads, etc., are equally damaging, unless dressed down smoothly. Pulleys must be free to rotate and should be of proper size to avoid

Avoid using a rope that shows signs of aging and wear. If in doubt, do not use the rope. Damaged rope must be destroyed to prevent any future use. No visual inspection can be guaranteed to accurately and precisely determine the residual strength of the rope. When fibers show wear in any area, the damaged area must be removed and the rope should be re-spliced or replaced. Check regularly for frayed or broken strands. Pulled strands should be rethreaded into the rope if possible. A pulled strand can snag on a foreign object during usage. Both outer and inner rope fibers may contribute to the strength of the rope. When either is worn the rope is naturally weakened. Open the strand of the rope and inspect for powdered fiber, which is one sign of internal wear. A heavily used rope will often become compacted or hard, which indicates reduced strength. The rope should be discarded and made unusable if this condition is detected. See pages 395 and 396 for additional inspection information.

New rope tensile strength is based upon tests of new and unused spliced rope of standard construction in accordance with Samson testing methods, which conform to Cordage Institute, ASTM and OCIMF test procedures. It can be expected that strengths will decrease as soon as a rope is put into use. Because of the wide range of rope use, changes in rope conditions, exposure to the many factors affecting rope behavior and the possibility of risk to life and property, it is impossible to cover all aspects of proper rope applications or to make generalized statements as to Work Load Limits.

Work Load Limits are the load that a rope in good condition with appropriate splices in non-critical applications is subjected to during normal activity. They are normally expressed as a percentage of new rope strength and should not exceed 20% of the stated break strength. Thus, your maximum Work Load Limit would be 1/5 or 20% of the stated break strength.

A point to remember is that a rope may be severely overloaded or shock loaded in use without breaking. Damage and strength loss may have occurred without any visible indication. The next time the rope is used under normal Work Loads and conditions, the acquired weakness can cause it to break.

Normal Work Load Limits do not cover dynamic conditions such as shock loads or sustained loads, nor do they apply where life, limb or property are involved. In these cases a stronger rope must be used and/or a higher design factor applied.

Normal Work Load Limits are not applicable when rope is subjected to dynamic loading. Whenever a load is picked up, stopped, moved or swung there is increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater the increase in the dynamic loading. In extreme cases, the force put on the rope may be two, three or many more times the normal Work Load involved. Examples of dynamic loading would be: towing applications, picking up a load on a slack line or using a rope to stop a falling object. Dynamic loading affects low elongation ropes like polyester to a greater degree than higher elongation, nylon ropes. Dynamic loading is also magnified on shorter length ropes when compared to longer rope lengths. Therefore, in all such applications, normal Work Load Limits do not apply.

IMPORTANT NOTE: Many industries are subject to state and federal regulations for Work Load Limits that supersede those of the manufacturer. It is the responsibility of the user to be aware of and adhere to those laws and regulations.

Work Load Limits as described do not apply when ropes have been subjected to shock loading. Whenever a load is picked up, stopped, moved or swung, there is an increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater this increase in force will be. The load must be handled slowly and smoothly to minimize dynamic effects. In extreme cases, the force put on the rope may be two, three or even more times the normal Work Load involved. Examples of shock loading are picking up a tow on a slack line or using a rope to stop a falling object. Therefore, in all applications such as towing lines, life lines, safety lines, climbing ropes, etc., design factors must reflect the added risks involved. Users should be aware that dynamic effects are greater on a low elongation rope such as manila than on a high-elongation rope such as nylon and greater on a shorter rope than on a longer one.

The shock load that occurs on a winch line when a 5,000 Lbs. object is lifted vertically with a sudden jerk may translate the 5,000 Lbs. of weight into 30,000 Lbs. of dynamic force, which could cause the line to break. Where shock loads, sustained loads or where life, limb or valuable property is involved, it is recommended that a much higher design factor than 5 be used.

Remember, shock loads are simply a sudden change in tension, from a state of relaxation or low load to one of high load. The further an object falls, the greater the impact. Synthetic fibers have a memory and retain the effects of being overloaded or shock loaded. Ropes that have been shock loaded can fail at a later time, when used within Work Load Limits.

