This is a discussion of the shock hazards associated with electric guitars and amplifiers, created in response to comments and questions received after I posted the Death Capacitor video. In it, I explain the source and nature of the shock hazards and how to avoid and eliminate them. I hope this information is both interesting and informative, and helps to spare you from a painful shock….or worse.

What Is The Difference Between SWL vs WLL?

WLL – Working Load Limit: This is the number marked on a piece of equipment indicating the maximum load that is safe to apply to it. It is a number established by the manufacturer of the item based on its known Minimum Breaking Strength (MBS) to which they will then factor in a margin of safety to get the final number. WLL’s are predominately found on lifting and rigging equipment and not on rope access equipment.

SWL – Safe Working Load: This is a number you will rarely find marked on any equipment. It is a number derived from a formula worked out by a competent person based on the Minimum Breaking Strength of the item. The standard formula is currently 10% of the MBS for items of fabric (tape slings, ropes, etc.) and 20% of the MBS for items of metal. Almost all equipment used by the rope access technician is marked only with the MBS.

It is very important to ensure that you are aware of the markings and numbers on all the equipment you are using and their meanings. Confusing an MBS and a WLL and then using the wrong piece of equipment can have serious consequences

Safe Working Load, SWL, (or Normal Working Load, NWL) is an outdated term that was used to indicate the amount of weight that a lifting device could safely carry without fear of breaking.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 more up-to-date phrase for the term SWL is Working Load Limit, or WLL.

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.

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.

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.