Understanding the Difference Between Rated Capacity & Design Factor in Rigging Gear

When it comes to lifting and rigging operations, precision and safety are non-negotiable. Every component—from wire rope slings to shackles—must perform exactly as intended under specific loads. Two key terms that define this performance are Rated Capacity and Design Factor. While often used interchangeably, these terms refer to very different aspects of rigging gear performance.

In this blog, we’ll break down what each term means, how they’re calculated, and why understanding the difference is essential for safe lifting operations. We’ll also explore how these concepts apply under Canadian Standards (CSA, OHS, and provincial safety codes), and why Hercules Crane & Lifting Supplies is your trusted partner for rigging gear, inspections, and compliance support.

What Is Rated Capacity?

The Rated Capacity (also referred to as Working Load Limit, or WLL) is the maximum load that a piece of lifting equipment or rigging gear is designed to safely handle under normal operating conditions.

Rated capacity is determined by the manufacturer through engineering calculations and destructive testing. It takes into account:

• The material strength

• The manufacturing process

• The intended use and configuration

• Environmental conditions (temperature, corrosion, wear)

For example, if a wire rope sling has a rated capacity of 5 tonnes in a vertical hitch, it means it can safely support a load of 5 tonnes when used in that configuration.

What Is Design Factor?

The Design Factor (sometimes called the Safety Factor) is a ratio that provides a margin of safety between the gear’s breaking strength and its rated capacity. It accounts for the unpredictable conditions of real-world use—shock loading, dynamic movement, or wear over time.

For example, if a sling has a Design Factor of 5:1, it means the sling’s breaking strength is five times its rated capacity.

This margin ensures that even if conditions aren’t perfect, the equipment can handle the load safely without failure.

Typical design factors include:

• Wire Rope Slings: 5:1 (per CSA G4)

• Synthetic Web Slings: 5:1 (per ASME B30.9 and CSA standards)

• Chain Slings: 4:1 (per ASME B30.9 / ASTM / ISO)

• Shackles and Hooks: 5:1 to 6:1 (depending on manufacturer and standard)

• Hoists and Cranes: 3.5:1 to 5:1 (depending on load type and service classification)

Canadian Regulations and Standards

In Canada, rigging gear is governed by multiple standards, including:

• CSA G4 – Steel Wire Rope for General Purpose and Lifting Applications

• ASME B30.9 – Slings

• ASME B30.26 – Rigging Hardware

• CSA Z150 – Safety Code on Mobile Cranes

• Provincial OHS Regulations (e.g., Alberta OHS Code, Ontario Regulation 851, Nova Scotia Workplace Health and Safety Regulations)

These regulations ensure that rated capacities and design factors meet strict safety criteria. For example, under Canadian OHS regulations, employers must ensure that:

• Equipment is used within its rated capacity

• Components are inspected regularly and removed from service if damaged

• Only qualified riggers and competent persons calculate and verify load limits

Why the Difference Matters

Misunderstanding rated capacity and design factor can lead to overloading, equipment failure, and serious safety incidents.

Example Scenario:

A rigger sees that a 10 mm wire rope sling has a breaking strength of 50 kN (about 5 tonnes). If they mistakenly assume that’s the safe working limit, they could overload the sling.
However, with a Design Factor of 5:1, the rated capacity would actually be 10 kN (1 tonne). Using the full breaking strength would result in catastrophic failure.

Understanding this difference ensures your lifts are performed safely and within engineered limits.

Inspection and Maintenance Impact

Even when used correctly, rigging gear degrades over time. Wear, corrosion, and fatigue reduce the actual breaking strength, which means the effective design factor decreases.

That’s why regular inspection and testing are essential to maintain compliance with Canadian OHS requirements. Hercules Crane & Lifting Supplies provides:

• Visual and NDT inspection services

• Load and proof testing

• Tagging and certification management

• Repair and re-certification programs

These services ensure your rigging inventory maintains its intended rated capacity and remains within safety margins.

Key Takeaways

⚠️ Always check the manufacturer’s tag or certificate before lifting. Never assume breaking strength equals rated capacity, and never alter or repair gear without re-certification.

Partner with Hercules Crane & Lifting Supplies

At Hercules Crane & Lifting Supplies, we understand that rigging safety starts with knowledge. From selecting the right sling to proof-testing your lifting hardware, our experts help you maintain compliance with CSA and OHS standards across Canada.

We offer:

• Certified rigging gear and lifting hardware

• Inspection, testing, and repair services

• Customized rigging solutions for industrial, construction, and marine applications

• On-site and in-house training on safe lifting practices

📞 Contact your local Hercules branch today or visit www.herculescrane.ca to discuss how we can help keep your lifting operations safe, efficient, and compliant.