Rope strength is a misunderstood metric. One boater will talk about tensile strength, while the other will talk about working load. Both of these are important measurements, and it’s worth learning how to measure and understand them. Each of these measurements has different uses, and here we’re going to give a brief overview of what’s what. Here’s all you need to know about rope strength.

Each type of line, natural fiber, synthetic and wire rope, have different breaking strengths and safe working loads. Natural breaking strength of manila line is the standard against which other lines are compared. Synthetic lines have been assigned “comparison factors” against which they are compared to manila line. The basic breaking strength factor for manila line is found by multiplying the square of the circumference of the line by 900 lbs.

As an example, if you had a piece of ½” manila line and wanted to find the breaking strength, you would first calculate the circumference. (.5 X 3.14 = 1.57) Then using the formula above:

To calculate the breaking strength of synthetic lines you need to add one more factor. As mentioned above, a comparison factor has been developed to compare the breaking strength of synthetics over manila. Since synthetics are stronger than manila an additional multiplication step is added to the formula above.

Using the example above, letÂ’s find the breaking strength of a piece of ½” nylon line. First, convert the diameter to the circumference as we did above and then write the formula including the extra comparison factor step.

Knots and splices will reduce the breaking strength of a line by as much as 50 to 60 percent. The weakest point in the line is the knot or slice. However, a splice is stronger than a knot.

Just being able to calculate breaking strength doesn’t give one a safety margin. The breaking strength formula was developed on the average breaking strength of a new line under laboratory conditions. Without straining the line until it parts, you don’t know if that particular piece of line was above average or below average. For more information, we have discussed the safe working load of ropes made of different materials in this article here.

It’s very important to understand the fundamental differences between the tensile strength of a rope, and a rope’s working load. Both terms refer to rope strength but they’re not the same measurement.

A rope’s tensile strength is the measure of a brand-new rope’s breaking point tested under strict laboratory-controlled conditions. These tests are done by incrementally increasing the load that a rope is expected to carry, until the rope breaks. Rather than adding weight to a line, the test is performed by wrapping the rope around two capstans that slowly turn the rope, adding increasing tension until the rope fails. This test will be repeated on numerous ropes, and an average will be taken. Note that all of these tests will use the ASTM test method D-6268.

The average number will be quoted as the rope’s tensile strength. However, a manufacturer may also test a rope’s minimum tensile strength. This number is often used instead. A rope’s minimum tensile strength is calculated in the same way, but it takes the average strength rating and reduces it by 20%.

A rope’s working load is a different measurement altogether. It’s determined by taking the tensile strength rating and dividing it accordingly, making a figure that’s more in-line with an appropriate maximum load, taking factors such as construction, weave, and rope longevity into the mix as well. A large number of variables will determine the maximum working load of a rope, including the age and condition of the rope too. It’s a complicated equation (as demonstrated above) and if math isn’t your strong point, it’s best left to professionals.

However, if you want to make an educated guess at the recommended working load of a rope, it usually falls between 15% and 25% of the line’s tensile strength rating. It’s a lotlower than you’d think. There are some exceptions, and different construction methods yield different results. For example, a Nylon rope braided with certain fibers may have a stronger working load than a rope twisted out of natural fibers.

For safety purposes, always refer to the information issued by your rope’s manufacturer, and pay close attention to the working load and don’t exceed it. Safety first! Always.

If you’re a regular sailor, climber, or arborist, or just have a keen interest in knot-tying, be warned! Every knot that you tie will reduce your rope’s overall tensile strength. Some knots aren’t particularly damaging, while others can be devastating. A good rule of thumb is to accept the fact that a tied knot will reduce your rope’s tensile strength by around 50%. That’s an extreme figure, sure, but when it comes to hauling critical loads, why take chances?

Knots are unavoidable: they’re useful, practical, and strong. Splices are the same. They both degrade a rope’s strength. They do this because a slight distortion of a rope will cause certain parts of the rope (namely the outer strands) to carry more weight than others (the inner strand). In some cases, the outer strands end up carrying all the weight while the inner strands carry none of it! This isn’t ideal, as you can imagine.

Some knots cause certain fibers to become compressed, and others stretched. When combined together, all of these issues can have a substantial effect on a rope’s ability to carry loads.

Naturally, it’s not always as drastic as strength loss of 50% or more. Some knots aren’t that damaging, some loads aren’t significant enough to cause stress, and some rope materials, such as polypropylene, Dyneema, and other modern fibers, are more resilient than others. Just keep in mind that any knots or splices will reduce your rope’s operations life span. And that’s before we talk about other factors such as the weather or your rope care regime…

Minimum Breaking Strength (MBS) and Working Load Limit (WLL), formerly known as Safe Working Load (SWL), are two important strength ratings when it comes to rigging and safety equipment. They vary based on what type of rigging or safety equipment and are identified by manufacturers.

MBS is precisely what it says, the minimum amount of weight you can put on the equipment that would result in equipment failure. This manufacturer’s recommendation is its maximum weight load for lifting equipment.

Due to legal implications the US, and shortly after Europe, began using “working load limit” rather than SWL “safe working load”. However, they mean the same thing.  WLL or SWL is “the breaking load of a component divided by an appropriate factor of safety giving a safe load that could be lifted or carried.”

Both of these load numerical limits are assigned to lifting and/or rigging equipment. Overhead lifting equipment include hooks, shackles, straps, rope, line and equipment like cranes or other lifting devices. Manufacturers assigned a working load limit on these products.

The incorporation of various materials changes your working load limits. The strength of these materials is known as the mechanics of materials and deals with the behavior of solid objects and how they handle stress and strain.

The strength of a material is its ability to withstand an applied load without failure. A load applied to a mechanical member will induce internal forces within the member called stresses when those forces are expressed on a unit basis. The stresses acting on the material cause deformation of the material in various manner. Deformation of the material is called strain when those deformations too are placed on a unit basis. Therein lies the importance of knowing what materials are working with and what your load limits are for all equipment involved in your rigging and hauling.

There is a wide array of rigging accessories needed in hoisting and rigging. Henssgen Hardware is an industrial rigging hardware supplier. The rigging hardware we carry include: snap hooks, pulleys (fixed eye and swivel with single and double sheave), quick links, shackles, wire rope clips, drop forged clevis grab and clevis slip hooks.

Our rigging hardware is manufactured in stainless steel, solid brass, die cast zinc alloy, zinc plated malleable iron and zinc plated. All of our snap hooks are equipped with stainless steel springs. When dealing with expensive equipment, important loads and your safety, you must have quality hardware. Henssgen is committed to providing each one of our customers with the best.

The definition for safe working load is the breaking load of a component divided by an appropriate factor of safety giving a safe load that could be lifted or be carried.

The working load limit is that it is the maximum mass or force which a product is authorized to support in general service when the pull is applied in-line, unless noted otherwise, with respect to the centerline of the product.

Working load limits are calculated on straight line pulls only. Never side load. Other conditions such as extreme temperatures, chemicals solutions or spills, vapors, or immersion in salt water can reduce the Working Load Limit. Welds to any steel products can also void out a Working Load Limit rating.

It can be confusing to decrypt all of these acronyms like SWL, NWL, WLL and MBS. But Henssgen Hardware is here for you, to educate you on terms like Working Load Limits and everything you need to know about our products.

Safe Working Load, SWL, (or Normal Working Load, NWL) is an outdated term that was used to indicate the amount of weight that a lifting device could safely carry without fear of breaking. It is a calculation of the Minimum Breaking Strength, or MBS.

The specific definition for the Working Load Limit (WLL) is: The maximum mass or force which a product is authorized to support in general service when the pull is applied in-line, unless noted otherwise, with respect to the centerline of the product.

The manufacturer designates the right or approximate WLL value for each lifting device or use, and considers many factors including the applied load, the length of each rope or line, and many other factors.

It is critically important to heed this number, which is set forth by the manufacturer, when lifting with any device, including a line, rope or crane. The number is calculated by dividing the Minimum Breaking Strength (MBS) by a safety factor that is assigned to that type and use of equipment, generally ranging from four to six unless a failure of the equipment could pose a risk to life. In the event that the failure of the equipment could pose a risk to life, the safety factor is ten.

For example, if a hook has a Minimum Breaking Strength (MBS) of 1,000 pounds and a safety factor of five, then the Working Load Limit (WLL) would be 200 pounds.

There were legal implications to the term Safe Working Load, so USA standards phased this term out more than twenty years ago, followed by European and ISO standards just a few years afterward. This change took place because of the legal significance placed on the word ‘safe’.

The Americans and Europeans then developed a more appropriate term and definition for the maximum load capacity of a particular lifting device, agreeing to use the term Working Load Limit (WLL) for equipment such as hooks, slings and shackles.

In the cases of cranes, hoists and winches, the term Safe Working Load (SWL) was replaced by Manufacturer’s Rated Capacity (MRC), which is the maximum gross load which may be applied to the crane or hoist or lifting attachment while in a particular working configuration and under a particular condition of used.

Rigging and safety gear purchased from Westech Rigging Supply should be used in strict accordance with all industry and OSHA standards. At no time should rigging or safety gear be used beyond its certified load ratings (aka Working Load Limits). Normal wear and tear should be expected with use of rigging and safety gear; therefore, all gear should be thoroughly inspected before each and every use. Worn or unsafe rigging and safety gear should never be used.

Have you wondered why rigging experts always suggest a sling that has a significantly higher breaking strength than the actual weight of the load you are lifting? The manufacturers know that the rigging used in overhead applications need to have room for error. This is known as the Safety Factor.

Northern Strands manufactures wire rope slings rated up to 36,000 lbs and sells round synthetic slings that are rated up to 140,000 lb capacity. This capacity is the Working Load Limit of the sling, which is the maximum amount of weight or force that the sling"s user is allowed to put on the sling. Note: These slings do not break at the working load limit. These slings are designed with a safety factor of 5:1. This means that 5 times as much force as the working load limit has to be applied to the sling before it potentially fails. This means the wire rope slings have a Breaking Strength of up to 180,000 lbs and the round synthetic slings can withhold up to 700,000 lbs.

Wear - Working load limits are based on slings in brand new condition and a safety factor can help account for normal wear and tear until it is deemed unfit for further use.

Uneven loading - Slings are made up of either wires or fibers that must all share the weight of the load evenly. If any situation arises where the sling is bent or wrapped around an object, there is potential that some of the wires or fibers will be taking on a greater share of the load than others.

Visit Northern Strands website to use the sling tension calculator. The Northern Strands Sling Calculator has been designed to assist you in selecting slings with enough load carrying capacity for your lifting applications. It is your responsibility to assure that the slings you use are appropriate for your application. http://www.northernstrands.com/sling-calculator.aspx

There is almost an endless number of wire rope applications that all have different strength and flexibility requirements.  In order to determine your unique wire rope requirements, it is important to understand the basic configurations and characteristics of wire rope cable that determine its overall strength.  Three primary areas that determine the strength of wire rope cable include:

As shown below, there are 3 basic parts to wire rope: the wire, the strand and the core all combine to form the wire rope.  There is a standard naming convention of wire rope, which is the main component that will determine the strength of wire rope:

There is an inverse relationship between the strength of the wire rope and the flexibility / stretch of the rope as more strands and more wires per strand are added.  As shown below, 1 X 19 is the least flexible but has a high breaking strength.  7 X 7 is more flexible and has medium strength and 7 X 19 is the most flexible but has the lowest breaking strength.

There are numerous configurations of miniature wire cables that we can supply based on your unique requirements.  Below are some of the most common wire strand configurations:

The diameter of each individual wire, in conjunction with the wire configuration will determine the overall wire rope cable diameter.  As the diameter increases, the breaking strength of the wire will also increase.  It is recommended to select a cable with a minimum breaking strength of 10 times the actual load requirement that you need for your project.

There is a large assortment of materials that are used to make wire rope that will all determine the overall strength of the wire.  Some of the materials we offer include Stainless Steel, Galvanized Steel, Tungsten, Nitinol, Vitallium, Inconel, Titanium, and Molybdenum.  Each material not only has different purposes and applications but will also determine the overall strength of the rope.

Additionally, wire rope can be either coated or uncoated.  We have a variety of coatings that also provide different flexibility and strength.  We offer nylon, vinyl, FEP, polypropylene and polyethylene extruded coatings.

There are many considerations that go into determining the overall strength of wire rope and your project has a unique set of requirements.  We look forward to working with you to determine exactly what type of wire rope fits your needs.